Journal of World Prehistoty, Vol. 10, No. 2, 1996 Human Biology in the Classic Maya Collapse: Evidence from Paleopathology and Paleodiet Lori E. Wright 1,3 and Christine D. White 2 We review evidence from human biology--paleopathological and isotopic paleodietary studies on ancient Maya skeletons--to assess the validity of ecological models of the Classic Maya collapse, in which elevated disease and deteriorating diet are commonly assumed. To be upheld, the health arguments of ecological models require that the Maya disease burden (1) was greater than that for many other societies and (2) increased over the span of occupation. The dietary argument requires (1) consistent change in diet from Preclassic and Early Classic Periods to the Terminal Classic and (2) increasing social divergence in diet. A correlation between diet and disease is necessary to link these arguments. Neither pathology nor isotopic data consistently support these criteria. Instead, it appears that local environmental and political factors created diversity in both disease burden and diet. In view of the human biological data, we are skeptical of ecological models as generalized explanations for the abandonment of Classic Maya sites in the southern lowlands. KEY WORDS: Maya collapse; palcodiet; paleopathology; stable isotopes. INTRODUCTION The rise and demise of complex society in tropical regions have been a recurrent focus of anthropological fascination. To Western scholarship, tropical forest cities have historically been shrouded in mystery behind 1Department of Geology, McMaster University, Hamilton, Ontario L8S 4M1, Canada. 2Department of Anthropology, University of Western Ontario, London, Ontario N6A 5C2, Canada. a'I'o whom correspondence should be addressed. After August 1996: Department of Anthropology, Texas A&M University, College Station, Texas 77843-4352. 147 0892-7537/96/0600-0147509.50/09 1996Henum Publishing Corporation 148 Wright and White fronds of encroaching vegetation. Hence the ancient Maya civilization of Central America is often characterized as curious, in both popular and scholarly works, and viewed as an ecological anomaly of high culture that developed in a tropical backwater despite all odds. This mystique is reinforced by the collapse of many large Maya cities in the southern part of the lowlands, centuries prior to the arrival of the Spanish in the New World. The fate of the Late Classic populace has been a central issue in Maya studies since the first explorations of abandoned temples in the nineteenth century. Although recent work is beginning to emphasize the role of sociopolitical turmoil (Demarest, 1992; 1993; Fash, 1994; Miller, 1993; Suhler and Freidel, 1992), ecological considerations in this demographic transition remain of paramount importance for many scholars (Culbert, 1988; Santley et al., 1986; Webster et al., 1992). Ancient Maya civilization flourished in lowland Guatemala, Mexico, Belize, and Honduras from about 900 BC to AD 900. Settlement studies indicate that population density increased substantially over the Classic Period, AD 50-900 (Ashmore, 1981; Culbert and Rice, 1990). Supported by a complex agricultural system, Classic Maya cities were home to a diverse population of farmers, traders, artisans, and religious specialists. Many sites in the south central Maya area (especially the Guatemalan Pet6n and Belize) were abandoned near the end of the first millenium AD (Culbert, 1973). In the humid southern lowlands only a few communities persisted near the central Pet6n lakes (D. Rice, 1986; P. Rice, 1986; Rice and Rice, 1984), but cities continued to flourish in the dry northern lowlands of Yucatan and in the Maya Highlands of Chiapas and Guatemala during Postclassic and Colonial tim.es. A prevalent group of models invokes increasing population density over the span of the Classic Period and environmental degradation attendant with overpopulation as an ultimate cause of the collapse of Late Classic polities (Culbert, 1988; Santley et al., 1986; Webster et al., 1992; Willey and Shimkin, 1973). The reasoning behind this argument is as follows. In tropical forests, the bulk of nutrients is held in biomass rather than stored in the soils, as they are in temperate regions. Thus, when the forest is cut for swidden or "milpa" agriculture, nutrients are rapidly exhausted and the soils are prone to erosion from heavy tropical rains. Under conditions of population growth, milpa farming becomes extensive and expansive. The expansive cycle of Maya agriculture is argued to have reached a critical point in the Late Classic Period, where production could not keep pace with increasing consumer demands due to the degradation of agricultural fields from overuse and erosion. Under pressure to produce sufficient food, farmers are argued to have responded by cultivating more high-yield crops, especially maize. Together with heavy predation of wild faunal populations, Human Biology in the Classic Maya Collapse 149 agricultural stress would have resulted in a gradual deterioration of both dietary quality and quantity. In turn, nutritional stress compounded other health problems, especially infectious disease. In synergism, malnutrition and infection took their toll on the demographic structure of the population, elevating both childhood and adult mortality and precipitating a demographic collapse (Santley et al., 1986; Santley, 1990). In short, Classic Lowland Maya civilization was defeated by environmental limitations. Biological data gleaned from human skeletons played a significant role in the development and tenacity of such "ecological" explanations for the collapse in Maya scholarship. With recent advances in the decipherment of hieroglyphics, we now have a better understanding of the political history of individual Maya citystates, and the role of the charismatic power and prestige of the ruler in local and interregional interaction (Culbert, 1991; Demarest, 1992; Freidel, 1986). These new data are also contributing to a better understanding of the role of interpolity conflict in the collapse of individual city-states in some regions (Demarest, 1993; Fash, 1994). Ongoing excavations highlight the extremely variable occupation histories of neighboring sites even within regions (Demarest and Houston, 1989, 1990; Demarest et al., 1991, 1992; Vald6s et aL, 1993). This is in marked contrast to earlier models of the collapse that tended toward regional or pan-lowland generalizations and from whence arose the generalized "ecological" scenario sketched out above (Culbert, 1973). Newly armed with this political information, recent scholarship highlights the ninth century AD as one marked episode in a series of periodic florescences and collapses (Fash, 1994; Marcus, 1995; Demarest, 1992). Despite this new intraregional and political focus, considerations of the collapse often retain an environmental element, in support of which human biological data may be cited (e.g., Webster et al., 1992). This tendency is rooted in a common assumption that bioarchaeological studies have documented the deterioration of diet and health over the span of the Classic Period. Summarizing this perception, Sharer (1994, p. 344) states, That the ancient Maya were vulnerable to epidemic disease is indicated by skeletal studies at Tikal, Altar de Sacrificios, and Copan. These studies demonstrate progressive nutritional deficiencies and increasing disease potentials in lowland populations toward the end of the Classic period, owing probably to food shortages, crowding, and overpopulation. In this paper, we review the biological data and recent research on Maya paleodiet and find that this conclusion might be premature. Ecological explanations for the collapse are buttressed by the observation that traditional peoples living in today's tropical forests have low population density and typically use extensive agricultural methods--a natural outcome of limited available analogies. For example, (1) there are 150 Wright and White no surviving indigenous complex civilizations in tropical forest environments to use for comparison. Although a number of complex societies arose in such habitats around the world, most had collapsed prior to the integration of world systems which began in the sixteenth century. Moreover, (2) modem Western culture is derived from early civilizations which developed in temperate environments. Finally, (3) tropical rain forests remain one of the last frontiers of agrotechnological development today. This ecological model took hold during the 1960s, when large-scale settlement studies began to reveal an apparent contradiction between the ubiquity of settlement remains (and the high population density implied by them) and the extensive swidden agricultural system employed by modern Peteneros. As this contradiction became apparent, it set off a flurry of research into subsistence alternatives that might have fed the burgeoning Classic populace (Harrison and Turner, 1978). Evidence came to light that agricultural terraces were constructed to combat soil erosion and wetland areas were drained for intensive horticulture (Siemens and Puleston, 1972; Turner, 1974). These intensive agrosystems would have been much more sustainable than swidden. While this work might have alleviated concerns about environmental limitations on Maya cultural elaboration, agricultural intensification was often taken as evidence for unsuccessful adaptation to environmental pressure (Adams, 1983; Culbert, 1988), and the failure of these intensive systems is cited as a trigger for the collapse (Harrison, 1977; Healy et al., 1983). Although wetland agriculture was not as widespread as once proposed, and some densely populated areas were not serviced by its high productivity (Adams et at, 1990; Dunning and Beach, 1994; Pope and Dahlin, 1989), a variety of soil management strategies was adapted to local conditions that may have permitted sustained cultivation (Dunning and Beach, 1994; Fedick and Ford, 1990). Although the magnitude of population growth over the Classic Period was dramatic, the notion that agricultural systems were stretched beyond capacity is now being questioned (Turner, 1990). It was reasonable to assume that modem Petrn milpa agriculture ought to have been an appropriate analogy for the interpretation of prehistoric agrosystems, but it now appears that our understanding of modem agriculture was inadequate to appreciate the subtleties of indigenous Petrn agroforestry. Research with the Itz~ and the Lacandon Maya suggests that more complex forest management strategies and cropping systems may have been fundamental to prehistoric agronomy (Arran, 1993; Barrera et aL, 1977; Nations and Nigh, 1980). This indigenous agroforestry system mimics the diversity of the rain forest and preserves soil cover, a stark contrast to the essentially Ladino milpa system. It should also be noted that Petrn farming systems were dramatically changed by the Spanish colonial structure, which Human Biology in the Classic Maya Collapse 151 placed heavy demands on local farmers to produce surplus maize, and discouraged the cultivation of foods other than storable grains (Schwartz, 1990, p. 62; Atran, 1993, pp. 640, 676). Instead, prehistoric Maya agriculture was probably based on "fixed plot variable fallow farming," a land-use strategy emphasizing intensive ongoing use of spatially discontinuous permanent fields through various stages of cultivation (McAnany, 1995; Fash, 1994). Although the Classic landscape was clearly a culturally modified environment (Rice, 1993), it did not likely emphasize extensive maize monocrop agriculture as once envisioned. Moreover, the occurrence of faunal remains of forest species such as tapir, jaguar, and monkeys implies the maintenance of some primary forest refugia (Pohl, 1990; Emery, 1991). The argument that environmental degradation lay behind the demographic decline gained strong support from sedimentology and palynological studies of lake cores from Central Pet6n (Deevey et al., 1979; Rice and Rice, 1984). These document substantial erosion over time due to human intervention and forest clearance. The pollen data show the replacement of forest trees with maize, cultigens, and successional species during the peak occupation. A brief increase in maize pollen during the final years of Maya occupation, interpreted as a last-ditch attempt to produce enough food to feed a starving populace, is followed by a dramatic resurgence of forest tree pollen (Wiseman, 1985). In the original analysis, this forest rebound was assumed to correspond to the collapse, but recent paleolimnological work southwest of Lake Pet6n Itz~i indicates that forest regrowth did not occur until the mid seventeenth century (Brenner et al., 1990). Although considerable spatial and chronological variability in reforestation might be expected after the collapse, these data imply a primarily agricultural landscape for the lake region until the Spanish reducciones of the early 1700s (Rice and Rice, 1994; personal commmunication, 1995). These data call into question the precipitous nature of environmental disaster in the Terminal Classic Central Pet6n. Likewise, the extent of depopulation may have been less complete than often assumed. As with many Late Classic residences that are missed by surface survey (Johnston, 1994), many Postclassic and Colonial structures may have been archaeologically invisible (Jones, 1989). As Fash notes (1994, p. 188), fairly large and organized populations may well have persisted long after the collapse. A key element of ecological models is the argument that maize-based diets are unable to meet nutritional requirements. For instance, Saul (1972, 1973) and Santley et al. (1986) argue that Maya diets were deficient in iron, niacin, and the amino acids tryptophan, lysine, and methionine and imply that the entire population was malnourished. However, the nutritional drawbacks of raw maize are alleviated by consuming complementary foods, such as beans, which are high in tryptophan and help to complete 152 Wright and White the protein, and by processing maize with alkali, which significantly improves the balance of amino acids, makes more niacin available, and adds calcium (Bressani et al., 1958; Bressani and Scrimshaw, 1958; Katz et al., 1974). Diets with a substantial component of processed maize with beans are generally sufficient to meet the protein needs for adults but may be inadequate for the higher metabolic demands of children, and cannot supply them with sufficient iron. But behavioral factors also play a role in subadult undernutrition. Children often suffer from appetite loss due to intestinal and respiratory infection, so simply do not eat enough to supply nutrient demands even when adequate food is available (Beh~ir, 1977; Mata and Salas, 1984). It is important to note that the bulk of skeletal evidence for nutritional pathology relates to health status during growth and development, measuring the health of children, not adults. Early speculations on the collapse did include epidemic disease (Spinden, 1928), but the proposition that nutritional disease could have played a role in the collapse was first raised by Hooton (1940) with skeletal data. The nutritional hypothesis gained prominent support because of two osteological reports: Haviland's (1967) study of stature at Tikal, which suggested a decline in health over the span of the Classic Period, and Saul's (1972) detailed monograph on Maya osteology at Altar de Sacrificios. Both works were landmarks in the emerging field of bioarchaeology, demonstrating the richness of data that could be gleaned from human skeletal remains. They provided skeletal indications that health may have been compromised among Classic Maya populations and hypothesized that health burdens may have changed over time. It is important to recall that comparative paleopathological data from other cultures were very limited at this time, so Maya disease burdens could not be evaluated in a wider context. Although Saul (1972) hesitated to attribute depopulation directly to disease and malnutrition, he argued that the lowland Maya teetered on an unhealthy precipice, prone to collapse. Archaeologists have generally not heeded his caution, and assert that the osteological data provide evidence of "starvation" (Ix)we, 1985, p. 92; see also Tainter, 1988, p. 174). Yet few, if any, osteologists would claim an ability to diagnose "starvation" per se from skeletal remains. The malnutrition hypothesis derives its greatest support from the health status of the modern Maya in highland Guatemala (Scrimshaw and Tejada, 1970), who rely on maize for a significant proportion of their daily sustenance. Together with impoverished Ladino populations, the Maya are often used in studies of growth and development, and provide models for poor nutrition and health (Beh~ir, 1977; Bogin, 1988; Bongaarts and Delgado, 1977; Scrimshaw et al., 1968; Sibri~in and E!ston, 1990; Martorell, 1992). However, this direct analogy presupposes that the agricultural base Human Biology in the Classic Maya Collapse 153 of modern Maya peoples is analogous to that in prehistory and that modern diets are constrained by long-standing emic cultural preferences. This is far from the truth. Over the twentieth century, indeed since the sixteenth century, highland Maya peoples have seen their land holdings rapidly diminish at the hand of coffee plantations, to the point where few families have enough farm land to provide their basic staple foods (Perera, 1993; Schwartz, 1990; Stoll, 1993). Hence most concentrate on high-yielding maize and must buy a large proportion of their food. Since the purchase of animal protein is not in their grasp, dietary possibilities are further limited. We should also note that, despite widespread malnutrition, high infant mortality, and political conflict, highland Maya populations have actually grown at an exponential rate during the twentieth century (Early, 1982). They are not on the brink of demographic collapse. Although we have ourselves been guilty of drawing too liberally on this modern analogy, it is important to recall that the highland Maya are not living fossils, but a vibrant people coping with a very different social dynamic than did their ancestors. In this paper, we review recent advances in Maya osteology, with the aim of reevaluating archaeological reconstructions of the diet of the ancient Maya and the role of nutritional factors in the demographic transition of the eighth and ninth centuries AD. A florescence of research on Maya osteology in recent years is the result of larger and more representative skeletal samples than were available to early workers and rapid advances in bioarchaeological methodology over the last few decades. In particular, isotopic techniques provide a new avenue by which to reconstruct food consumption from skeletal remains. In this review, we distinguish a nutritional argument that is typically subsumed within ecological explanations of the collapse and find that the biological evidence for malnutrition as a causative agent of demographic collapse is weaker than generally assumed. Although the case for an environmental catastrophe can be made independent of the nutritional mechanism, we find little support for generalized ecological models in paleodietary data. Instead, the Maya Lowlands show considerable diversity in dietary and health indicators, implying that local environmental and social conditions were key factors defining Classic Maya paleoecology. LOWLAND MAYA HEALTH: EVIDENCE FROM PA1,EOPATHOLOGY Of the abundant pathology documented in osteological studies of Maya skeletal remains, evidence of anemia, infection, and growth disrup- 154 Wright and White tion has been marshaled to demonstrate that the Late Classic Maya society was poorly adapted to its environmental surroundings. In terms of the ecological model, we can ask three critical questions of the paleopathological data from the Maya lowlands. (1) What is the total disease burden on the population? How does it compare to other complex agricultural societies, and to modern populations whose health status is better understood? (2) Is there evidence of a change in health status over the span of Maya occupation? Can we document a gradual deterioration in health that is correlated with increasing population density? (3) Is there a relationship between nutritional pathology and food consumption, as reconstructed isotopically from bone? These questions arise from the contexts in which osteological data have been used in the archaeological literature as evidence to support the argument that health deterioration made a critical contribution to the collapse. For instance, Hammond (1982, p. 140) describes "a decrease in nutritional standards, detected in the skeletons of Late Classic burials, increased susceptibility to endemic diseases, which may have become epidemic." Likewise, Freidel and Schele (1990, p. 489) state that "at Copan... the voiceless remains of the d e a d . . , bear witness to malnutrition, sickness, infection, and a hard life indeed," echoing a common assumption that health "stress levels increased dramatically in Classic times" (Santley, 1990, p. 329). With respect to the question of disease burden we must first emphasize that differing epidemiological circumstances mitigate against direct inference of disease burden from raw frequencies of paleopathological indicators. Because skeletal response to disease is nonspecific and many diseases do not affect bone, we cannot make absolute statements about the quality of life. In general terms, however, we can evaluate a common perception among Mayanists, impressed by Saul's (1972) pathology photos, that disease was anomalously high among the Maya. Due largely to Haviland's (1967) proposition that health declined with increasing population density and agricultural stress at Tikal, ecological models generally invoke a gradual deterioration in the state of health over the span of the Classic Period. Hence, we should expect to see an increase in the prevalence and severity of paleopathological conditions over time. Admittedly, debate currently wages over paradoxical interpretations of the relationship between the prevalence of pathology in mortality samples and the health of the living population from which they are drawn (Cohen, 1994; Goodman, 1993; Jackes, 1993; Wood et aL, 1992). We agree that the interpretation of paleopathology data is complex and not always intuitive. Because skeletal data have been used to support an ecological model on Human Biology in the Classic Maya Collapse I N ~ j AJm tr Fig. L Map of the Maya area showing the locations of sites mentioned in the text. 155 156 Wright and White this basis, for the purpose of this review, we follow the traditional assumption that higher levels of skeletal pathology imply poorer health. With the recent increase in osteological work on the Maya, we are now in a better position to evaluate the severity of paleopathological data. Regardless, sample sizes for pathological indicators remain small. In the tables, we cite the proportion of individuals affected by a condition with respect to the number of skeletons for which that particular bone element is present and scorable as reported by each researcher for each skeletal series. Hence, sample sizes for each site are much smaller than is apparent from the total number of skeletons excavated. Our review here uses the data published to date, but we must emphasize that ongoing work will clarify current patterns and no doubt raise further questions. We include data on Postclassic and Historic health in our review to provide greater time depth to the observed trends. Moreover, the biological consequences of the Spanish conquest, although still inadequately documented, provide a counterpoint to the posited health transition of the Classic collapse. Figure 1 illustrates the locations of sites mentioned in the following discussion. Paleodemography Understanding the Classic Maya collapse is fundamentaly a demographic problem. Osteological paleodemographic data have been brought to bear upon this issue, beginning with Saul's (1972) description of a (statistically nonsignificant) decrease in mean age at death of skeletons from Late Classic Altar de Sacrificios, a key study which led some to speculate that elevated mortality had a major impact on the collapse (Willey and Shimkin, 1973; Santley et al., 1986). Subsequently, Sattenspiel and Harpending (1983) cogently argued that the mean age at death in cemetery samples bears little relation to mortality. This and other problems inherent in paleodemographic reconstruction (Bocquet-Appel and Masset, 1982, 1985; Buikstra and Konigsberg, 1985; Van Gerven and Armelagos, 1983; Wood et al., 1992) are of particular concern in the Maya Lowlands, where recovery of infant remains is especially compromised. At present, Copfin is the only Classic Maya site where archaeological sampling has been adequate to permit a serious attempt at osteological paleodemography. But even at Cop~m, undersampling of burials from the earlier phases of occupation limits the reliability of demographic reconstructions of the growth of the Classic Period population (Fash and Sharer, 1991). Using survival analysis, Whittington (1991) suggested that decreased fertility may have contributed to the decline in the low-status population of Cop~in. On reanalysis of the same skeletal series using likelihood analysis Human Biology in the Classic Maya Collapse 157 to fit model life tables, Paine (1992) concluded that is was not possible to obtain reliable estimates of fertility, mortality, or migration from the skeletal data alone. However, his event history analyses of settlement abandonment does indicate that residences on prime agricultural land were maintained longest, providing support for the argument that agricultural degradation contributed to the population loss. Rather than relying on paleodemography to reconstruct patterns of fertility and mortality, it is more fruitful at this time to focus on factors that directly affect fecundity and survivorship, i.e., health and nutritional status. Nutritional Disease Anemia Skeletal manifestations of anemia have played an important role in the development of the nutritional argument of the ecological model of collapse. In extreme anemia, the hemopoietic tissues expand to counterbalance the blood deficit (Weatherall and Wasi, 1990). In young children, the expansion of diplre in the orbits and cranial vault can perforate the thin external table of bone, producing a distinctive skeletal lesion known as porotic hyperostosis. In young children, the initial reaction is pitting and perforation of the orbital roof (called cribra orbitalia) (Stuart-Macadam, 1989). In older children, continued anemic stress produces pitting of the external table of the cranial vault and the deposition of new perpendicular bone that is responsible for the characteristic "hair-on-end" radiographic image (Aksoy et al., 1966; Burko et al., 1961). Because hemopoietic marrow is gradually replaced by fatty marrow with age, anemia cannot initiate porotic hyperostosis in adults, although remodeled lesions of childhood anemia may persist in the adult cranium (Stuart-Macadam, 1985, 1987). Evidence of anemia, therefore, speaks only to health status during growth and development, not during later life or, for adults, at the time of death. Because there is no good evidence of genetic hemolytic anemia as in the Old World, high frequencies of porotic lesions in New World archaeological skeletons are typically attributed to iron deficiency anemia and often linked to dependency on maize agriculture (Saul, 1977; E1-Najjar, 1977; E1-Najjar et aL, 1976). In many areas, porotic hyperostosis increases with the transition to agriculture, supporting the interpretation of the lesion as an indicator of nutritional stress (Cohen and Armelagos, 1984, p. 587). However, porotic hyperostosis is also prevalent in skeletal series from a variety of environmental contexts, indicating that parasitic infection causing 158 Wright and White blood loss also contributes to the etiology of the lesions (Palkovich, 1987; Ubelaker, 1992; Walker, 1986). Hooton (1940) observed porotic hyperostosis on crania from the cenote at Chichen Itza. The etiology of these porotic lesions was not firmly identified at that time. Hooton speculated that they might be scorbutic and ventured that they "may have been caused by dependence upon a diet consisting mainly of maize" (Hooton, 1940, p. 276). He noted that the pathology was abundant and dramatic but not unprecedented, as comparable examples could be found in skeletal collections from Peru. Nonetheless, Hooton (1940, p. 276) offered the suggestion that nutritional disease may have "caused the downfall of the Maya civilization." At the time of his writing, chronological alignments of Mesoamerican civilizations were uncertain, and the cenote deposits not securely dated. In retrospect, the health of the Postclassic Cenote skeletons cannot directly address the collapse of the Classic Lowland Maya, but it did contribute to a perception that the Maya were anomalously ill. This nutritional suggestion was later supported by Saul's (1972) observation of frequent anemic lesions during the Classic Period at Altar de Sacrificios and became the basis for the nutrition argument of the emerging ecological model of collapse (Willey and Shimkin, 1973). By this time, a nutritional cause for New World porotic hyperostosis was widely accepted (Moseley, 1965). Saul documented abundant healed lesions on adult crania from Altar de Sacrificios and argued that the frequency of anemia was particularly extreme and contributed to a debilitating health burden that would have significant impact on population survival. Ideally, it would be best to examine active lesions of porotic hyperostosis in the skeletal remains of children, but subadult sampling is notoriously poor in the Maya area, due to preservation bias against immature remains and the combined biases of the dispersed locations of Maya burials and archaeological sampling strategies. Hence, intersite comparisons of anemic lesions must emphasize lesions on adult crania. The diagnosis of porotic hyperostosis in adults is complicated by the extent of sclerotic remodeling, which can mimic other scalp infections. Most researchers require both porotic lesions and increased vault thickness to identify lesions in adults, but scoring may not be entirely consistent between researchers. Cohen et al. (1994) suggest that interobserver error may partly account for the variability reported. For instance, Saul (1972) recorded higher prevalences of lesions at Altar than did Wright (1994) on restudy. However, substantial differences in porotic hyperostosis occur between sites studied by a single observer (Whittington, 1989; Whittington and Reed, 1996) and chronologically at a single site (White, 1986; White et al., 1994). Hence, small differences between studies are not terribly meaningful. Human Biology in the Classic Maya Collapse 159 Table I. Frequency of Porotic Hyperostosis in Mayan and Comparative Skeletal Series Adults Subadults Skeletal series Reference % N % N 12.5 58.8 55.5 77.8 * * * 35.8 * 8 17 18 18 3.6 60.0 65.4 52.9 48.0 9.0 17.0 19.4 3.0 28 30 81 17 28? 53 100 185 36 Saul & Saul, 1991 Whittington, 1989 Wright, 1994 Hooton, 1940 Marquez Morfin, 1982 White, 1986 White, 1986 Cohen et al., 1994 Whittington & Reed, 1994 ---33.3 14.9 45.9 65.0 19.9 67.8 ---393 67 61 20 156 277 Lallo et al., 1977 Maya series Cuello Preclassic Copfin Classic Pasi6n (combined) Chichen Itz,'t cenote Playa del Carmen~ Lamanai Postclassic Lamanai Historic Tipu Historic Iximch6 Comparative series Dickson Mounds Libben Arroyo Hondo California Coastal Chiribaya AIta, Peru Canyon de Chelly Pueblo Chaco Canyon Nubiab Medieval York, UK i i 34.6 44.4 25.9 51.3 53.3 88.0 83.8 23.2 43.2 106 101 241 54 37 91 17 12 129 183 Mensforth et aL, 1978 Palkovitch, 1987 Walker, 1986 Burgess, 1996 E! Najjar et aL, 1976 El Najjar et aL, 1976 Carleson et aL, 1974 Grauer, 1993 i "Subadult data are included with adult statistics for these samples. bData refer to cribra orbitalia instead of porotic hyperostosis of the cranial vault. The prevalence of porotic hyperostosis is quite high in Maya series, reaching 77% in subadults and 65% in adults (Table I). In general, the subadult prevalences are not out of place with statistics for other maize growing cultures, such as Woodland and Mississippian North Americans (Lallo et al., 1977; Mensforth et al., 1978) and Late Intermediate Peruvians (Burgess, 1996). The data are also comparable to Coastal Californians, where the incidence of porotic hyperostosis is linked to parasitism instead of dietary insufficiency (Walker, 1986). However, they are lower than in Southwestern Pueblo maize agriculturalists at Canyon de Chelley and Chaco Canyon (E1-Najjar et aI., 1976), where the prevalence of porotic hyperostosis may be more firmly linked to maize agriculture, though differences in parasitism also contribute to the southwestern trends (Reinhard, 1988). Among adults, the Maya series show more abundant lesions than some North American groups but are comparable to the Southwestern Pueblo adults. The Maya data are also remarkably similar to the prevalence of porotic hyperostosis recorded for Medieval York, where malnutrition and infection produced a high level of pathology (Grauer, 1993). Thus, on the grounds of lesion prevalence alone, we can- 160 Wright and White not confirm the perception that the ancient Maya were affected by anemia to an anomalous extent. Substantial geographic variability in porotic hyperostosis expression is evident among Maya sites. Although scoring differences are undoubtedly a factor, this regional variation may also be related to differences in both dietary and parasitic stress loads. Lesions of porotic hyperostosis are unusually abundant among the Chichen Itza cenote skeletons (Hooton, 1940), and we suspect that children deposited here were not randomly selected from the local populace. In contrast, it is possible that pathological juvenile crania are underrepresented at other sites due to their differential decay. Among adults, the cenote crania show levels of porotic hyperostosis comparable to those of Cop~in and the Pasi6n sites Altar de Sacrificios, Seibal, Dos Pilas and Aguateca (Whittington, 1989; Wright, 1994). Lower prevalences are recorded for Tipu, Lamanai, Cuello, and Iximch6 (Cohen et al., 1994; Saul and Saul, 1991; White, 1986; Whittington and Reed, 1996). If the occurrence of porotic hyperostosis is linked to maize dependency among the Maya, lower or lighter carbon isotopic values for Classic Period Lamanai and Preclassic Cuello might explain part of this trend. Anemic scars are more abundant at Postclassic Lamanai than during the Classic Period, a change that does seem to be correlated with increased maize consumption (White, 1986). In contrast, at Iximchr, maize consumption as measured isotopically was high, and yet it has the lowest frequency of porotic hyperostosis (Whittington and Reed, 1993). Based on a small sample of skeletons from Tancah with few anemic lesions, Saul (1977, 1982) suggested that fish consumption at coastal sites might offset dietary iron deficiency suffered at inland sites. Ironically, fish are also a source of parasites which could contribute to iron deficiency anemia (e.g. Walker, 1986). Porotic hyperostosis is certainly abundant at some coastal sites, such as Playa del Carmen, where M~rquez Morffn et al. (1982) report the lesions in 48% of skeletons (not separated by age). Moreover, fish do not contain especially high iron levels (INCAP,, 1961). We suspect that variability in parasitic infection may account for much of the variability observed in porotic hyperostosis among the Maya. Scrimshaw and Tejada (1970, p. 208) observe that hookworm infection accounts for a substantial proportion of anemic cases in Guatemala City hospital admissions. Although it was once thought that the hookworm Ancylostoma duodena& was introduced to the New World in historic times, coprolite evidence now supports an indigenous origin (Reinhard, 1990; Home, 1985). Climatic variability across the Maya area likely controls the distribution of the nematode and its impact on human health, as the larvae can survive only at temperatures between 70 and 85"F (Beck and Barrett-Connor, 1971, p. 103). Hence, the parasite may be more abundant in the warm lowlands Human Biology in the Classic Maya Collapse 161 than in the highlands, accounting for the rarity of anemia at Iximch6 and its abundance at lowland sites. Shattuck (1938) illustrates this elevation effect by recording a substantially higher occurrence of hookworm at lowland Quirigua than at highland Guatemala City. Climatic effects will be less significant for other parasitic infections contributing to parasitic blood loss, such as Trichuris, Ascaris, and Strongyloides. It is also interesting to note that in the lowland Pet6n nearly twice the proportion of deaths was attributed to intestinal parasitism each year between 1986 and 1990 than in the highland Guatemalan departments of Quich6, Solol~, and Huehuetenango (INE, 1993). If the incidence of porotic hyperostosis were tightly linked to dietary iron deficiency as argued by proponents of nutritional collapse mechanisms, and nutritional decline contributed to the collapse, we should expect to see a change in the abundance of lesions over time. In the face of declining productivity, if farmers concentrate on high-yielding maize to the exclusion of other crops, following the traditional model, we anticipate increased iron deficiency anemia over time. Alternately, if maize becomes more scarce due to environmental degradation and wild foods are substituted for the deficit of cultigens, one might even expect iron deficiency to improve. Finally, if general food quantity is a problem but there is little change in diet composition, we should see increased iron deficiency. At Altar de Sacrificios, Saul (1972) did not document a chronological change in anemia due to sampling limitations. The sample from Cop~in analyzed by Whittington (1989) precludes the observation of chronological trends due to undersampling of early burials. Ongoing work by Rebecca Storey may soon provide better chronological depth, but these data are not yet available. More recent reanalysis of the Pasi6n valley skeletal series from Altar, Seibal, and the Petexbat6n sites (Dos Pilas and Aguateca) confirms no statistical change in the frequency of healed lesions in adults over time, whether sites are taken independently or the region is considered as a whole (Wright, 1994). At Lamanai, the frequency of porotic hyperostosis rises only slightly from the Classic to Postclassic Periods when isotopic paleodiets show a dramatic increase in maize consumption, but increases much further with the introduction of foreign infectious and parasitic diseases after the Spanish Conquest, a transition not accompanied by dietary change (White et aL, 1994). In summary, the data on ancient Maya anemia do not provide unequivocal support for a nutritional collapse argument. The lesions are not present at anomalous levels when viewed in a global perspective, and changes over time are not generally documented. The considerable variability in porotic hyperostosis expression is more easily accounted for by variability in parasitism with climate and human population density. Ane- 162 Wright and White mia undoubtedly took its toll on the health of ancient Maya peoples, but we find little evidence to identify it as a causal element of the collapse. Whittington (1989, p. 306) has argued that anemia did have a critical impact on the decline of Cop~in on the grounds that porotic hyperostosis lesions are negatively correlated with adult survivorship. Among adults, however, this pattern is anticipated because complete remodeling of lesions will lower lesion abundance in older adults. No such age trends were documented in anemic lesions in the Pasi6n series (Wright, 1994). At this time we are unable to resolve the etiological paradox of whether the abundance of anemic lesions in Maya skeletons is caused by high frailty and susceptibility to a heavy health burden or by high survivorship through protracted childhood anemia that in turn conferred protection against infectious disease (Stuart-Macadam, 1992). Scurvy The second nutritional disease that has received substantial attention with respect to the Maya is scurvy. Vitamin C is necessary for the hydroxylation of proline in the construction of collagen from its constituent peptides and in the maintenance of the vascular endothelial membrane attachments (Ortner and Putschar, 1981). A deficiency in childhood leads to abnormal bone growth with incompletely ossified metaphyses and thin cortices, which are very susceptible to fracture. Extensive subperiosteal hemorrhaging is a key result, due to the weakened vascular tissue. In adults, few skeletal changes occur, other than pathological fractures through rib metaphyses. Periodontal degeneration may occur, which might lead to antemortem tooth loss (Ortner and Putschar, 1981). Saul has proposed that subperiosteal new bone, deposited on the shafts of long bones, indicates that scurvy was common in adults from Altar de Sacrificios (1972), CueUo (Saul and Saul, 1991), and Tancah (Saul, 1982). The diagnosis is problematic in that subperiosteal hemorrhaging is unlikely to calcify under scorbutic conditions due to the inhibition of collagen synthesis. If the patient recovers, some calcification might occur, but this is typically only at the margins of the hemorrhage and is unlikely to be preserved in archaeological materials. To date, very few osteologists have diagnosed scurvy in archaeological skeletons, and their diagnoses have not been generally accepted. As Ortner and Putschar (1981, p. 273) note, the Altar lesions are best interpreted as nonspecific indications of infectious disease (periostitis), while the periodontal resorption cited by Saul is more consistent with a diagnosis of antemortem tooth loss secondary to caries and abscess. In the Maya area, only Kennedy (1983) has followed Saul's H u m a n Biology in the Classic Maya Collapse 163 diagnosis of scurvy. Other osteologists have not diagnosed scurvy in their collections (Cohen et al., 1994; White, 1986; Whittington, 1989; Wright, 1994). Saul supported his diagnosis with the observation that the Yucatec Maya consumed little fruit in the 1920s. Fruit is somewhat less plentiful in the dry Yucatan than in the wet lowlands of the Pet6n. Moreover, it is difficult to estimate fruit consumption in dietary surveys because fruit is often eaten as a snack food, between meals. Declining fruit consumption in the twentieth century is likely due to the introduction of processed sugar (Scrimshaw and Tejada, 1970, p. 208; Danforth, 1989, pp. 20-21). Paleobotanical studies have documented ancient Maya consumption of a variety of fruits, including zapote, nance, ciruela, hackberry, wild grape, and avocado. The Itzfi Maya preserve these species among others and there is little reason to suppose that this practice is not of great antiquity (Atran, 1993). Greens and chile peppers also contain substantial quantities of vitamin C. These are consumed today and have been recovered from archaeological flotation samples (Lentz, 1991; Miksicek, 1983). It is unlikely that the ancient Maya were scorbutic. Growth Disruption Stature Reconstructions of skeletal stature have also played an important role in bolstering the ecological model of collapse. Stature is widely recognized as a general measure of childhood nutrition and health experience and is often used to investigate health differentials in modern and archaeological populations where genetic factors can be controlled. Haviland (1967) observed a decline in both adult male and female stature over the Classic Period at Tikal and increasing stature divergence between tomb and nonelite skeletons. Shortly thereafter, Saul (1972) described a comparable decline in male stature at Altar de Sacrificios. Danforth (1994) has cogently reviewed the data and issues of stature change in Lowland Maya skeletons, and we refer readers to her work. In brief, she notes that the statural data are especially scant due to the limited sample sizes of adequately preserved remains, so that trends can rarely be statistically verified. Methodological issues also complicate the utility of this limited database, especially the large bias introduced by the choice of bone used, and circularity inherent in using dimensional differences as sex-specific health indices when those same measures form the basis of skeletal sex classification. As Danforth observes, the trends described for Tikal and 164 Wright and White Altar have been generalized in subsequent scholarship to a pan-Maya phenomenon, which cannot be confirmed by the limited data available from other sites. For instance, Santley et al. (1986, p. 142) claim a stature reduction at Barton Ramie that was not identified in the osteological report (WiUey et al., 1965). We must also emphasize that the apparent trends at Altar and Tikal are somewhat suspect. At Altar, the decline in male stature is predicated upon a sample of only 11 skeletons spread over the 1500-year occupation span. At Tikal, the trend is more convincing, but is based on a combination of bone measurements, in situ burial measures, and postexcavation reconstructions from burial plans. Given the highty variable nature of skeletal slumping with soft tissue decay, even in the absence of other disturbance, we should be skeptical of the accuracy of these data. Statural data do not provide unequivocal evidence for a change in health status during Maya prehistory. Yet the scant data do support the suggestion, originated by Stewart (1949; 1953), that the modern Maya are of the order of 5 cm shorter than their prehistoric ancestors, a trend paralleled in other Mesoamerican peoples (Faulhauber, 1970; Genovds, 1970; Nickens, 1976; Steggerda, 1941; Williams, 1931). Given that the early colonial Maya from Tipu exceed modern statures but are comparable to archaeological data, it seems likely that most of this reduction came about during Historic times (Cohen et al., 1994; Danforth, 1994) and may be related to nutritional shifts at the hand of Colonial land-tenure transformations as well as increased infectious disease loads. This discrepancy between ancient and modern populations highlights the questionable utility of analogy with modem health conditions in Maya descendants. Dental Development Poor childhood health among the Maya has also been identified through defects in the developing teeth. Enamel hypoplasias--circumferential bands of depressed, thin enamel--form during the development of the tooth crown under conditions of metabolic stress. Hypoplasias appear to be caused by disruption of the secretory phase of enamel formation, which may occur in a variety of disease syndromes or due to the interaction of nutrition and disease. Health disturbances that affect only mineral metabolism produce related defects, known as hypocalcifications, which are irregularly mineralized bands of enamel, that may or may not be associated with any surface contour hypoplastic lesions (Commission on Oral Health, 1982; Goodman and Rose, 1990). At a microscopic level, brief acute stress episodes produce narrow bands of defective enamel known as Wilson bands Human Biology in the Classic Maya Collapse 165 (Rose et at, 1978). Since enamel defects occur at a greater frequency in the dentitions of subadult skeletons than in those of adults (Cook, 1981; Goodman and Armelagos, 1988), they are sensitive indicators of childhood health conditions that contributed to mortality in prehistory. Because teeth are the best-preserved skeletal element, and on occasion the only material recovered from burials in the Maya area, studies of enamel hypoplasia among the Maya have been quite productive. However, the results of different studies are difficult to compare because of different reporting standards and interobserver variability in lesion definition. Hypoplasias have been reported by presence/absence, mean number of defects per tooth, percentage individuals affected, and mean number of defects per millimeter, or 6-month unit of enamel. Unfortunately, these measures are not readily converted to a scale on which defect incidence can be compared between studies. Within the dentition, teeth vary dramatically in the abundance of developmental defects, due to differences in crown architecture, the chronology of tooth development and stress occurrence, and intertooth susceptibility to ameloblastic disruption (Goodman and Armelagos, 1985a; b). Accordingly it is crucial that hypoplasia investigations treat tooth positions consistently and control for missing teeth. Finally, although intraobserver error does not appear to be too severe, investigators may differ substantially in the identification of the less severe hypoplastic events (Danforth et al., 1993). Hence, it is not feasible to draw broad health comparisons between sites with hypoplasia data at this time. Saul (1972) documented abundant hypoplasia on teeth at Altar de Sacrificios and equated the lesions with weanling stresses, thereby painting a picture of poor childhood health. Several investigators have reported that hypoplasias are observed in the dentitions of almost all adult skeletons, indicating a high prevalence of childhood stress episodes, through which the individuals survived (Kennedy, 1983; Saul, 1972, 1973, 1975, 1982, Whittington, 1989, 1992; Wright, 1994). Moreover, Storey (1992a, b) has documented abundant hypocalcifications in deciduous teeth of elite children at Cop~in, indicating inadequate maternal buffering of stress to children in utero. But as Whittington (1992, p. 194) notes, the abundance of lesions is not out of line with that documented for other skeletal series, including Barbados slaves (Corruccini et al., 1985), the Bronze Age Levant (Smith et aL, 1984), the precontact Georgia coast (Hutchinson and Larsen, 1988), Dickson Mounds (Goodman and Armelagos, 1985b), and the HammanTodd collection (EI-Najjar et aL, 1978). Although direct comparison of data collected by different investigators is hindered by differences in reporting and interobserver error, there is little evidence to suggest that childhood health varied dramatically across the 166 Wright and White Maya lowlands. Danforth (1989, 1996) reports no significant differences in the abundance of enamel hypoplasias or Wilson bands in deciduous and adult teeth between Late Classic skeletal series from Tikal, Seibal, and Barton Ramie, despite the discrepancy in social status that might be anticipated among these series. Chronological trends in hypoplasia incidence have been examined at Cop~in (Whittington, 1989, 1992), Lamanai (White, 1986), and Altar de Sacrificios (Saul, 1972) and in the combined Pasi6n series (Wright, 1994). None of these studies reports any statistically significant differences between phases in the total level of stress experienced. Although Classic Maya children suffered a severe health burden, there is no indication that health deteriorated over time or with increasing population density and postulated demographic pressure. It is interesting to note that Danforth (1989) reports a substantially higher prevalence of hypoplasias and Wilson bands in the Late Classic Pet~n series than at Colonial Tipu, indicating that childhood health was indeed worse during the Late Classic Period. This finding seems to contradict the statural data, which indicate continuity between Classic and Colonial Petdn populations. However, both anemia and infection seem to be anomalously rare at Tipu (Cohen et al., 1994), raising the possibility that this settlement had the luxury of more sanitary living conditions, perhaps a consequence of the lower population density. The situation is reversed at Lamanai, where Wilson band frequencies imply an increase in acute morbidity during the early Colonial era over the Postclassic condition. Given the coeval increase in porotic hyperostosis at Lamanai, it is reasonable to attribute this change to Spanish-introduced infectious and parasitic diseases (White et al., 1994; Wright, 1990). Unfortunately, no local Postclassic skeletons are available from Tipu to examine this transition directly. Infectious Disease Infectious disease has been an important element in the ecological model of collapse. Instead of epidemic disease, such as the yellow fever epidemics once proposed by Spinden (1928), infectious disease is generally incorporated into collapse models as a factor operating in synergism with malnutrition, and contributing to an overall poor health status. The role of infectious disease in the collapse was championed by Shimkin (1973), who suggested that Chaga's disease (American trypanosomiasis), Ascaris, yellow fever, and enteric pathogens causing weanling diarrhea may have played a significant role in the deteriorating health of Late Classic popu- Human Biology in the Classic Maya Collapse 167 lations. The only skeletal evidence that directly addressed infectious disease at that time was the diagnosis of treponemal infection in the skeletal remains from Altar de Sacrificios, Seibal, and Zaculeu (Goff, 1953; Saul, 1972, 1973), a condition which Saul rightly did not link to his otherwise bleak view of Maya health. The synergistic interaction of infectious disease with malnutrition is widely recognized as a critical element of weanling diarrhea and subadult morbidity and mortality in disadvantaged populations (Scrimshaw et aL, 1968). Undoubtedly, this process operated among the Maya, as indicated by the prevalence of developmental enamel defects and porotic hyperostosis. We have already examined the role of intestinal parasitism with respect to childhood anemia among the Maya. Infectious disease can also be studied directly in skeletal remains through the investigation of subperiosteal bone inflammation--periostitis--a common response to infection. Disturbance of the periosteal membrane by infectious agents results in the deposition of a thin layer of fibrous new bone on the surface of the existing bone cortex. On recovery from the infection, this new bone is remodeled and gradually integrated into the underlying cortex. Thus, the state of periosteal reactions gives clues to the status of the infection that produced them, be it active or healed. Periostitis occurs in a variety of infectious syndromes including respiratory and enteric diseases, as well as systemic bacterial infections (such as Staphylococcus) and localized infections due to overlying skin trauma (Greenfield and Schorsch, 1967; Ragsdale et al., 1981; Resnick and Niwayama, 1981). Bone responds to infection in a nonspecific manner that does not allow the diagnosis of most infectious agents, so the abundance of periostitis in skeletal samples is often taken as a proxy for infectious disease in general. Analyses of periostitis and porotic hyperostosis in the skeletons of young children have confirmed a strong association between the conditions that support the synergistic role of infection in subadult morbidity and mortality (Lallo et al., 1977; Mensforth et aL, 1978). The infectious agent responsible for periosteal reactions in a skeletal series can occasionally be inferred from their form, and the intraskeletal and populational distribution of the lesions, although it may not be possible to diagnose the specific cause of individual lesions (Buikstra and Cook, 1980; Cook, 1976; Ragsdale et aL, 1981). Periostitis has been systematically studied at relatively few Maya sites. In many cases, the lesions have been noted, but not treated in a manner that permits populational evaluation or differential diagnosis of underlying disease processes. Table II presents summary statistics on the abundance of periostitis on femora and tibiae in Maya series and comparative data from other well-studied skeletal series. Long bone infection occurs at 168 Wright and White Table 11. Frequency of Diaphyseal Periosteal Reactions in Adults in Mayan and Comparative Skeletal Series Femur Tibia Skeletal series % N % N Maya series Pasi6n (combined) 37.3 75 68.0 75 Tipu --8.4 704 Cop~in 43.5 46 55.3 38 Comparative series Moundville, ALa 19.3 419 58.5 434 Gibson, ILa 60.0 45 84.4 32 Ledders, ILa 38.1 21 63.6 22 Ft. Ancient, OH 10.6 160 24.3 136 Jomon, Japan 5.1 332 12.6 324 Medieval York, UKb 13.9 466 61.8 466 Nubia, X-Groupc 3.4 129 --aSeries in which treponematosis has been diagnosed. bSubadult data are included with adult statistics for these samples. CBoth tibial and femoral periostitis considered together. Reference Wright,1994 Cohenet at, 1994 Whittington, 1989 Powell, 1988 Cook, 1976 Cook, 1976 Perzigianet al., 1984 Suzuki,1991 Grauer,1993 Armelagos, 1968 roughly equivalent levels at Cop:in as in the Pasi6n valley sites, with somewhat more than half of adults having tibial lesions (Whittington, 1989; Wright, 1994). Colonial Tipu is very different, with very few skeletons showing periostitis. The difference is likely due to the apparent absence of trep o n e m a l i n f e c t i o n at Tipu ( C o h e n et al., 1994). Lesions typical o f nonvenereal treponematosis have been documented in the Pasi6n series (Saul, 1972; Wright, 1994) and may be present at Cop~in (Whittington, 1989) and Lamanai (Helmuth, personal communication). Maya skeletons show an intraskeletal distribution of periostoses consistent with that of endemic syphilis and yaws. Given the rarity of cranial lesions and the tropical lowland environment, the syndrome may have closely approximated that seen in yaws today (Wright, 1994). It is important to note that the biological cost of endemic treponematosis is not especially high, despite its high visibility in skeletal series (Powell, 1991). The prevalence of periostitis at Cop~in and in the Pasi6n is comparable to that in other nontropical skeletal series with evidence of endemic syphilis, such as MoundviUe (Powell, 1988), and Woodland Illinois (Cook, 1976). Series lacking treponemal infection show substantially fewer periostoses, as among Japanese Jomon peoples (Suzuki, 1991) and ancient Nubians (Armelagos, 1968). We note also that infectious lesions in Medieval York (Grauer, 1993) are as abundant as among the Classic Maya. These patterns highlight the difficulty in comparing skeletal health among populations of differing epidemiological environments but, at the same time, reveal that infectious disease was not anomalous in the Maya lowlands. Human Biology in the Classic Maya Collapse 169 Although treponemal infection might account for the bulk of periostitis at some lowland Maya sites, other infections, in synergism with nutritional stress, undoubtedly contribute to the overall picture. Because parasitic and infectious disease load is dependent on host density, and increased forest clearance with human population density would have reduced alternate nonhuman hosts for vectored diseases in the Classic Period, Santley et al. (1986) argue that infectious disease would have increased toward the end of the Late Classic Period. This hypothesis is not supported by the data from the Pasi6n region, where frequencies of infection remain stable from the Preclassic through Terminal Classic Period, whether sites are considered individually or together. At Cop~in, Whittington (1989) identified a statistically significant decline in the frequency of periostitis between Early and Late Coner phases, which he attributes to a greater risk of infection in the core population than in rural noncore sites, combined with migration out from the core after the political collapse of the Copfin dynasty. He postulates that the decline in periostitis reflects a deterioration of health due to elevated child mortality and thereby the removal of a greater proportion of frail individuals, leaving only robust individuals among the adult skeletal remains. As we noted above, the interpretation of trends in skeletal pathology is complicated by frailty issues. A more traditional interpretation of these data would see the decline as evidence for improved health, a paradox we are unable to resolve at this time. CLASSIC MAYA DIETS: ISOTOPIC EVIDENCE OF SUBSISTENCE CHANGE The Paleodiet Revolution Bioarchaeological investigations have undergone a dramatic advance over the last two decades with the development of methods to examine directly the composition of the diets consumed by prehistoric peoples though chemical analysis of bone. Paleodietary methods provide a direct means of examining consumption on an individual level and, thereby, determining the relationship between diet and health directly. This development allows more explicit testing of bioarchaeological hypotheses regarding subsistence change and the impact of diet on population health and adaptation. The most promising approach exploits systematic isotopic fractionation of carbon and nitrogen atoms at each trophic level in the foodweb. While the stable isotopes of an element have identical chemical properties, their natural distribution is, in part, governed by kinetic effects of mass differences. Isotopic ratios, measured relative to a known standard, are given as -30 ' ' -25 C3 N2-fixing plants C3 plants {f.w. snail meat freshwater fish meat 613C (%. PDB) -20 i terrestrial herbivore meat i -15 mollusc meat reef -1o i C A M & C 4 plants reef fish meat ~ i 5 Fig. 2. t~otopic composition of the edible portions of Mayan foods. Carbon values have been corrected for anthropogenic enrichment in --C to estimated Classic Period values. Food values were compiled from data of Wright (1994) and Tykot el al. (in press). -35 0 ,t 6 2; Lm 8 g 10 12 14 g i ~. 0 Human Biology in the Classic Maya Collapse 171 the 8 ratio of the heavier to the lighter isotope. For carbon, the ratio 13C/12C, or ~513C,is calibrated relative to Pee Dee Belemnite (PDB), a marine limestone; likewise for nitrogen, the ratio 15N/~aN, or ~515N,is calibrated relative to atmospheric N2, air. Because the isotopic compositions of foods are passed on to the tissues of consumers in a characteristic manner, we can reconstruct prehistoric diets from the isotopic signature of archaeological skeletons (Ambrose, 1993; DeNiro, 1987; Schwarcz and Schoeninger, 1991; van der Merwe, 1982). Although specific proportions of menu items cannot be precisely identified in complex diets, the stable isotopic composition of bone can characterize the relative contributions of the primary dietary components. This method constitutes the most accurate means to examine prehistoric food consumption available at this time. Figure 2 illustrates the isotopic composition of most foods available to the ancient Maya. The stable isotopes of carbon are differentially incorporated into plant tissues during photosynthesis because of enzymatic diff e r e n c e s in CO2 fixation. Plants using the Benson-Calvin or C3 photosynthetic path have a tissue ~13C near -27%0, relative to PDB. Dramatically more enriched, or heavier values occur in plants using the HatchSlack or C4 pathway, which average -13%o (O'Leary, 1988). In the Maya area, most wild plants and cultigens employ C3 photosynthesis and have light isotopic values, including beans, squash, roots, and fruits. The most important exception is maize Zea mays, which uses the C4 pathway and is enriched in the heavier isotope, 13C, so carbon isotopes can be used as a proxy for maize consumption in the Maya area. To our knowledge, amaranth Amaranthus spp. and epazote Chenopodium ambrosoides are the only other C4 plants that might have contributed to the Maya diet. A third group, using the Crassulacean acid metabolism (CAM) pathway, often resembles C4 isotopic signals but may have lighter values depending on variable use of daylight photosynthesis. CAM plants that might confound with maize signals in the Maya paleodiet include the nopal cactus Opuntia, the pifiuela Bromelia karatas, and possibly the pineapple Ananas cosmosus, but may not have been extremely important to the diet. Carbon from animal protein would also contribute to enriched signatures in carnivorous diets due to trophic enrichment in protein metabolism, but pass on the dietary preferences of the herbivore consumed. Most terrestrial fauna in the Maya area consumed wild C3 flora (or lived in C3based foodwebs), but isotopic evidence confirms that some animals have C4-1ike signals, such as dogs, which were regularly fed or scavenged C4 foods (probably maize) (Tykot et al., 1996), and occasional deer and peccary, which are known to feed at the margins of maize fields (White and Schwartz, 1989; Wright, 1994). Marine fish from the Caribbean have an enriched carbon isotopic content similar to that of maize (Keegan and 172 Wright and White DeNiro, 1988; Tykot et al., 1996) and could confound the signature unless used in conjunction with nitrogen isotopes, but freshwater Petdn fish resemble C3 plants in ~13C (Wright, 1994). Likewise, marine mollusks are more enriched in ~13C than are freshwater snails from the Pet6n (Tykot et al., 1996; Wright, 1994). Nitrogen isotopes do not differ dramatically between plant types, although legumes such as beans, Phaseolus vulgaris, contain symbiotic bacteria that fix atmospheric nitrogen thus have a 515N near 0%0, slightly lower than other plants with a ~lSN near 2-5%o. Nitrogen isotopes are particularly useful as indicators of the trophic position, because 15N is fractionated at each level of the foodweb, with consumers having ~lSN about 3%0 heavier than the food they consume (DeNiro and Epstein, 1981; Schoeninger, 1985). In the Maya area, marine fish are not as enriched in 15N as in boreal waters (Keegan and DeNiro, 1988) but would raise the consumer ~15N more than the consumption of terrestrial protein. Likewise, freshwater fish are even more enriched in 15N, and their consumption would raise the ~15N disproportionately (Wright, 1994). Stable isotopic analysis has generally made use of collagen--the organic portion--in archaeological bone, and the isotopic data obtained from the Maya area to date are principally collagen data. Recent advances have focused on ~13C in bone apatite--the inorganic portion--and the differences between collagen and apatite ~13C. At this time, most paleodiet researchers concur that dietary protein is preferentially routed to synthesis of collagen, so collagen data should be interpreted with some bias toward the protein component of prehistoric diets. In contrast, carbon atoms in bone apatite seem to be drawn from the total dietary pool of all nutrients ingested (Ambrose and Norr, 1993; Krueger and Sullivan, 1984; Lee-Thorp et al., 1989; Tieszen and Fagre, 1993). Hence, apatite values may be more indicative of agricultural foods than collagen, which would include both plant and animal proteins. Work currently under way in both our laboratories on apatite of Maya skeletons (see also Coyston, 1994; Gerry and Krueger, 1997; Wright and Schwarcz, 1996) may modify the trends that we review here, which are based on the ample collagen data currently available from the Maya Lowlands, Paleodiet of the Ancient Maya To date, isotopic techniques have been used to investigate paleodiet at 14 Classic Lowland Maya sites, located primarily in Belize, Pet6n, and the southeastern region (Fig. 1). To our knowledge, no isotopic work has yet been undertaken in the Northern Maya Lowlands, and only one high- 6 -14 7 8 ' | -12 I -13 i ~ , i -t0 , i -9 i, i -8 i , I- + T-II 613C (%0 PDB) -11 I I . .k I-7- i -7 , -6 Lamanai Pacbitun Barton Ramie Baking Pot Holmul Uaxactun Altar de Sacrificios Seibal Dos Pilas Aguateca Itzltn [] Cop/m V Mojo Cay ,I. Iximch~ [3 9 O A @ 9 9 O [] II 9 Fig. 3. Mean isotopic composition of human collagen at Maya sites. Error bars represent one standard deviation to either side of the mean. Data are taken from various references cited in Table IlL In the center of the graph, mean values for Holmul, Seibal, and Aguateca are nearly coincident. Z 9 lq 11 12 o_ la ~~ r O gg gl 3I J = 174 Wright and White land site has been examined. All of these projects have shown that ancient Maya diets relied heavily on maize agriculture from Preclassic times on. However, a substantial degree of geographic, temporal, and social variability in isotopic results indicates considerable diversity of dietary strategies among the ancient inhabitants of the Maya Lowlands. Geographic Patterning Figure 3 illustrates the mean values obtained at a number of sites. Table III lists the mean values and number of individuals sampled by site. These data include all chronological periods from which skeletons have been sampled, and are not controlled for social status or sex. We discuss chronological and social variability further below. In the ensuing interpretation of diet compositions we generally assume that the bulk of foods consumed at any given site was also cultivated or collected locally. Although trade of foods was documented in the Colonial Period (Roys, 1943), it is likely that imported foods provided a relatively minor proportion of nutrients ingested and were perhaps limited to occasional elite delicacies, such as fish (Lange, 1971). Bulk transport of basic staples has been proposed for some regions, especially the Central Pet6n (Sanders, 1973; Harrison, 1990), but little evidence can be marshalled to document this. On the contrary, the local specificity of trace elemental dietary signatures in the Pasi6n region provides a strong case that most foods were obtained locally (Wright, 1994; 1995). With the exception of Lamanai, which shows a large shift over time, a broad distinction can be drawn between the isotopic composition of collagen from Belizean versus inland Pet6n sites (Gerry and Krueger, 1997). Preclassic and Classic Lamanai (White and Schwarcz, 1989), Baking Pot, Barton Ramie (Gerry, 1993), and Cuello (Tykot et al., 1996) differ from Pet6n sites in showing much lighter carbon isotopic signatures. This result presumably indicates that maize agriculture was substantially less important to local diets at the Belizean sites than in the Pet6n. Sites farther inland show more 13C enriched collagen, as at Altar, Seibal, Dos Pilas, Itzfin, and Aguateca (Wright, 1994). Likewise, Pacbitun (White et al., 1993) and Holmul show enriched "Pet6n" signatures (Gerry, 1993). Uaxactun clusters with the Belizean sites (Gerry, 1993). Although differences in 813C have traditionally been interpreted in terms of variation in maize consumption, recent data and interpretations of isotopic metabolism ~ggest that discrepancy in faunal consumption may be involved. Since dietary protein contributes preferentially to collagen synthesis, animal foods may be as important as maize in defining the ~513C, Lamanai Pacbitun Barton Ramie Baking Pot Holmul Uaxaetun Altar de Sacrificios Siebal Dos Pilas Aguateca Itzan . Copan Mojo Cay Iximche Site -10.84 -9.86 -11.24 -11.03 -9.38 -10.65 -9.4 -9.4 -9.05 -9.56 -9.17 -9.26 -8.46 -7.78 Mean 2.37 1.39 1.42 1.11 1.27 1.09 1.37 1.16 0.98 0.69 0.30 0.72 0.38 0.40 SD 50 17 38 9 14 6 38 34 19 8 5 46 8 13 N 9.81 9.32 8.8 9.2 9.3 9.4 8.6 9.39 9.57 9.35 7.96 7.56 10.13 7.92 Mean 0.89 0.67 0.44 1.34 0.84 0.97 1.02 0.97 1.05 1.16 0.98 0.48 0.92 0.40 SD 47 17 38 9 15 5 38 34 19 7 5 46 8 13 N Reference White and Schwarcz, 1989 White et al., 1993 Gerry, 1993 Gerry, 1933 Gerry, 1993 Wright, 1994 Wright, 1994 Wright, 1994 Wright, 1994 Wright, 1994 Wright, 1994 Reed, 1994 Norr, 1991 Whittington and Reed 1992 Table III. Mean Isotopic Compositions of Human Bone Collagen at Maya Sites i 813C 815N 9- ~~ 9. m 3 176 Wright and White despite a smaller proportion to the total diet. Freshwater fish are about 5%o lighter than terrestrial herbivores in the Maya Lowlands (Wright, 1994), so populations consuming more fish than terrestrial meat would have a lighter ~13C, even with equal maize consumption. It may be revealing to note that the Belizean sites with a light ~513C are all located in riverine environments. In contrast, the site of Pacbitun shows an enriched "Petdn"like 813C (White et al., 1993), although it is farther east than the riverine, light-513C sites Barton Ramie and Baking Pot (Gerry, 1993). Unlike the riverine Belizean sites, Pacbitun is located inland and would not have had direct local access to sustainable freshwater fish populations. Moho Cay, at the mouth of the Belize River, also stands out from the generally light Belizean sites, having an enriched fi13C value similar to that of the Petdn sites (Norr, 1991). However, its maritime location, faunal assemblage, and slightly enriched ~15N of collagen reveal that the consumption of marine fauna contributes to the high fi~3C of the collagen. Among Petrn sites, less variation is evident among riverine and "inland" sites. Inhabitants of Holmul (Gerry, 1993) had less local access to surface river fauna, but light 513C values are not observed at riverine sites in southwestern Petrn either--Altar de Sacrificios, Seibal, Aguateca, and Itz~in (Wright, 1994). It is unclear why Uaxactun should resemble Belizean sites more than other Petdn sites, but since all skeletons sampled were from Structure A-V, an elite "palace," and most are female (Gerry, 1993), a social or sexual distinction may be at play. As yet, we have no data on lacustrine populations from the Central region. The 13C-enriched collagen of Pet6n sites is probably due to greater maize consumption. However, protein from C4 plant-consuming animals such as deer, peccary, and dogs may also contribute to the collagen signal. The 515N of Petdn human collagen is more enriched than that of herbivores, falling into the range of terrestrial carnivores, thereby indicating substantial meat consumption (Wright, 1994). In the southeastern region, paleodiet has been studied only at Cop~in, which shows a generally "Petdn"-like 613C-enriched signature (Gerry, 1993; Reed, 1994). However, the filSN is substantially lighter than collagen from any other Maya site, falling squarely in the realm of herbivorous mammals. This result implies that animal protein was less important to ancient Cop~n diets than at other sites. If faunal meat contributes less to the enrichment of ~13C, then maize reliance may have been greater at Cop~in than elsewhere. Cop~n is located at about 600 m asl, a higher elevation than the lowland Petdn and Belize sites examined (20 to 250 m asl). Instead of diverse broadleaf forest, the hills surrounding the Cop~in Valley support pine forest, an environment very different from that of the Pet6n. This marked ecological distinction, undoubtedly tied to differences in the diversity and abundance of wild game, may have Human Biology in the Classic Maya Collapse 177 had a more profound role in shaping Copfin diets when compared with the Pet6n than social factors such as population density, although the two issues are difficult to separate. It is interesting to note that Late Postclassic highland Iximchd collagen also shows a quite low 515N, although it is slightly more enriched than at Copfin. Despite Iximchd's much higher elevation (2200 m asl), ecologically it resembles Copfin more closely than the lowland sites, so the comparable nitrogen data support the suggestion that environmental parameters contribute to the distinction of Copfin 515N. Altitude has a direct impact on ~13C values in flora, so collagen is more enriched in 13C at Iximch6 than elsewhere, which should not be taken as evidence for greater maize reliance (Whittington and Reed, 1994, 1996). Chronological Patterns Attention has been drawn both to the bulk composition of Maya paleodiets as evidence for an environmental stimulus for the collapse (Reed, 1994) and to regional variability in isotopic data as evidence against it (White et al., 1993). The role of dietary factors in the collapse will be most securely evaluated through investigation of chronological patterns in consumption that are implicated as causal mechanisms of nutritional deterioration in the ecological model. Table IV contains a s u m m a r y of chronological trends in 813C and ~15N at various sites. The first attempt to study Maya diet with isotopic techniques revealed the most extreme chronological shift documented to date (White, 1986; White and Schwarcz, 1989). However, it is difficult to interpret the Lamanai data in terms of subsistence implications for the collapse since the community prospered through to historic times. Lamanai collagen had 513C comparable to CueUo in the Preclassic (-12.5%o) and which declined during the Classic Period to a low of-15%o in the Terminal Classic Period. During Postclassic and Historic times, 813C increased dramatically to a "Pet6n"-like value of -9.5%0 (White and Schwarcz, 1989). Although increasing maize dependence is certainly the primary factor behind this ~13C transition, a shift from consumption of freshwater fish to marine fish in the later period could contribute to the 813C shift. An increase in consumption of maize-fed anim a l s - s u c h as turkeys, which were first domesticated in the Postclassic (Hamblin, 1984)--is also a possible factor. A Postclassic shift toward marine foods would also be consonant with changing trade and regional interaction networks at this time, which shifted from southwestern overland interaction with the Petdn, to north and eastern interaction with Yucatan and the Belizean cays via maritime trade (Pendergast, 1986). 178 Wright and White Table IV. Chronological Trends in ~13Cand 815N of Collagen from Classic Maya Skeletons 813C Site & period Mean SD Lamanaia Historic -9.9 0.9 Postclassic -9.3 0.8 Terminal Classic -15.0 1.2 Late Classic -14.2 1.1 Early Classic -12.3 1.6 Preclassic -12.7 0.0 Pacbitun b Terminal Classic -10.63 1.5 Terminal Classicc -9.9 1.4 Late Classic --8.5 1.3 Early Classic -9.2 -Altar de Sacrificiosa Terminal Classic -9.0 0.9 Late Classic -8.3 1.0 Early Classic -9.1 0.5 Preclassic -10.4 0.6 Dos Pilasa Terminal Classic -9.4 0.8 Late Classic -9.0 1.0 Seibala Terminal Classic -9.4 1.2 Late Classic -9.4 1.4 Preclassie -9.6 1.0 aData from White and Schwarcz (1989). bData from White et al. (1993). CControUed for status, age, and sex variation. dData from Wright (1994). 815N N Mean SD N 10 24 7 3 4 2 9.7 9.5 9.9 10.3 10.9 10.2 0.6 0.9 0.4 0.1 1.5 0.6 9 24 6 2 4 2 18 8 3 1 9.3 9.2 9.3 8.1 0.7 0.6 0.6 -- 16 8 3 1 16 7 5 8 8.8 9.0 8.2 8.4 1.1 1.0 0.6 0.7 16 7 5 8 4 14 8.8 9.8 1.2 0.9 4 15 16 11 7 8.9 9.9 9.7 0.9 0.9 0.8 16 11 7 Less d r a m a t i c t r e n d s are s e e n at sites f a r t h e r inland. A t P a c b i t u n , the s a m p l e o f L a t e Classic burials s t u d i e d isotopically is small b u t c o n f i r m s a statistically significant decline in 613C b e t w e e n the L a t e a n d t h e T e r m i n a l Classic o c c u p a t i o n s ( W h i t e et al., 1993). T h i s is a c c o m p a n i e d by a slight n o n s i g n i f i c a n t i n c r e a s e in ~15N. This t r e n d is p a r a l l e l e d at two sites f r o m t h e s o u t h w e s t e r n Pet6n. A t A l t a r d e Sacrificios, 613C i n c r e a s e d f r o m P r e classic t h r o u g h L a t e Classic times a n d t h e n d e c l i n e d slightly in the T e r m i n a l Classic p o p u l a t i o n (Wright, 1994, 1997). N i t r o g e n i s o t o p e s r e m a i n e d s t a b l e t h r o u g h o u t t h e A l t a r s e q u e n c e , implying stability in m e a t p r o c u r e m e n t syst e m s a n d t h a t the 6t3C t r e n d s a r e d u e to shifts in t h e relative i m p o r t a n c e o f m a i z e versus C3 plants. A t D o s Pilas, a few burials f r o m t h e s m a l l postc o l l a p s e o c c u p a t i o n show slightly lower 813C t h a n t h e L a t e Classic p o p u lation, p a r a l l e l i n g the t r e n d at A l t a r (Wright, 1994, 1997). Human Biology in the Classic Maya Collapse 179 A very different pattern is found at Seibal, where the 513C is stable over the full sequence from Late Preclassic through Terminal Classic times. It is revealing to note that Preclassic Seibal diets differ significantly from their contemporary neighbors at Altar, having a much more enriched ~513C and ~15N, a fact which demonstrates that cultural as well as environmental conditions shaped the ancient diet (Wright, 1994, 1997). In the face of chronological stability in 513C at Seibal, ~515Ndeclines from Late to Terminal Classic Periods. At Seibal, the nitrogen isotopic composition of collagen differs from other Pasi6n sites in being significantly more enriched, so the decline in ~51SN,which brings Terminal Classic values into line with neighboring sites, may be due to a shift from emphasis on aquatic to terrestrial fauna, rather than a decline in absolute meat consumption, a trend also implied by Sr/Ca and Ba/Ca levels in bone mineral (Wright, 1994). In sum, these data confirm that prehistoric diets did vary in concert with major events in Maya history. However, all sites do not show an equivalent subsistence reaction with the impending collapse. Santley et al. (1986; Santley, 1990) argue that maize consumption rose with increasing population density and environmental degradation. This idea found some support in pollen data from Central Petdn (Wiseman, 1985), that are now in doubt due to more recent paleolimnological work (Brenner et al., 1990). A Terminal Classic increase in maize production is not supported by isotopic data for maize consumption at any site. In fact, if any trend is apparent, it is toward declining maize consumption in the final occupations at Pacbitun, Altar, and possibly Dos Pilas. Indeed, the Terminal Classic decline in 813C at Pacbitun is interpreted as support for an ecological model of collapse at this particular site (White et al., 1993). Because the Terminal Classic is the period of greatest population density and investment in agricultural intensification at Pacbitun, White interprets the isotopic data to mean that maize production capacity was at its limit and that inhabitants were forced to find alternate C3 foods. This interpretation does not fit so well for Altar de Sacrificios and Dos Pilas, however. In both cases, the Terminal Classic occupation postdates the collapse of the elite authority structure. At these two sites, as at Pacbitun, Terminal Classic collagen is slightly more depleted in laC than in the preceding Late Classic Period, indicating a decline in maize consumption. While the population remained sizable at Altar, it was very much reduced at Dos Pilas, so larger yields of maize relative to the smaller population should have been attainable. If agricultural production had reached a critical threshold in the Terminal Classic Pasi6n, we would expect carbon isotopic shifts at Seibal, where Terminal Classic population density was greatest and elite political authority maintained longest, but these do not occur. 180 Wright and White Why then did maize consumption decline at some sites? We can envision two scenarios that might lead to declines in total maize production and, thereby, consumption. (1) Degradation of the agricultural landscape by overworking could remove land from production as posited in ecological models of collapse, thereby lowering total yields of maize. Such agricultural failure would also affect the capacity for production of C3 foods, however, resulting in a deficit of all agricultural and wild foods. Therefore, this scenario implies a state of Widespread and calamitous undernutrition, which as reviewed above, is not supported by the paleopathological data. (2) Sociopolitical turmoil at the end of the Classic Period shifted the role of elite authority away from subsistence concerns, leaving agricultural decisions more firmly in the hands of local autonomous farmers or to a decoupling of dietary behavior from state ideology. Certainly maize symbolism was a critical element of Classic Maya ideology. The relationship between religious iconography and agricultural practice is presumably a reinforcing cycle, and the possibility that high maize consumption was partly accentuated by the ideological role of this cultigen should not be ignored. Moreover, tribute or taxation that was paid with agricultural produce must have influenced the mix of crops planted by farmers, thereby shaping the diets of the populace at large. Changes in the role of elites in agricultural management are likely to be variable as the extent of state involvement in agriculture may not have been consistent across the ancient Maya landscape and from polity to polity. As direct measures of diet, the isotopic data might already be revealing indirect evidence of varied state interests in agriculture or, alternately, state activities which affect food economy. For example, maize consumption at Lamanai is lowest during the Terminal Classic Period, which might be taken as evidence of agricultural failure, were it not for the fact that intensive political and economic activity is simultaneously indicated by the construction of substantial monumental architecture. White (1986) interpreted this combination of facts to mean that either trade patterns in foodstuffs changed significantly or, more likely, the elite were exercising a labor tribute which had a high cost for maize production. Farmers may not have been able to meet the labor demands of both monumental construction and intensive agriculture at the same time. For long-term survival of the Lamanai polity, the economic shift was a successful strategy. Diet may have been affected by decisions of state rather than by environmental limits. Moreover, this dietary shift implies the ready availability of alternate foods. Although it is tempting to align changes in maize consumption with agricultural success, we must remind ourselves that maize may be replaced by other cultivated crops, not only by recourse to foraging of wild foods. Human Biology in the Classic Maya Collapse 181 Social Patterns Political control over the food economy can also be reflected in status differences in diet within a population. As Fried (1967, p. 186) noted, we anticipate that high-status individuals had privileged access to "the basic resources that sustain life." The identification of status groups within ancient Maya populations is a thorny issue. Social distinctions can be identified through settlement patterning, architectural complexity, artifact distributions, and mortuary remains. For integration with paleodietary data, burials provide individual assessments of status that hold the most promise. Although recent work is beginning to address the social implications of Maya funerary behaviour (McAnany, 1995; Chase and Chase, 1989, 1992; Wright, 1994), interpretation of Maya burial programs often lacks the theoretical sophistication of mortuary archaeology in other world areas (e.g., Bartel, 1982, Beck, 1995; Chapman et al., 1981; O'Shea, 1984; Tainter, 1978). A comprehensive consideration of status distinctions in diet among the Maya would require detailed evaluation of these issues and is beyond the scope of our review, but we briefly summarize findings to date as these may bear on the collapse. Social distinctions in diet were first identified at Lamanai. The highstatus Early Classic tomb individuals there consumed the least maize and may have had privileged access to reef resources (White, 1986; White and Schwarcz, 1989). Subsequently, social variability in diet has been documented at Copan, Pacbitun, and among the Pasi6n sites. At Copan, Reed (1992, 1994) notes greater isotopic variability in skeletons interred in architecturally elaborate "high-status" domestic groups than in "low-status" residences. He interprets this to indicate that high status Copanecos had access to a broader array of food resources, but it could also be taken to mean that "high-status" groups contain burials from a broad range of social strata--including slaves--whose diets differed. At Pacbitun, settlement and architectural evidence confirms continued elite activity in the early part of the Terminal Classic Period. Isotopic data imply social distinctions in diet among different grave types during Late and Terminal Classic times and suggest that maize was preferentially consumed by elites in the site core at the expense of commoners in the periphery, who ironically must have been directly involved in its cultivation (White, 1997; White et al., 1993). Unfortunately, it is not possible to compare the extent of status differences in diet between the two periods because of sampling limitations. White argues that increasing divergence in maize consumption between status groups over time could suggest environmental constraints on maize production as it becomes an increasingly 182 Wright and White valued social commodity. This may have been occurring at Terminal Classic Pacbitun. In contrast, during the Late Classic Period at Dos Pilas and Altar de Sacrificios, isotopic differentiation in both fi13C and 815N occurs among social subgroups identified through multivariate analyses of mortuary variables. With the exception of 15N enrichment in the highest status group at Altar, these patterns indicate a more complex pattern of dietary partitioning than that between grave types at Pacbitun. At no site in the Pasi6n region is fi13C tightly linked with mortuary status in a simple unilineal scale, indicating that maize cannot be singled out as a socially valued food here. Indeed, among Terminal Classic Altar and Seibal burials, social heterogeneity in diet is diminished, so competition over resources does not provide any indication that food sources were limited but, rather, implies a social transformation that occurred in concert with political disintegration (Wright, 1994, 1997). In a broad series of burials from across the lowlands, Gerry (1993) found that regional stable isotopic paleodietary differences overshadowed social distinctions. He argues that diet did not vary between status groups defined by mortuary features, a conclusion contradicted by the studies reviewed above. Social differentiation in this analysis, however, may be obscured by the long chronological span and broad geographic spread of his burial series. Mortuary symbols are prone to social manipulation and cannot be assumed to have had universal referents over prehistoric Maya time and space. Indeed, mortuary symbols do not covary uniformly even among neighboring Pasi6n sites (Wright, 1994), and burial goods exaggerate status distinctions at some sites in Belize (Chase, 1997). DISCUSSION AND CONCLUSION Ecological explanations of the Classic Maya collapse have been examined in light of evidence from human skeletal biology and isotopic dietary reconstruction. We have questioned a number of the assumptions of these models, in particular, their occurrence as a pan-Maya phenomenon, and the necessary inclusion of nutritional and pathology submodels. At the outset of this paper, we raised several concerns about the appropriate use of analogy from modern agricultural practices, diet, and health to the Prehispanic context. In turn, the evidence from human skeletal biology and isotopic reconstruction reviewed here sheds further doubt on the accuracy of ecological models of collapse as commonly constituted. Here we have examined paleopathological and paleodietary data largely independently, although these issues are typically subsumed within a single model. Human Biolo~, in the Classic Maya Collapse 183 Osteological evidence for the nutritional argument is particularly problematic and contradicts the expected trends. In contrast, dietary expectations are less straightforward. While the isotopic record does not provide consistent support for the broader ecological model, environmental pressures may have contributed to dietary change at some sites. We outlined three critical issues for paleopathological data as central to the integrity of ecological models of collapse. If the nutrition and health arguments are to be upheld, the skeletal remains must demonstrate (1) that health was more severely compromised than among other civilizations that did not collapse, (2) that health deteriorated over the span of Classic Maya history, and (3) that ancient Maya subsistence choices had a direct and negative impact on the health of the population. Although comparison of skeletal data between sites and cultures in differing epidemiological contexts is fraught with difficulty, consideration of the data in a global perspective does not support the generally held assumption that the Maya suffered anomalously high levels of disease. Comparable levels of anemia, infection, and dental growth disruption can be found in both urban and less hierarchically organized agricultural societies from a variety of world regions. At this time, there are no published data which provide unequivocal support for a change in health burden over Classic Maya history at any lowland Maya site. Several avenues of investigation do support health changes between the Classic and the Postclassic periods (White, 1986) and in concert with the arrival of Spanish conquistadors. Colonial populations differ from prehistoric ones in terms of stature (Danforth, 1994), infectious disease (Cohen et al., 1994; White et al., 1994; Wright, 1990), and the timing of childhood growth arrest (Danforth, 1989), all trends which highlight several problems with the use of modem analogy in interpretation of ancient Maya health. The correlation of dietary and pathological data provides some indication that dietary choices had health consequences. This is evident in some 9parallel trends between the expression of anemia and ~13C, but these trends are not regionally consistent and the role of parasitism in anemic expression merits further investigation. Given the frequency with which we are confronted by statements about the severity of disease among the Maya, we expect that some of our coLleagues will be surprised by the conclusion that the Lowland Maya did not suffer an anomalous health burden and that health was largely stable over the Classic Period. Such epidemiological arguments have become almost axiomatic in discussions of Maya paleoecology, despite the scant evidence from which they were drawn. Uncritical acceptance of these arguments is due in part to an understandable tendency to interpret prehistoric health 184 Wright and White by reference to modern conditions in the tropics. This analogy, though not inappropriate, suffers from exaggeration of the differences between temperate and tropical epidemiology. Discussions of disease in the Maya area highlight tropical diseases that are absent from temperate zones (e.g., Shimkin, 1973). Many of these diseases are familiar to archaeologists as perils of fieldwork. The lowland jungles have been characterized as a "green hell" (Drucker and Fox, 1982), plagued by extremely abundant pathogens far different from those we encounter in our comfortable temperate homes. Santley et al. (1986) note that the tropics are home to more species of potentially harmful organisms than are temperate regions. But is the tropical forest environment especially unhealthy? Rather than a high abundance of noxious pests, the distinguishing feature of tropical forests is their extremely high species diversity. Hand in hand with the large variety of species present, the abundance of each species is much less than in low-diversity temperate areas. That is, populations are thinly and patchily distributed (Janzen, 1983). For pathogens this is an extremely important issue. While a great variety of parasitic organisms may be found in tropical forests, the risk of contracting a given infection is proportionately lower. Santley et al. (1986) are correct in noting that today the burden of illness is greater in the tropics than in temperate zones. However, in the tropics the major diseases causing illness.., are frequently not the exotic parasitic diseases usually associated with tropical medicine, but are primarily bacterial and viral infectious diseases that once were endemic in industrialized countries but now are controlled through improvements in immunization, hygiene, nutrition, housing, water supply, and socioeconomic status . . . . (Walsh, 1990, p. 195). That is, the perception of tropical forests as disease-ridden is biased by recent improvements in health care in temperate, developed nations. We do not mean to imply that the eighth-century Southern Lowlands were epidemiologically equivalent to a pristine tropical forest. Dramatic forest clearance would have reduced the abundance of some parasites by destroying habitats of normal faunal hosts, such as monkeys in the case of yellow fever. Others would increase with human population density, especially hookworm, intestinal helminths, and roundworms. These may be responsible for the high prevalence of porotic hyperostosis on Maya crania. As in temperate environments, bacterial and viral infections would have been dependent on both population density and hygiene. We concur with Santley et al. (1986) that the prehispanic Americas were not a disease-free paradise, but neither should the impact of Old World pathogens on modem health be underestimated. Many of the diseases that may now be contracted in the Maya Lowlands were not present prehispanically. The most obvious of these is malaria, Plasrnodium vivax, Human Biology in the Classic Maya Collapse 185 which arrived from Africa in the sixteenth century aboard Spanish galleys and poses the most omnipresent health hazard in modern Pet6n. Along with the well-documented diseases smallpox, measles, and typhus, an unidentified number of bacteria and viruses also accompanied the Spaniards (in both directions of their voyages). We are hard pressed to identify these today, because most were not medically identified until this century and therefore lack historical records. Nutrition and health did play an integral role in Maya culture and paleoecology, but we must beware of laying too much blame on biological factors for the events of Maya history, unless rigorous data can be marshaled. At this time a firm connection cannot be drawn between the paleopathological data and the fate of ancient Maya cities. Isotopic paleodietary data are relevant to both health and subsistence issues. Assuming the central tenet of ecological models--that environmental degradation removes land from agricultural production, thereby reducing the availability of all cultivated foods, especially maize--the dietary argument can only be upheld by (1) consistent change in isotopic composition of diets into the Terminal Classic Period, (2) changes in the social distribution of foodstuffs with valued foods increasingly canalized to highstatus individuals, and (3) a correlation among diet and nutritional disease, growth disruption, and infectious disease. With respect to 1, as the Classic Period population density rose, the traditional model argues for increasing reliance on maize, due to its high productivity, to maintain adequate food supply (Santley, 1990, p. 329). A concomitant drop in the consumption of wild faunal meat is expected, due to the diminution of uncultivated forested habitats. This should be shown by the increasing 613C and decreasing 815N of bone collagen (Wright, 1994, 1996). Alternately, if agricultural failure precludes increased maize production at the expense of other cultigens, and adequate forest or fallow land remains for the collection of wild resources that had previously not been intensively exploited, then a decline in 513Cmight signal agricultural stress (White et aL, 1993; White, 1996). This second scenario requires decoupling the dietary transition from health problems generally posited to be the agent of collapse. The possibility that agricultural intensification switched to highly productive C3 root crops (Bronson, 1966) seems unlikely in view of the scant paleobotanical evidence for tubers. Moreover, at Lamanai declining caries frequencies correspond to the drop in Classic Period ~13C (White, 1994), a finding inconsistent with heavy consumption of starchy roots. Isotopic dietary data from bone collagen do not provide consistent support for dietary transitions that would corroborate either of these propositions. The current dietary record from 14 regionally diverse sites indicates 186 Wright and White considerable variation in the amount of maize, C3 plants, and animal foods consumed by the ancient Maya. During the Terminal Classic, maize consumption neither increases nor declines consistently across the Maya Lowlands. Nor is there support in filSN trends for the proposition that animal protein became limited. Although a few sites show comparable declines in Terminal Classic maize consumption, differing sociopolitical and demographic contexts preclude consistent interpretation of the trends. Likewise, dietary privileges with social status appear to have been independently constituted across the Maya Lowlands. Although maize may have become more valued in the final occupation at Pacbitun, dietary partitioning is reduced at Altar and Seibal. As noted above, we have yet little data that adequately tie pathological conditions to individual diets or confirm a causal relationship between dietary strategy and biological health. Geographic patterning in paleodiet indicates that environmental factors were important in shaping Maya diets (Gerry, 1993). Sites in Pet6n show more enriched 813C signatures, indicating greater reliance on maize and terrestrial herbivores than do riverine sites in Belize, where a broader spectrum of C3 plants and probably freshwater fauna was available. Lower environmental diversity in the pine-forested Copfin area compared to the rain forests of Pet6n and Belize likely accounts for the lower ~ISN and the inference of greater maize consumption there. Despite these broad ecological differences, the variable trajectories of site-specific diets over time within a single region appear to have been conditioned more by sociopolitical transitions than environmental constraints. The absence of consistent trends in paleopathological indicators and dietary composition compels us to reject ecological models wherein diet and health stresses are cited as key factors to account for the abandonment of so many sites in the Southern Maya Lowlands. This is not to say that environmental and population pressures could not have contributed to sociopolitical instability. Human biological data are best suited to evaluate long-standing and gradual trends, because skeletal changes better record chronic than acute illness, and stable isotopes in collagen average diet over many years. Thus, a dramatic and sudden shift in health--on a scale of 5 years or less--might not be biologically detectable. Moreover, archaeological chronology is insufficiently precise to pinpoint such rapid change in most aspects of cultural or biological history. Abrupt abandonment has been documented for several sites in the Petexbat~n region (Demarest and Houston, 1989, 1990; Demarest et al., 1992, 1991; Inomata, 1995; Vald6s et al., 1993) but is securely linked to political rather than ecological factors. Elsewhere, evidence for rapid depopulation following political decay is rare. For instance, a sizable population r e m a i n e d at Altar de Sacrificios after the decline of elite Human Biology in the Classic Maya Collapse 187 architectural activities (WiUey, 1973). Although Terminal Classic population did drop substantially in the Central Pet6n, significant continuity in settlement and ceramic systems has been found in the Lake region (D. Rice, 1986; P. Rice, 1986). Depopulation of the Cop~n valley is argued to have been exceedingly protracted, with dense rural settlement outlasting the political core by several centuries (Webster et al., 1992; Fash and Sharer, 1991; cf. Braswell, 1992). Moreover, ecological accounts of the collapse typically argue for a gradual deterioration of the agricultural landscape and of health over time (Santley et aL, 1986; Culbert, 1988; Willey and Shimkin, 1973). Recent paleoclimatic work on sediment cores from Lake Chichancanab in Quintana Roo documents a shift in the stable oxygen isotopic composition (8180) of lake gastropods and ostracods, which is thought to correspond to a period of climatic drying near A.D. 800-1000 (Hodell et al., 1995). The timing of this event raises the possibility that climatic change might have played a role in the collapse. Sabloff (1995) suggests that this drying event might have precipitated rapid environmental degradation or inhibited recovery of stressed agricultural systems in the most densely populated areas. Health implications of such a shift are unclear. Elimination of pools of standing water would reduce breeding grounds for some pathogens, but encourage greater utilization of restricted water sources by more people, elevating the probability of contamination. It is important to note that these data are from the Northern Lowlands, where water is more critically limited than in the Southern Lowlands, yet the drying trend is coeval with the growth of Northern cities such as Sayil, Uxmal, and Chichen Itza. As Hodell and co-workers (1995) state, the implications of the Chichancanab isotopic data are unknown for the other parts of the Maya area, and the impact of such a drying trend would be highly variable across the lowlands given the diversity of microclimatic patterns. The documented 5180 shift averages about l~ which could correspond to a relatively slight change in mean temperature or rainfall or both. However, the complex relationship between 5180 of aquatic fauna and lake evaporation does not permit easy calculation of the magnitude of climate change. This shift should not be construed as evidence for "drought" per se (cf. Sabloff, 1995). Although the evidence for climatic drying is convincing as presented, a consideration of diagenetic alteration of the shell carbonate--as with isotopic study of bone apatite in the Maya area (Wright and Schwarcz, 1996)--is critical to evaluation of the results. With the coeval rise of the Puuc centres, the potentially confounding effects of local deforestation and anthropogenic sedimentation on watertables and evaporation rates at Lake Chichancanab are also relevant to the isotopic trends. We would caution archaeologists to await more detailed presentation of these 188 Wright and White data and confirmation from other parts of the lowlands before embracing climate change as a trigger for the collapse. In conclusion, the Maya appear to have experienced a health burden that is not out of line with that of other complex preindustrial cultures. There is no evidence for consistent chronological change in either health stress indicators or diet and few data tie health stress directly to food consumption. Paleodietary reconstructions do not demonstrate a consistent trend of increasing environmental saturation and degradation but, rather, implicate both local environmental and political factors in the process of subsistence change. The implicit coupling of ecology with disease and nutrition in ecological models of the collapse is not upheld by the human biological data, which were so important to their genesis. Although appealing in simplicity, these models do not account for the local and regional variability revealed through more recent bioarchaeological investigations among the Maya. Indeed, the most dramatic change in human biology and health may have occurred during the Postclassic to Historic transition, as a consequence of the Spanish Conquest. Despite the recent upswing in bioarchaeology among the Maya, our understanding of ancient Maya diet and health is still spotty. At this time, we do not have data from enough sites with adequate chronological, spatial, and social representation to evaluate confidently the impact of diet and health patterns on the evolutionary success of prehistoric Maya peoples and their cultural institutions. We believe, however, that recent work is beginning to benefit from a more balanced view of the Classic Maya landscape and condition and that bioarchaeology will continue to enrich our perceptions of the ancient Maya past. ACKNOWLEDGMENTS In writing this paper, we have drawn on the work of many osteologists of the Maya and have attempted to give fair treatment to their work. Jane Buikstra first urged us to collaborate on a paper of this sort, and her encouragement is greatly appreciated. We thank the many archaeologists with whom we have worked for their insight and interest in the biological Maya past, and acknowledge their contribution to our own bioarchaeological work among the Maya through excavation, financial support, and encouragement. Pat Culbert and Mike Spence kindly read a draft of the manuscript and suggested several improvements, as did two anonymous reviewers. Our thanks also go to Eric Wright, who created Fig. 1. This paper was written while L. Wright held a Postdoctoral Fellowship from the Social Human Biology in the Classic Maya Collapse 189 Sciences and Humanities Research Council of Canada, support which is gladly acknowledged. REFERENCES Adams, R. E. W. (1983). Ancient land use and culture history in the Pasitn River region. In Vogt, E., Vogt and Leventhal, R. M. 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