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While evolutionary approaches to the human mind and behavior come in a variety
of forms (Heyes, 2003), evolutionary psychology represents a more restricted research
program that is focused on mental adaptations (Day & Wilson, 1999; Tooby & Cosmides,
1992). Adaptations are characterized by complex, functional organization that is
generally assumed to require many generations of persistent selection in order such
complex structures to emerge (Dawkins, 1986). As a result, this focus on adaptations
places a heavy historical constraint on evolutionary psychology. Evolutionary psychology
is restricted to the study of psychological mechanisms that would have been
advantageous in ancestral environments (Tooby & Cosmides, 1990). To the extent that a
trait is evolutionarily novel, evolutionary psychology would seem to have nothing
substantive to say about it. This limitation is further compounded by evolutionary
psychology’s emphasis on modular psychological mechanisms (Tooby & Cosmides,
1992), further restricting the scope of the hypothesized psychological adaptations.
Evolutionarily novel traits, per se, are not necessarily problematic for
evolutionary psychology. The approach naturally applies to only a restricted class of
phenomena and nonevolved traits clearly fall outside of its scope. However, when such
traits are complex and functionally organized, evolutionary psychology is seriously
challenged (Bloom, 1999). Evolutionary psychologists place considerable stock in the
claim that natural selection is the only scientifically plausible source of complex,
functional organization, yet abundant evidence speaks against this claim such as William
Paley’s famous example, the watch. Of course, Darwinists would want to make a
distinction between natural functional organization and artificial functional organization,
with the human eye being an example of the former and the watch being an example of
the latter. However, the heart of many debates around evolutionary psychology is
whether the human mind is better viewed as an artificial cultural construction. Although
theoretically beyond their purview, evolutionary psychologists had better have something
to say about evolutionarily novel functional organization. Gould (1991, 2002) has argued
that evolutionary psychology would benefit by adopting the concept of exaptation in
explaining aspects of human behavior and mental life that are evolutionarily novel.
However, the concept of an exaptation is, I will argue, ill-suited for explaining
evolutionarily novel functionality. Evolutionarily novel functionality suggests a different
sort of explanation in terms of co-opted adaptations that has been widely employed by
many evolutionary psychologists and associated researchers to account for a wide range
of evolutionarily novel traits. In this paper I attempt to systematize this disparate
literature to clarify the logic and scientific value of what I have called the modules and
metaphors program.
The Concept of Exaptation
In their classic paper on exaptations, Gould and Vrba (1982) begin their
discussion by noting that there are two conceptions of adaptation that were in use
amongst biologists. On the one hand there are biologists like Williams (1966) and
Darwin, himself, who restrict the term adaptation to traits that were “built by natural
selection for the function[s they] now serve,” on the other hand there are those biologists
such as Bock (1979) who more generally apply the term to any trait “that enhances
current fitness, regardless of its historical origin” (Gould & Vrba, both quotes p. 5).
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Gould and Vrba (1982) argue that this is a serious conflation of two largely unrelated
ideas: historical origin via natural selection and current utility. In an effort to correct this
confusion, Gould and Vrba coined the term, exaptation, to describe traits that currently
enhance fitness, but did not evolve for that reason.
We suggest that such characters, evolved for other usages (or for no function at
all), and later “coopted” for their current role, be called exaptations … They are
fit for their current role, and hence aptus, but they were not designed for it, and
are therefore not ad aptus, or pushed towards fitness. They owe their fitness to
features present for other reasons, and are therefore fit (aptus) by reason of (ex)
their form, or ex aptus [emphasis original] (p. 6).
Many evolutionary psychologists that I have discussed the concept of exaptation
with harbor the mistaken belief that exaptations are defined by their relation to some
structure. Typically it is assumed that the concept exaptation refers to coopted
adaptations or spandrels (the nonfunctional byproducts of adaptations, Gould &
Lewontin, 1979). Consider, for example, Buss, Haselton, Shackelford, Bleske and
Wakefield (1998) who suggest that there are two types of exaptations: co-opted
adaptations and co-opted spandrels, or Andrews, Gangestad, and Matthews (2002) who
define exaptations as “a pre-existing trait (i.e., one that has already evolved) that acquires
a new beneficial effect without being modified by selection for this effect” (p. 491,
emphasis mine). However, exaptations are not defined by their relation to any particular
structure, they are defined in the negative by the lack of a history of selection. Moreover,
even if one were to argue that exaptations necessarily bear a relation to some prior
structure, there is nothing in Gould and Vrba’s definition of the term that restricts their
relationship to prior evolved structures as these evolutionary psychologists do, i.e. there is
nothing ruling out exaptations as currently useful noise in the system (see, for example,
Gould, 2002, p. 1282-1284).
The Adaptivist and Adaptationist Programs
It is curious that such confusion should abound over the concept of exaptation,
because the critique that Gould and Vrba advance is one that evolutionary psychologists
strongly embrace. Prior to the late 1980’s the term evolutionary psychology was not in
general usage. In academia and the wider public at large, sociobiology was the term
generally applied to evolutionary analyses of the human mind and behavior. The term
evolutionary psychology was introduced to draw a distinction between two different
schools of evolutionary thought: the adaptivist program and the adaptationist program,
with evolutionary psychology the chosen label for the latter program as applied to the
study of the human mind. Given that much of what was previously called sociobiology
was research conducted within the adaptivist program, the new term, evolutionary
psychology, wasn’t simply a rebranding of sociobiology but the sign of a theoretical
fission within the human sociobiological community. It is difficult to understand
evolutionary psychology’s commitment to historical analysis and mental modularity
without an appreciation of the differences between these two research programs.
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In an influential string of papers, Symons (1987, 1989, 1990, 1992) drew a
distinction the adaptationist program as practiced by Darwinian psychologists (i.e.,
evolutionary psychologists) and the adaptivist program as practiced by Darwinian
anthropologists, owing primarily to the fact that many of the former are psychologists
(though not all, as Symons himself exemplifies) while many of the latter are
anthropologists. The adaptationist program is focused on identifying and explaining the
traits of organisms in terms of adaptation – components of an organism’s phenotype that
were specially designed by natural selection to solve an adaptive problem. An adaptive
problem is any long-standing problem that would have imposed significant selection
pressures in the evolutionary history of the species. It is the emphasis on special-design
as the mark of adaptation that has led to evolutionary psychology’s interest in mental
modularity. However, this does not imply any commitment to a Fodorian (1983)
definition of modularity, e.g., with an emphasis on informational encapsulation, but a
commitment first and foremost to psychological special-design.
Adaptivists also see their program as being focused on evolved traits, but the
adaptivist program is quite different from the adaptationist program. Rather than focusing
on the design of phenotypic traits, adaptivists focus on the reproductive consequences of
phenotypic traits, often in the context of the whole organism (Smith, Borgerhoff Mulder,
& Hill, 2000, 2001). The focus of research in this program is on traits that increase
reproductive success (or fitness proxies such as foraged calories), i.e. traits that are
adaptive. Adaptivists are generally less concerned about whether the trait in question
bears evidence of special design or has the right evolutionary pedigree.
It is in the context of this fission between adaptivist and adaptationist approaches
to human evolution that the term evolutionary psychology rose in prominence. The
critique, moreover, is not one-sided. Many Darwinian anthropologists have serious
misgivings with the research program advocated by evolutionary psychologists and prefer
instead to call themselves human behavioral ecologists (Smith et al. 2000, 2001). I
highlight this debate, not to weigh the relative merits of the two programs, but to draw
attention to the fact that evolutionary psychology is a very specific program of
evolutionary research (contrary to some inflationary claims, e.g. Heyes, 2003) which
leads to my more immediate concern, that adaptivists and adaptationists face different
theoretical challenges. Specifically, while the potential existence of exaptations poses a
serious risk to the adaptivist program, they should be of little or no concern to
adaptationists, i.e. evolutionary psychologists. “We believe that the failure of
evolutionists to codify such a concept [of exaptation] must record an inarticulated belief
in its relative insignificance” (Gould & Vrba, 1982, p. 13). I intend to do precisely this,
articulate the relative insignificance of exaptation to adaptationists.
Exaptations as an Adaptivist’s Problem
As a program focused on the reproductive consequences of contemporaneous
traits, the potential existence of exaptations poses an important challenge to the adaptivist
program (Barrett, Dunbar, & Lycett, 2002). The reason is straightforward, adaptivists
need be concerned that the traits that they are studying have the right sort of history to be
properly considered to have evolved. If Gould and Vrba’s (1982) analysis is correct, then
exaptations represent a class of traits that are not adaptations, but by virtue of their
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current utility are liable to be confused for such by adaptivists. Indeed, it is difficult not to
come to the conclusion that Gould and Vrba (see also Gould, 1991) primarily had
adaptivists in mind when promoting the concept of exaptation. Note, for example, their
discussion of Bock (1979) who explicitly defined adaptations in adaptivist terms: “An
adaptation is, thus, a feature of the organism, which interacts operationally with some
factor of its environment so that the individual survives and reproduces” (p. 39, quoted
from Gould & Vrba, 1982, p. 5). How adaptivists might deal with this problem will not
concern us here since we are primarily interested in the problems besetting evolutionary
psychologists.
Evolutionary psychologists qua adaptationists need not worry about the potential
existence of exaptations because the focus of their program is special design, not current
utility, and exaptations are not characterized by special design. Adaptationists face
difficulties of their own; they need to be vigilant against traits that are complex and
functionally organized, but are not plausibly adaptations, by virtue of the wrong historical
pedigree. It is these traits and not exaptations that could potentially be confused for
adaptations by evolutionary psychologists. Do such traits exist? Yes, I would contend, as
I have already alluded to above, that various cultural phenomena and many instances of
expertise arguably appear complex and functionally organized, yet lack the proper
history. Before considering such traits in detail, it will help to consider what role, if any,
the concept of exaptation might play in our understanding of them.
Unlike Symons’ unrelenting critiques of adaptivists, Gould and Vrba (1982) were
more pluralistic in their prescriptions. For while Symons has argued that adaptivism
represents a deep conceptual error of dubious scientific value (a “misuse of Darwinism”
to quote from one of Symons’, 1992, titles), Gould and Vrba largely accepted the
adaptivist program and simply recommended that it be recognized as the study of
aptation (environmental fit) rather than the study of adaptation: “we are not trying to
dismantle Bock’s [adaptivist] concept. We merely argue that it should be called aptation
(with adaptation and exaptation as its modes). As aptation, it retains all the favorable
properties for testing enumerated above” (p. 7). Indeed, Gould (1991) would later urge
evolutionary psychologists to consider exaptations as worthy of scientific study – “a
crucial tool for evolutionary psychology” to quote from the title of the paper. This is a
rather peculiar position for Gould to adopt given his earlier claim that “As evolutionists,
we are charged, almost by definition, to regard historical pathways as the essence of our
subject” (Gould & Vrba, 1982, p. 7) – a sentiment clearly shared by Symons and other
evolutionary psychologists. Clearly some theoretical exegesis is required here.
What is missing, both from Gould and Vrba’s (1982) discussion of exaptation and
Gould’s (1991, 2002) understanding of evolutionary psychology, is the theoretical
centrality of special design. It is precisely because adaptations are characterized by
complex, functional organization that adaptationists stress the importance of taking a
historical perspective – complex structures take a very long time to assemble via the
process of natural selection. Were adaptations simple in their organization – and
undoubtedly all evolved traits were initially simple in their structure – there would be no
need to posit a great depth of history. Special design is central to Williams’ (1966)
conceptualization of adaptation and it is central to Symons’ critiques of the adaptivist
program, but it is nowhere to be found in Gould’s (1991, 2002; Gould & Vrba, 1982)
discussion of exaptation or evolutionary psychology.
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According to the adaptationist program, evidence of special design and not
reproductive success plays a central role in the elucidation of evolved function. If some
phenotypic trait were shaped by natural selection for one function, but increased
reproductive success in contemporaneous environments by taking on a new role, it is the
past history of selection and not current reproductive success that would best account for
the detailed structure of the trait (Tooby & Cosmides, 1990). Indeed, unlike Gould and
Vrba (1982) who hold that one of the defining characteristics of adaptations is that they
currently useful: “a feature is an adaptation only if it was built by natural selection for the
function it now performs” (p. 5, emphasis mine), adaptationists do not take current utility
to be one of the defining characteristics of adaptations – the selective environment may
have changed rendering the trait useless, though possessing evidence of special design for
some past function all the same. Consider again, Paley’s watch. It makes little difference
whether the watch still functions or has ceased to do so, the complex design of the watch
demands an explanation – adaptations are no different. By focusing on design as opposed
to current utility, adaptationists are less likely to attribute the wrong selective history to
an exaptation than adaptivists. This focus on special design is just the corrective that
evolutionists need to avoid being misled by exaptations. That Gould and Vrba (1982) do
not mention this, let alone develop this theme, is astonishing given that they explicitly
acknowledge their debts to Williams (1966), in which this idea is thoroughly developed,
as an important precursor to their proposal.
Bait and Switch: Spandrels, Not Exaptations
Why should Gould and Vrba (1982) adopt the seemingly contradictory positions
of critiquing adaptivism on the one hand and embracing it as the study of aptation on the
other? Why should Gould and Vrba avoid all mention of special design? The answer to
both questions is clearly laid out in Gould (2002, see the section titled “The complete
version, replete with spandrels: Exaptation and the terminology of nonadaptive origin” p.
1246 ff.): the concept of exaptation was introduced to bolster the import of another of
Gould’s theoretical developments, the concept of a spandrel (Gould & Lewontin, 1979).
“The key to this expansion of evolutionary theory [to include traits that never were
adaptations] therefore lies in the category of currently useful traits with nonadaptive
origins” (Gould, 2002, p. 1248). Without a science of aptation, there would be no need
for the systematic study of traits with nonadaptive origins and an appreciation of the
significance of special design would compromise the whole project.
Reading Gould (1991, 2002) more carefully, it is clear that his main
recommendation to evolutionary psychologists is not that they should employ the concept
of exaptation more often, but that they should consider the possibility that important
constituents of the mind have their origins as spandrels, not as adaptations.
A failure to appreciate the central role of spandrels, and the general importance of
nonadaptation in the origin of evolutionary novelties, has often operated as the
principal impediment in efforts to construct a proper evolutionary theory for the
biological basis of universal traits in Homo sapiens – or what our vernacular calls
“human nature.” (Gould, 2002, p. 1264).
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Why spandrels?
Natural selection built the brain; yet, by virtue of structural complexities so
engendered, the same brain can perform a plethora of tasks that may later become
central to culture, but that are spandrels rather than targets of the original natural
selection (Gould, 1991, p. 57).
Simply put, by virtue of the human mind’s complexity, the number of spandrels must
vastly exceed the number of adaptations, hence by sheer numerical superiority, spandrels
will play a far greater role as co-optable structures than adaptations. There are problems
with this argument, but before considering them, it is necessary to clarify that spandrels
are neither identical to exaptations nor did Gould prioritize the study of exaptations over
the study of spandrels.
Exaptations, as we have seen above, can either trace their origins either to prior
adaptations or to nonadaptive structures such as spandrels and noise in the system.
Hence, the set of spandrels is not coextensive with the set of exaptations. Moreover, it is
clear from the emphasis that Gould (1991, 2002) places on co-opted spandrels as opposed
to co-opted adaptations – of which he gives no human examples nor devotes much
discussion – that he is less concerned with the possibility of exaptation, per se, than he is
with the possibility that a major portion of the human mind may be nonadpative in origin.
This is reinforced by the fact that Gould devotes no discussion to one of the key features
of exaptations; namely, that they are currently useful. Although Gould (1991) mentions
several possible exaptations, in no instance does he provide any evidence that they are
currently useful in either the biologist’s sense of enhancing reproductive success or
according to any other metric, though perhaps he felt that the utility of traits such as
“singing Wagner” is self-evident.
The failure to specify the manner in which cultural traits such as “reading,
writing, or any form of mental expression not in the initial repertoire of large-brained
populations; add most of the fine and practical arts, the norms of commerce, the practices
of war” (Gould, 1991, p. 59) are currently useful is no small oversight. There is a long
tradition of anthropological functionalism that claims precisely this (Malinowski, 1922;
Radcliffe-Brown, 1952). Gould (1991, 2002) makes no reference to this extensive
literature because, as a biologist, he is presumably advocating a specific conception of
utility in terms of reproductive success as suggested by Gould and Vrba (1982).
Anthropological functionalism wasn’t without its critics and biological functionalism of
the sort that Gould would appear to be advocating would face even fiercer resistance. All
of this leads to the conclusion that Gould was not advocating wider use of the concept
exaptation, but wider consideration to the possibility that contemporary human traits may
have nonadaptive origins.
This brings us back to the argument that spandrels, by their sheer numerical
superiority as co-optable structures, will be far more important to the study of the human
mind than are adaptations. There are two problems with this argument. First, it assumes
that evolutionarily novel traits will be more important, not just to the study of human
mind and behavior in general, but even to human nature (see quote above). Second, it
assumes that existence is the sole criterion for co-optability, ignoring other relevant
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properties such as a trait’s potential to do useful work. Gould (1991, p. 59) is cognizant
of the former problem and addresses it forthrightly:
Go down the list of what you regard as human universals and cultural
predictabilities. How many would you putatively assign to adaptation, and
therefore view as amenable to sociobiological explanation? Incest avoidance?
Such universal gestures as eyebrow flashing? Fine – but how long is your list and
how much of our human essence, how much of what really makes culture, will
you find?
Unfortunately, the matter is more complicated. Consider, for example, language.
Reading and writing, two of Gould’s putative exaptations, are undoubtedly evolutionarily
novel, but not entirely. They are built on a cognitive adaptation for spoken language
(Pinker, 1994; though Gould, 1991, p. 61-62, argues that spoken language is likewise an
exaptation). Consider another of Gould’s (1991) examples, arithmetic. Undeniably,
formal arithmetic is an evolutionarily novel cultural construction, but there is very good
evidence suggesting that formal arithmetic is an elaboration of two evolved number
systems (Dehaene, 1997): one for exact, small number calculations (Wynn, 1995) and
another for approximate large number calculations (Dehaene & Cohen, 1991). Religion,
another of Gould’s (1991) putative co-opted spandrels has also been analyzed in terms of
co-opted adaptations (Boyer, 2003).
Moreover, Gould’s (1991) own list of co-opted spandrels: reading and writing, the
norms of commerce, and the practices of war, casts doubt upon his argument because
these are not human universals. Numerous cultures exist or have existed within the past
millennia that lacked a written language (Pinker, 1994). The norms of commerce are not
universal, but vary within a restricted repertoire (Fiske, 1991). Likewise, it would be
difficult to maintain that the practices of war are universal cross-culturally. What is
universal are universal grammar, trade and warfare, more generally (Brown, 1991), but at
this level of generality, adaptationist claims are quite plausible (Pinker, 1994; Cosmides
& Tooby, 1992; Wrangham & Peterson, 1997, respectively).
Looking beyond this possibly ill-chosen list of examples, it surely is the case that
spandrels vastly outnumber adaptations. Moreover, as I will argue later, it is not human
universals that challenge evolutionary psychology, but some cross-cultural differences
and there are stronger grounds for believing that cross-cultural differences map onto
evolutionarily novel traits than do cross-culturally universal traits. So the question
remains, do spandrels provide a better source of co-opted traits than do adaptations,
raising the important question of the relative co-optability of spandrels and adaptations.
Gould (1991) initially had little to say about the co-optability of spandrels, but in
The Structure of Evolutionary Theory (Gould, 2002, p. 1277 ff.), the issue of the relative
co-optability of traits is addressed more substantially, where he draws a distinction
between inherent potentials and available things for co-optation. Inherent potentials are
potential, but nonmanifested uses of a trait.
The inherent potentials of any object (for uses other than their intended purpose of
manufacture) establish a large and important category of attributes in the exaptive
pool of any individual (Gould, 2002, p. 1278).
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Available things are simply that, traits that are potentially available to be co-opted.
The attributes in the second major category of the exaptive pool are, by important
contrast, actual entities, pieces of stuff, material things that have become parts of
biological individuals for a variety of reasons…, but that have no current use
(Gould, 2002, p. 1279).
Gould further treats these as not only as mutually exclusive “attributes,” but also
seemingly as mutually exhaustive attributes. Presumably, one would imagine that the
probability that a class of traits: adaptations, spandrels, or noise, would be co-opted
would be a simple function of their frequency as available things weighted by the
strength of their inherent potential – i.e., that these are different aspects of a trait. Yet,
Gould only treats traits with no current use as being available things, thereby excluding
adaptations that are presently useful and exaptations, which are by definition currently
useful. What then are adaptations and exaptations, which Gould and Vrba (1982)
collectively refer to as aptations or traits that fit their environment? Presumably they are
inherent potentials: Inherent potentials “capture the important concept so poorly
expressed in the old term ‘preadaptation’ – that is, suitability for anther function not
presently exploited because the feature has been adapted by natural selection for a
different utility” (Gould, 2002, p. 1278, emphasis mine). Moreover, one is forced to
assume that inherent potentials are things, just like available things, in order to avoid
attributing a series of categorical errors to Gould (2002, p. 1285) when he proposes the
combination inherent potentials with various subcategories of available things. Hence,
rather than contrasting traits with adaptive origins with traits with nonadaptive origins
(Gould, 1991), Gould (2002) contrasts currently adaptive traits with currently
nonadaptive traits.
Unfortunately, Gould (2002) again digresses into an argument for the greater
frequency of spandrels as available things, this time at the species level, as opposed to the
organismal level as spandrels were originally conceived (Gould & Lewontin, 1979). Yet,
his choice of terminology and expressed intention are quite informative. The restriction
of the term inherent potentials to traits that that are presently useful would appear to
concede that use begets use. Second, Gould (2002, p. 1286, Gould regularly uses the
arcane terms Franklins and Miltons interchangeably with inherent potentials and
available things, respectively. I substitute the latter for the former here) clearly abandons
the effort to present a convincing argument that nonadaptive traits are more co-optable
than adaptive traits: “I chose this [basis of primary ordering] because [available things]
(and not [inherent potentials] pose a genuine challenge to the exclusivity of adaptationist
mechanisms.” Indeed, in the discussion that follows, Gould draws out the radical nature
of his proposal without ever justifying an emphasis on nonadpative traits in terms of their
contribution to the phenotype of an organism. In the end, no convincing argument is ever
offered for expecting traits with nonadaptive origins will make the largest contribution to
the functional organization of an organism other than the fact that spandrels possess a
numerical advantage.
Novel Design as an Adaptationist’s Problem.
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The foregoing discussion should not leave one with the impression that
evolutionarily novel traits pose no problems for adaptationists, because they can indeed,
be quite problematic (Bloom, 1999). However, the challenge to the adaptationist program
is not posed by exaptations or spandrels, but by instances of evolutionarily novel
functional1 organization. The reason is straightforward. Complex functional organization,
i.e., special design, is assumed by adaptationists to be diagnostic of adaptations, so if
evolutionarily novel functionality exists, it drives a wedge between special design and
historical origin – i.e., one can no longer assume that traits bearing evidence of special
design have evolutionary origins in the process of natural selection. Exaptations pose no
special challenge in this respect because they are not characterized by the evidence of
special design in the way that adaptations are. Exaptated adaptations, can be quite
problematic in this respect, though this is not by virtue of their continuing to enhance
reproductive fitness, but by virtue of their co-opting a prior design for a novel function.
Hence, co-opted, but nonexaptated, adaptations are equally problematic. Ultimately, coopted adaptations or exadaptations, as I will call them, do not pose an insurmountable
problem to evolutionary psychologists. Indeed, the possibility that adaptations can be coopted for novel purposes potentially extends the scope of evolutionary psychology to
include some evolutionarily novel traits. It is the study of precisely these traits that is the
focus of what I will call the modules and metaphors program, but before considering this
program in detail it will be necessary to consider the more problematic cases of
evolutionarily novel functionality with nonadaptive origins.
Evolutionarily Novel Functionality with Nonadaptive Origins
Gould (1991, 2002), of course, has argued that former spandrels represent an
important class of exapted traits. Do co-opted spandrels display evolutionarily novel
functionality? Regardless of whether they are exapted or simply co-opted, it seems rather
unlikely that spandrels could be confused for adaptations since, almost by definition,
spandrels are parts and not functional wholes. Hence, spandrels, as Gould’s (2002)
classification as available things and not inherent potentials suggests, are less likely to
have potential functionality. Any particular spandrels may, of course, play a functional
role in some novel structure or function, but in isolation, a spandrel is not likely to be
confused for an adaptation proper as opposed to an adaptive design feature – an important
component part – of a candidate adaptation. Over evolutionary time, a former spandrel
may come to occupy a larger and larger functional role, but at this point we would no
longer be considering an evolutionarily novel trait. Similar arguments and more
convincingly apply to instances of co-opted system noise.
Far more problematic than co-opted spandrels and noise are instances of
expertise. Although discussions of evolutionarily novel functionality often revolve
around cultural traits, cultural traits tend to be a manifestation of a more general problem,
expertise – i.e., acquired competence. Expertise is problematic because mental
mechanisms underlying it bear evidence of some of the same qualities invoked as
evidence of “special-design” in psychological adaptations. Not only is expertise domainspecific, but experts “have their knowledge organized in particular ways, ways that make
that knowledge more accessible, functional, and efficient” (Bédard & Chi, 1992), some of
10
the very same attributes that have been attributed to psychological adaptations (Tooby &
Cosmides, 1992).
Typically, however, expertise is viewed as an individual trait. Most of us are
novices at specific skills, arts and sciences, with a much more restricted range of
individuals displaying markedly better ability being deemed experts. Indeed, the word
would seem to loose its meaning if everyone were an expert at a particular task. The
individual nature of expertise is in marked contrast to the species-universal expression of
adaptations suggested by evolutionary psychologists (Tooby & Cosmides, 1992). Hence,
it would seem unlikely that expert abilities would ever be confused with adaptations.
Moreover, Bloom (1999) has questioned the significance of acquired expertise by arguing
that no one person acquires expertise on his own, but relies on a history of cultural
evolution to accumulate the knowledge that individual experts then acquire. This,
however, would seem to miss the point. To the extent that experts exhibit complexly
organized functionality in their domain of expertise (and arguably they do), then natural
selection would not appear to be a privileged source of functional design. Moreover,
there is no reason why expertise should only be considered an individual trait. Wagner
(1999) has argued that reading could be considered a form of expertise displayed by most
Western adults – one could, for example, compare early learners with adults who have
achieved full reading competence. Indeed, it could be argued that we all are experts to
some extent when it comes to the practices of our culture(s). Those who participate fully
in a religion are experts at that religion. Hence, there is not such a clear separation
between cultural practices and individual expertise.
Cultural and individual expertise, however, are just symptoms of a far more
vexing problem. While cultural and individual expertise suggest alternate sources of
functional design, their manifestations are not readily confused for natural design due to
fairly clear signs of recent origin and their heterogeneous distribution through human
populations. However, a potential alternate source of functional design opens the door to
the possibility that even universal traits are examples of expertise and not adaptation.
Consider two hotly debated examples, face processing and cheater detection. A number
of researchers have argued that face processing constitutes an innate, domain-specific
competence (see Kanwisher, 2000) that some evolutionary psychologists have argued is
an evolved adaptation (Duchaine, Cosmides, & Tooby, 2001). Opposing this view are
those who argue that face processing is a form of acquired expertise (e.g., Diamond &
Carey, 1986; Gauthier & Tarr, 1997). Or consider the debate over social reasoning on the
Wason selection task. Cosmides and Tooby (1992; Cosmides, 1985, 1989) have argued
that “cheater detection” on social contract versions of the selection task is the product of
evolved, cognitive adaptations for social exchange. One of the most favored alternative
explanations is pragmatic reasoning schemas theory (Cheng & Holyoak, 1985), which
argues that humans typically acquire domain-specific knowledge structures relating to
social regulations by virtue of extensive, goal-directed exposure to such rules – in effect,
that humans typically acquire an expertise for reasoning about social regulations such as
social contracts. Acquired expertise represents a serious challenge to the adaptationist
program for it not only represents an alternative account of functional design, but also, as
these purported examples illustrate, expertise need not be limited to culturally and
individually variable competences, but may extend to universally expressed competences.
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Of course, the challenge raised by expertise and other forms of evolutionarily
novel functionality is that they arise de novo – that the structure of the underlying
mechanisms is, to some interesting extent, not co-opted from prior adaptations. It is far
from obvious that this is indeed the case. In casting doubt on this claim I do not simply
mean the trivial objection that learning requires a learning mechanism that in turn may be
an adaptation. No, I mean that it is far from clear that the structure of the compiled
mechanism itself is novel as opposed to borrowed from a pre-existing adaptation.
Expertise may also depend on the co-optation of adaptations to some interesting extent.
The Modules and Metaphors Program
A wide variety of researchers including cognitive anthropologists, cognitive
neuroscientists, and evolutionary psychologists have conducted research on
evolutionarily novel competences according to a common set of assumptions or goals: 1)
natural selection has shaped the human mind to provide it with a range of cognitive
adaptations for solving problems that would have confronted ancestral humans, 2)
evidence for these adaptations comes in the form of universal, domain-specific
psychological faculties or knowledge, i.e. modules, 3) these mental adaptations have been
co-opted or culturally elaborated giving rise to evolutionarily novel phenomena such as
law, literature, mathematics, science and religion, and 4) research in this program strives
to understand the structure of cultural phenomena in terms of mental structure inherited
from prior psychological adaptations and not the current utility of cultural phenomena.
Hence, the focus of this research program is on exadaptations, not exaptations. Perhaps
the most articulate exponent for this emerging research program is Dan Sperber (1994;
Sperber & Hirschfeld, 2004) who has initiated some of the themes that I will elaborate
upon here.
Modules
The term module means different things to different people. Perhaps the best
known characterization of modules is Fodor’s (1983) analysis of input systems – i.e.,
perceptual systems and language. Fodor proposed that modules possess a collection of
properties such as domain-specificity, informational encapsulation, limited central access,
and a fixed neural architecture. Evolutionary psychologists, on the other hand, have
viewed cognitive adaptations more generally as modules, be they input systems or central
processes (Cosmides & Tooby, 1994). According to this analysis, modules qua cognitive
adaptations bear evidence of special design for solving specific adaptive problems
(Tooby & Cosmides, 1992). Cognitive adaptations will, of course, tend to possess many
of the properties identified by Fodor such as domain-specificity, speed, a fixed neural
architecture and a robust and reliable development, but there is no reason to assume that
they will necessarily possess these or any other of Fodor’s proposed properties. To begin
with, Fodor restricted his analysis to input systems and it would be rather arbitrary to
restrict mental adaptation in this way. Properties such as limited central access, shallow
outputs (at least so far as this means nonconceptual representations), and mandatory
operation (at least with respect to externally presented input stimuli) that primarily apply
to peripheral mechanisms are, therefore, overly restrictive. More importantly though,
12
there is no reason to assume that modules constitute a classical category with necessary
and sufficient features. Like many other biological kinds, modules will presumably
display a family resemblance relation to one another with no one set of features shared
between all members, but each module bearing some subset of features characterizing the
kind more generally. Special design also evades strict definition in terms of necessary and
sufficient properties (Williams, 1966). Instead, one will have to proceed on a case by case
basis using a task analysis of the problem to be solved to see if there is sufficient
justification for concluding that a specific mechanism is an adaptation. Because different
adaptive problems pose different challenges, it is unlikely that there will be any universal
standard of special design. As with the concept of fitness, the “specialness” of any one
design can only be judged with respect to alternative designs. Likewise, the domainspecificity, informational encapsulation, speed, and so forth of any one mechanism can
only be judged with respect to alternative mechanisms.
One can think of adaptations as having an organized structure that embodies a
particular mode of operation, a modus operandi, that was designed for a specific set of
problems encountered in ancestral environments. Keil (1994) has referred to a cognitive
mechanism’s mode of construal, however, this frames things not only in cognitive terms
but in a relatively narrow way suggesting that the task of a cognitive mechanism is
conceptualization. Not only does this choice of terminology fail to capture different types
of information processing such as inference, but it would also be awkward to apply to
noncognitive adaptations such as the heart. Hence, I will refer more generally to an
adaptation’s modus operandi. The modus operandi is not the same as an adaptation’s
function, where function is the adaptive effect that the adaptation brings about. The
difference is that between means and ends. The modus operandi of an adaptation is the
means by which it brings about its adaptive ends or functions. Given the multiple
realizability of functions (Fodor, 1975, 1981; Putnam, 1975), the modus operandi of an
adaptation more closely reflects its particular structure than does the adaptation’s
function. While Fodor’s and Putnam’s analyses of function were focused on cognitive
functions, not biological functions, the same arguments would readily apply to biological
functions as suggested by biological analogues like the wings of birds, bats and insects.
Perhaps less problematically one can borrow the term, domain, from the cognitive
sciences to refer to an adaptation’s range of application – that which the adaptation acts
upon. A domain is not necessarily a body of knowledge or information, but can be
viewed more broadly as the object, substance, or entity upon which the adaptation acts,
which may or may not contain an informational component. Again, consider the heart.
One can think of blood as the heart’s domain of application – the substance upon which it
acts – without thereby committing oneself to a conception of a domain in terms of
informational content. Typically the domain of an adaptation is in some sense external to
it and, in many cases, even external to the organism. The blood that the heart pumps is
not intrinsically part of the heart, but external to it – part of its environment. Therefore,
one can make a distinction between the complex, functional structure of an adaptation,
most clearly reflected by its modus operandi, and its domain of application, that aspect of
the environment that it operates on, to bring about an adaptive end, the adaptation’s
function.
An important distinction for the modules and metaphors program is that between
an adaptation’s proper and actual functions (Millikan, 1984; Sperber & Hirschfeld,
13
2004). The proper function of an adaptation is the set of its effects that are causally
responsible for the adaptation’s existence and design – i.e., what biologists typically refer
to as an adaptation’s function. The actual function of an adaptation is the set of effects
that it currently brings about, regardless of whether these contributed to the existence and
design of the adaptation. Millikan (1984, p.2) illustrates the distinction with the following
example. The human hand undoubtedly evolved for “grasping, manipulating, pushing or
pulling.” These are proper functions of the hand. Yet, hands can also be used “as matter
upon which to draw, as subjects for physiological experimentation, as objects of aesthetic
contemplation, etc.” These uses, in addition to grasping, manipulation, pushing and
pulling, are actual functions of the hand. Sperber (1994) later extended this idea in
drawing a distinction between an adaptation’s proper and actual domains, where the
proper domain of an adaptation is that which it was selected to operate on whereas the
actual domain is that which it does operate on regardless of whether it was selected to do
so. These distinctions between proper and actual functions / domains are adaptationist
distinctions. It is the past history of selection that determines which effects are and are
not part of an adaptation’s proper function. An adaptivist, on the other hand, might follow
Gould (2002) and distinguish between effects that do and do not currently enhance fitness
(inherent potentials and available things, respectively), but given that these are defined in
terms of present as opposed to past utilities, these would not be coextensive with the
proper and actual functions of an adaptation. Likewise, exaptations, or more properly
their effects, do not coincide with the actual functions of an adaptation for not only may
the actual function of an adaptation include its proper functions, the actual function of a
mechanism is not limited to those effects that enhance fitness. More importantly though,
it is the adaptationist’s focus on organized structure and the recognition that such
structures can persist, lag behind environmental changes, that recommends an
adaptationist, but not an adaptivist, account of metaphor.
Metaphors
Metaphorical and analogical reasoning processes in humans have been widely
documented by cognitive linguists (e.g., Lakoff, 1987) and cognitive psychologists (e.g.,
Gentner, Holyoak, & Kokinov, 2001). Metaphorical thought processes entail mapping the
structure of a source domain onto a target domain. There are, however, constraints on
this mapping. First, as Lakoff (1987, p. 276) notes, “To function as a source domain for a
metaphor, a domain must be understood independent of the metaphor.” Hence, in order to
serve as a source domain, one must already have an intuitive understanding of the
domain, which is exactly what cognitive adaptations provide for their proper domain of
application. Moreover, cognitive adaptations provide a structured understanding of their
proper domains and it is this structure or modus operandi that can potentially be applied
to the target domain.
A second constraint on metaphorical thought processes rarely if ever discussed by
students of metaphor is the need to contain informational corruption (Cosmides & Tooby,
2000). Consider one of Lakoff’s (1987) metaphors, anger (target domain) as a heated
fluid in a container (source domain), as in “He was bursting with anger” (p. 385,
emphasis original). Whatever practical use this metaphor has could easily be outweighed
by the potential damage done to one’s stored knowledge were one to erroneously store
14
the belief that anger is in fact a heated fluid in a container. Were this to happen one
might entertain the erroneous beliefs that one could cook with anger, heat a home with it
or drive a piston with it. Alternatively, one might attempt to reduce someone’s anger by
pouring cold water on them. What prevents this from happening when concepts from
these two domains are brought together and connected in thought?
Cognitive linguists have implicitly recognized the significance of this problem by
embracing Fauconnier’s (1994, 1997) theory of mental spaces, which effectively deals
with it. Mental spaces are cognitive workspaces within which the contents of discourse or
thought can be represented. Without delving too deeply into Fauconnier’s theory, several
aspects of mental spaces are worth noting. First, multiple mental spaces can be
entertained simultaneously, but new spaces are always introduced within a parent space,
the original parent space being the speaker’s or thinker’s understanding of reality. In the
embedded spaces, truth relations can be suspended or made conditional on the space. For
example, suppose someone was considering a picture that Alan took of Mary. The person
might construct a picture that Alan took space in which Mary might be wearing a red
dress, whereas in reality as the thinker knows it (the parent space) Mary is wearing pants
and a white blouse. Second, although connections may be made between spaces – the
Mary in the picture that Alan took space is connected to the Mary in the parent reality
space – the contents of an embedded space cannot migrate to the parent space, i.e.,
Mary’s wearing a red dress is contained within the picture that Alan took space.
Moreover, logical relations only hold within a space – i.e., within the picture that Alan
took space, Mary cannot simultaneously be wearing a red dress and not wearing a red
dress, whereas between spaces logical contradictions such as this may hold. Therefore,
the contents of an embedded space cannot alter the contents of the parent space though
their logical entailments, i.e., the fact that Mary is wearing a red dress in the picture space
does not cause one to revise one’s belief that Mary is wearing pants and a blouse in the
parent reality space. Thirdly, many cognitive linguists, including Fauconnier (1997), have
analyzed metaphor as a mapping from a parent source-domain space to an embedded
target-domain space. Hence, given the bounded and contained nature of mental spaces,
metaphorical thoughts entertained within the embedded target-domain space cannot
migrate to the parent space (the thinker’s reality space), thereby corrupting his or her
knowledge of the world.
Although Fauconnier and others have put mental space theory to considerable use
in explaining many aspects of language and discourse, no cognitive linguists that I am
aware of has offered an account of why humans possess the ability to form mental spaces.
Cosmides and Tooby (2000), on the other hand, have provided an evolutionary
explanation of why such mechanisms are needed to avoid informational corruption.
Rather than adopting Fauconnier’s mental space framework, they suggest that a system of
metarepresentations in which truth relations are suspended are required to handle the
problems of informational corruption posed by communication and various forms of
thought. Fauconnier’s mental spaces are simply a specific instance of such a
representational system and so I will refer more generally to the ability to form
metarepresentations.
Both Fauconnier (1994, 1997) and Cosmides and Tooby (2000) consider these
metarepresentational abilities to be a separate faculty of mind. This raises the possibility
that metaphorical thought may be dissociable from other thought processes. Evidence
15
from autism suggests precisely this. It has been suggested that autism is characterized by
an impaired ability to form metarepresentations (Suddendorf, 1999). It is interesting to
note, therefore, that persons with autism appear to have a reduced appreciation of
metaphor. They also have difficulty imagining the unreal (Scott & Baron-Cohen, 1996).
Mention Gilbert experiment and Hermer and Spelke experiments here
from an adaptationist perspective, such intuitive understanding is structured –
embodies a particular modus operandi. An adaptationist account of metaphor
However, Boyer (1994) has objected to the nonrigorous use of “metaphor” as a
mechanism for understanding religious thought, but trope of metaphor is a familiar one
that gives a good sense of the phenomenon I am proposing and, nonetheless, is harmless
provided one spells out the mechanism by which metaphorical inferences are achieved.
One of the ways in which the concept of “metaphor” is made more rigorous within this
program is by supplying a scientifically sound theory of base domains. One of the
problems besetting the study of metaphor in cognitive linguistics (e.g., Lakoff, 1987), for
example, is the lack of a coherent theory of base domains. Thought, according to Lakoff
(1987) is both embodied and imaginative. Metaphor, an important aspect of imaginative
thought, employs concepts derived from our embodied cognition. But what is embodied
cognition?
Thought is embodied, that is, the structures used to put together our conceptual
systems grow out of bodily experience and make sense in terms of it; moreover,
the core of our conceptual systems is directly grounded in perception, bodily
movement, and experience of physical and social character (p. xiv, emphasis
original).
However, a definition of embodied cognition such as this either includes too much or too
little. Assuming that we are materialists and not dualists, what is excluded from this
definition? If nothing is excluded, then how can we make sense of Lakoff’s
characterization of imaginative thought?
Thought is imaginative, in that those concepts which are not directly grounded in
experience employ metaphor, metonomy, and mental imagery – all of which go
beyond the literal mirroring, or representation, of external reality. It is this
imaginative capacity that allows for “abstract” thought and takes the mind beyond
what we can see and feel. The imaginative capacity is also embodied – indirectly
– since the metaphors, metonymies, and images are based on experience, often
bodily experience (p. xiv, emphasis original).
Clearly, Lakoff has a restricted sense of embodiment in mind, otherwise there would be
no room left for imaginative thought. But if the base domains are restricted to concrete,
physical existence, then how can we begin to make sense of the mind-body problem, not
16
its solution, but the very fact that it is or ever was viewed as a problem? For if mind, a
nonphysical concept, is based on physical metaphors, how could it ever appear that the
former is incompatible with the latter?
The modules and metaphors program handles problems such as these with ease.
Our evolved human nature supplies our base domain concepts and inferences.
Evolutionary theory provides clear guidelines as to what these base domains might be,
they are constituted by the adaptive problems that would have confronted our ancestors.
Evolutionarily novel problems constitute the range of target domains to which our
repertoire of evolved concepts and inferential machinery can be imaginatively applied.
Problems of translation, from mind to body, and the like, result from the modularity of
the cognitive adaptations. Concepts designed for one adaptive problem may be
unavailable to or incommensurate with other adaptive problems. Moreover, the
metaphorical extensions of base concepts could potentially inherit these same properties,
with concepts derived from one adaptive problem being incommensurate with those
derived from different adaptive problem. This line of analysis could, in turn, also be
extended to account for incommensurate, cultural worldviews.
It should be noted that an evolutionary account of cognition need not preclude the
possibility that cognition is embodied. On the contrary, the sort of framework typically
adopted by evolutionary psychologists (e.g., Tooby & Cosmides, 1992) represents a
specific theory of how cognition is embodied. Consider, for example, the following
descriptions of embodiment offered by Lakoff (1987):
Conceptual embodiment: The idea that the properties of certain categories are a
consequence of the nature of human biological capacities and of the experience of
functioning in a physical and social environment. It is contrasted with the idea
that concepts exist independent of the bodily nature of any thinking beings and
independent of their experience.
Functional embodiment: The idea that certain concepts are not merely understood
intellectually; rather, they are used automatically, unconsciously, and without
noticeable effort as part of normal functioning (pp. 12-13).
This view of cognition as pragmatic and shaped by the life-history of the organism is
quite similar to that espoused by evolutionary psychologists. Moreover, the automatic,
unconscious, and effortless quality of embodied cognition fits squarely with the view that
cognitive adaptations are modular instincts (cf. Fodor, 1983). Where the evolutionary
view diverges from Lakoff’s account of embodiment is in the mechanism by which
embodiment is achieved. Lakoff’s mechanism of embodiment is question-begging given
that it relies upon unmediated experience as the source of cognitive structure, but
experience, in the psychological sense, requires a prior set of cognitive mechanisms that
do the experiencing. Experience in a direct physical sense leaves unexplained how the
mind is shaped by the physical environment. By contrast, the theory of evolution by
natural selection provides a workable mechanism by which the mind can be shaped to fit
the physical environment.
How does the program work?
17
Is it compatible with evolutionary psychology?
Is it compatible with evolutionary psychology?
In The Prehistory of the Mind, Mithen (1996) launched into an attack on
evolutionary psychology citing precisely the sort of phenomena that I have suggested the
modules and metaphors program can handle – cultural innovations of anatomically
modern humans in which evolved, purportedly modular abilities are applied outside of
their proper domains. According to Mithen this dissolution of domains constitutes prima
facie evidence that the mind of modern humans is not modular. This argument has been
further taken up by Chiappe (2000) who argues that cross-domain integration is
particularly evident in the phenomenon of metaphor, a key element of my proposed
program for dealing with evolutionarily novel, cultural phenomena and expertise. Hence,
the question inevitably arises is what I am proposing complementary to or opposed to
evolutionary psychology? Yes, I would argue, the modules and metaphors program is
compatible with evolutionary psychology. It requires evolutionary psychology as a means
of investigating source conceptual and inferential domains. What these critiques turn on
is an overly narrow view of modules, one that evolutionary psychologists need not and do
not subscribe to.
Ultimately, the appeal of modularity to evolutionary psychologists is that it
appears to capture the adaptationist’s concept of “special design.” Special design
typically viewed in engineering terms of economy, efficiency, accuracy, and so forth,
with the claim being made that domain-specific mechanisms are more likely to exhibit
these qualities than domain-general mechanisms (Tooby & Cosmides, 1992). To the
extent that a domain-general mechanism is more economical, efficient, and accurate than
a domain-specific mechanism, then natural selection should clearly favor the domaingeneral mechanism. That a mechanism is informationally encapsulated, cognitively
impenetrable, mandatory, fast or possess any other quality characteristic of modules
according to Fodor (1983) is irrelevant – though the argument could easily be made, for
example, that to the extent that cognitive adaptations are economical and efficient they
will be informationally encapsulated and fast.
These qualities of special design, economy, efficiency, accuracy, and so forth are
not simply abstract concepts, they refer to biological structures. The qualities of special
design act as a guide in determining the function of the structure under investigation as a
means of explaining the organization of that structure. Again, special design and its
associated qualities are relative to a particular set of environments – the ancestral
environments in which the mechanism evolved. There is no incoherence in claiming that
adaptive design lags behind environmental changes – evolution thorough natural
selection is an extremely slow process. Consequently, it is not problematic for
evolutionary psychologists when an evolved structure persists and even operates in novel
environments that it was not designed for.
Once we distinguish between the structure of a mechanism (embodying a
particular modus operandi) and its domain of application, we have all we need to answer
the critics. The complex, functional structure of an evolved mechanism can persist and
continue to operate despite radical changes in the environment in which it operates.
While its proper domain of application remains fixed, its actual domain of application can
18
change with changing environmental circumstances. What is problematic for an
evolutionary view of mind, regardless of whether the mechanisms in question are
domain-specific or domain-general – is not sudden changes in the domain of application
but sudden changes in the organizational structure of the mechanism. What the critics
need to argue, but have not, is that complex functional design of a cognitive adaptation is
changed in the near term (and not simply towards dysfunction) by changes in the
environment. Yet this is not what Chiappe (2000), for example, claims. Indeed, the very
phenomenon that Chiappe invokes against the modularity of mind, namely metaphorical
reasoning, assumes a persistence of structure. Were the structure of an organizing concept
from a base domain to change in the process of being applied to the target domain, the
end result would fail to be a metaphor.
Exadaptations
How does that work?
Do they exist?
There are, perhaps other types of byproducts, such as vestigial organs, but the
type of byproduct that I have in mind when coining the term exadaptations are
adaptations that have largely been co-opted for evolutionarily novel uses (Buss, Haselton,
Shackelford, Bleske, & Wakefield, 1998, refer to these as co-opted adaptations). When
speaking of psychological adaptations, it will help to make a distinction between an
adaptation’s modus operandi and its domain of application. When the environment
changes from ancestral conditions, there can be a lag in which the adaptation continues to
operate, but is applied in different circumstances. With morphological adaptations, the
persistence of the adaptation in the face of changing environmental circumstances is easy
to detect – the physical structure either remains or it does not. Take a fish out of water
and its fins remain. They look pretty much as they did in water and probably move much
the same way as well. With psychological adaptations the picture is less clear, it is much
more difficult to point to a physical structure. Instead, psychological adaptations are
potentially recognized by their modus operandi, their characteristic way of operating –
even with quite radical changes in the domain of application, operation of a psychological
adaptation can potentially be detected if its modus operandi is sufficiently distinctive.
There are a variety of ways in which the domain of application of a cognitive
adaptation can be altered. The environment can change such that the adaptation’s
proprietary inputs no longer exist, in which case the adaptation can either cease to operate
or its modus operandi may be applied to a novel set of inputs. However, the adaptation’s
evolved domain of application need not disappear, it may simply contract or even
expand. In the case of domain expansion, the adaptation can continue to perform its
evolved function, yet simultaneously operate on novel inputs. Here it will help to make
use of additional distinctions. Millikan (1984) has made a distinction between an
adaptation’s proper function – the effects that it was designed by natural selection to
bring about – and an adaptation’s actual function – the effects that it does in fact bring
about. Sperber (1994) further elaborated Millikan’s proposal by distinguishing between
19
an adaptation’s proper domain – the range of situations (contents) the adaptation evolved
to apply to – and the adaptation’s actual domain – the range of situations (contents) that
the adaptation applies to. The proper function / domain of an adaptation is a matter of
historical fact, it does not change as the environment changes, unless, of course, one is
talking about long periods of change over which time natural selection has had time to
alter the constitution of the adaptation accordingly. It is the actual function / domain of an
adaptation that is potentially much more fluid and liable to change with environmental
changes. So to rephrase, as the environment changes, the actual function / domain of the
mechanism can contract, perhaps even to nothing; it can expand beyond the proper
function / domain; or it can shift to entirely new functions / domains.
When I speak of an adaptation as having largely been co-opted, I mean that the
adaptation’s modus operandi is still largely in evidence – i.e., the adaptation is not
dysfunctional. (To avoid conflating dysfunctions with adaptations with intact modus
operandi, but altered domains of application, I will limit my discussion to changes in an
adaptation’s actual domain, ignoring its actual function). Since the modus operandi of the
adaptation more or less intact, the resulting behavior will display complexly organized
functionality. However, in the case of broadened or displaced actual domains, the
‘adaptation’ is in fact, doing something novel, something that it was not selected for,
hence it would perhaps be best to speak of the resulting trait as being a byproduct and not
an adaptation. With broadened domains, one could continue to speak of the adaptation in
its proper domain while referring to the extended, novel uses of the adaptation as being a
byproduct of the adaptation.
This class of byproducts, ‘adaptations’ with extended or displaced actual domains
of application arguably constitute the primary source of exadaptations. They are
problematic for adaptationists because, owing to their relatively intact modus operandi,
they appear very much like adaptations – they perform complexly, functionally integrated
operations – but because the domain of application is novel, i.e. they lack the right
evolutionary pedigree, they are not adaptations. This is not to say that any time there is an
environmental change, exadaptations will result. In many cases, the end result will be
dysfunction. Because functionality is to some extent preserved with exadaptations,
species with some control over their environment may choose to augment these novel
functions or even bring about entirely new functions without the aid of prior
environmental change. Humans are very adept at altering their environment to suit their
ends. But humans also appear rather unique in having some grasp of the contents of their
own minds as well (Karmiloff-Smith, 1992). Hence, humans are perhaps uniquely
positioned to enhance and shift the application of their adaptations, including mental
adaptations, to new ends, giving rise to what Sperber (1994) has termed the cultural
domain of an adaptation. Consider one evolutionarily novel cultural innovation, written
language. Written language clearly is built on a foundation provided by a prior
adaptation, spoken language (Pinker, 1994). Spoken language typically remains intact in
those who can read and write, but the actual domain of this adaptation has been extended
by environmental props, written text, that have been devised, refined and culturally
transmitted by humans. Several cognitive anthropologists have suggested that that written
language is not unique in this respect, that many cultural phenomena and individual
expertise originate in this way, as novel applications of psychological adaptations (Atran,
1990; Boyer, 1994, 2003; Sperber, 1994, 2001; Sperber & Hirschfeld, 2004). Indeed,
20
several evolutionary psychologists have also argued that social and cultural phenomena
such as erotica (Salmon & Symons, 2003), law (Fiddick, 2004), religion (Kirkpatrick,
1999), and the concept of race (Cosmides, Tooby, Kurzban, 2003; Gil-White, 2001;
Kurzban, Tooby, & Cosmides, 2001) are extended or displaced applications of
adaptations.
Add Dehaene (1997) to this list for arithmetic
Exaptation as a theoretical diversion
Exaptation, Gould (1991) contended, is precisely the concept that evolutionary
psychologists need to make sense of evolutionarily novel cultural phenomena. Yet, across
numerous scientific investigations of cultural phenomena as diverse as literature (Salmon
& Symons, 2003), religion (Boyer, 1994, 2003; Kirkpatrick, 1999) and science (Atran,
1990), the phenomena under investigation are traced back to adaptations by means of a
common mode of mental operation – a characteristic modus operandi – with minimal
reference if any made to the current utility of the trait (and far less still to utility in terms
of enhanced reproductive success). Nor is it surprising that this should be the case, for the
concept of exaptation suffers from precisely the same defects as the adaptivist program.
Namely, investigations of current utility provide little insight into the structure of the trait
under investigation (Symons, 1990). It is the ability to explain the structure and
organization of a cultural phenomenon that many social scientists are interested in, not
demonstrations of enhanced reproductive success, which is primarily of parochial
interest. Like their colleagues operating from different theoretical frameworks, what these
cognitive anthropologists and evolutionary psychologists seek to understand is the
structure and organization of the phenomena under investigation. Where they differ from
their colleagues is in proposing that these phenomena bear a noncoincidental resemblance
to traits that are arguably adaptations. What they need is not the concept of exaptation,
but the concept of exadaptation.
The criticisms that I have raised about exaptations are not new. Buss et al. (1998)
have put forward similar and more detailed criticisms of the concept of exaptations.
However, arguing against the theoretical coherence and practical utility of the concept
does little to address the problem of evolutionarily novel functional design and critiques
of exaptation (e.g., Andrews, Gangestad, & Matthews, 2002; Buss et al., 1998) have
typically offered little in the way of guidance for dealing with the problem. Instead the
tendency has been an attempt to defang exaptation by casting it as a more onerous
concept than adaptation by, for example, arguing that the postulation of an exaptive
hypothesis requires one to first consider and then rule out adaptationist hypotheses. While
this is may be true in theory, scientific progress routinely advances in much smaller
measures, for truth be told, adaptationists rarely establish that a particular trait exhibits
special design, for example. They may strive for such evidence, but whether or not they
ever convincingly reach it is another matter. Moreover, some pieces of the empirical
puzzle may be far more important in keeping a project alive than others, so while it be the
case that exaptations pose a greater evidentiary burden, an immediate grasp that a
particular trait lacks the right sort of history may be all that is required to sustain an
exaptive hypothesis. Unless, of course, there is some rival account of evolutionarily novel
21
traits. Again, what is required is not just the concept of exadaptations or co-opted
adaptations, but a research program for dealing with them.
What do evolutionary psychologists have to gain from the modules and metaphors
program?
What do evolutionary psychologists have to gain from the modules and metaphors
program?
Notes on Gauthier
Anyway, I recall you mentioning that when autistics are competent at recognizing /
remembering faces, they process them in different ways than normals. Is this correct and
if so, could you possibly supply me some references. Here's why I'm curious. I'm writing
up the presentation that I gave last fall in Ottawa. One of the things that I argued then was
that rather than arguing against the domain specificity of face processing with her greeble
studies, Isabel Gauthier has in fact co-opted the face processing mechanism. Indeed, the
more she shows that greeble recognition is like face recognition, the more she paints
herself into a corner. Why? Well, this is where the autistism findings, if I recall what you
said correctly, come into play. The autism results show that the specific mode of
cognitive processing associated with faces in normals is not driven by the stimuli.
Autistics process exactly the same faces as normals do, but they process them in different
ways. Hence, to be a competent face processor does not mean that you will display
inversion effects and the like. Inversion effects are not a property of the stimulus, but of
the mind that processes the stimuli. So too the extent that greeble experts display the
peculiarities of normal face processing they appear to be invoking the same cognitive
mechanisms, when conceivably they could have invoked different cognitive mechanisms
-- i.e. those used by autistics. Hence, it would seem to me that all Gauthier has shown is
that greeble experts use their face mechanisms to recognize greeble. Now this might seem
to have a residual downside to this in that face mechanisms do not process faces and
faces alone. However, I can't see this as being a particularly damning critique of the
modularity (specialization of face processing). Still, it is not as bad as it first seems, since
not everyone uses their face mechanisms to process greebles, only greeble experts -- i.e.,
you really have to work at it to trick the face mechanisms to process greebles, a little
tweaking is required to get it going. Again, this is exactly the sort of developmental
trajectory one would expect if you trying to get a mechanism to do something it wasn't
designed to do.
I have argued that the modules and metaphors program is not simply compatible with
the practice of evolutionary psychology, but that it is actually dependent upon
evolutionary psychology to provide a source of scientific insight into the base domains of
concepts and inferences that are available for co-opting. However, this need not mean
22
that the benefits are reciprocal. What are evolutionary psychologists to gain from the
modules and metaphors program? The benefits, I will argue, are several.
Explaining expertise
Expertise, as I have suggested, represents a viable alternative account of adaptive
design and hence one of the most important theoretical challenges to evolutionary
psychology. Fortunately, the modules and metaphors program provides an alternative
account of expertise. Consider in a bit more detail this time, the debate over face
processing. One of the most prominent arguments against the existence of specialpurpose facial recognition mechanisms is that many of the same phenomena have been
taken as evidence for the distinctiveness of facial recognition, such as configural
processing, also are purportedly displayed by people trained to recognize individual
“greebles” – imaginary 3-D creatures that are distinguished on the basis of the relations
of their features as opposed to distinctive parts, i.e. their configural properties (Gauthier
& Tarr, 1997). For example, facial features (e.g. the eyes or nose) studied in the context
of a whole face are recalled best when they are later recalled in the context of the same
face as opposed to the parts in isolation or a configurally transformed face (e.g., the
mouth placed lower on the face) suggesting that facial features are not represented
independently, but holistically as part of a whole face. By contrast. no advantage is
observed for the recognition of house features or inverted face features in configurally
intact targets (Tanaka & Farah, 1993). Gauthier and Tarr (1997) reported the same
upright, intact configuration advantage for the recognition of greeble features in greeble
experts as opposed to greeble novices (see also Gauthier & Nelson, 2001, for a review of
the expertise findings).
The process of acquiring expertise, however, is entirely understood. One way that
people could become experts, according to the modules and metaphors program, is by
recruiting a pre-existing module that was designed by natural selection for some other
function. Indeed, such a process would be expected to result in precisely the “qualitative
shift in processing” that Gauthier and Tarr (1997) take as indicative of expertise.
Moreover, the more the domain of acquired expertise resembles the domain of a preexisting module, the more likely that that module will get recruited. Again, greebles were
designed precisely to draw upon the same configural processing that face recognition
requires (Gauthier & Tarr, 1997). Moreover, if in the process of becoming a greeble
expert, people simply recruit face processing modules, then precisely the same neural
structures should underlie face recognition and greeble recognition, which, it turns out, is
the case (Gauthier, Tarr, Anderson, Skudlarski, & Gore, 1999).
Of course, the explanation for these findings that Gauthier and her colleagues would
like to give is that face recognition is really a form of acquired expertise, but the results
could also be interpreted in precisely the opposite direction from the perspective of the
modules and metaphors program, namely that in the process of becoming a greeble
expert, Gauthier’s subjects have simply co-opted their face processing mechanisms (cf.
McKone & Kanwisher, in press). How can we tease these two proposals apart?
Empirically, it is could be fairly difficult to distinguish between the proposals. For
example, while one might speculate that a face processing mechanism should presumably
show a face advantage in terms of accuracy or robustness of configural effects, there is a
23
considerable confound in that most people will have considerably more experience
processing faces than greebles. Ultimately, the most persuasive arguments are likely to be
theoretical. Unless advocates of acquired expertise want to argue that all expertise,
regardless of the domain involves the same mental processes and recruits the same
neurological structures, then they are going to have to admit that they are implicitly
arguing for a different collection of innate faculties. If not a face-specific faculty, then a
configural processing faculty and the burden then falls upon the advocates of the
expertise position to explain why natural selection would have favored the evolution of
such a faculty of mind. What plausible selection pressures could have favored the
evolution of configural processing, per se, when it primarily seems to be invoked by
individual bird, car, face and greeble recognition (see Gauthier & Nelson, 2001, for a
defense of the position that expert bird, car, face and greeble recognition all recruit the
same mental / neurological structures)? Cast in this evolutionarily light, it seems far more
parsimonious to claim that configural processing is simply a design feature of an evolved
face recognition mechanism.
Drawing defensible boundaries around adaptationist proposals
The modules and metaphors program can potentially help evolutionary psychologists
from falling into the trap of trying to explain too much in terms of adaptive design.
Without a distinction between the proper domain of an evolved mechanism and its actual
metaphorical extension, evolutionary psychologists could be tempted to explain more
than is warranted by a consideration of the evolutionary history of an adaptation.
Consider, for example, the debate over Cosmides’ (1989) attempt to account for
reasoning about social exchanges and social laws with the same adaptationist
explanation. According to social contract theory, people possess an evolved “look for
cheaters” algorithm that is activated in situations involving social exchange, cooperation
for mutual benefit. In providing an evolutionary rationale for this proposal, Cosmides
(1989; Cosmides & Tooby, 1989, 1992) referred to evolutionary theories of reciprocal
altruism that suggested that reciprocal altruism could not evolve without the ability to
detect and punish cheaters (e.g., Axelrod & Hamilton, 1981; Trivers, 1971). These
evolutionary models invariably featured two agents potentially engaged in a reciprocal
exchange of benefits, yet Cosmides applied her account of cheater detection beyond the
confines of reciprocal exchange.
Cosmides (1989) tested her proposal using the well known Wason selection task in
which subjects are asked to reason about a conditional rule. As Cosmides rightly noted,
an offer to engage in social exchange can be phrased as a conditional rule of the form: If
you take the benefit, then you must pay the cost, and when social exchanges (which
Cosmides referred to a personal exchanges) are so phrased and embedded in the selection
task, performance on the task improved substantially. However, social contracts rules
such as this can also be used to describe situations in which no reciprocity or exchange of
benefits takes place. For example, Cosmides argued that the drinking age rule: If you
drink alcohol, then you must be at least 21 years old, is social contract and likewise
activates the proposed “look for cheaters” algorithm. Indeed, social law versions of social
contract rules – social contracts that do not involve social exchange – also reliably elicit
correct performance on the selection task.
24
Rather than arguing that these social laws are metaphorical extensions of social
exchanges, brought about straightforwardly by similar rules, Cosmides provided a
generalized account of reasoning about social contracts that blurred the distinction
between personal exchanges (proper social exchanges) and social laws, like the drinking
age rule. Cheng and Holyoak (1989) correctly noted this apparent inconsistency in
Cosmides’ formulation of the theory. However, rather than dealing with the problem
honestly by either formulating an alternative evolutionary theory of cooperation that
extended beyond social exchanges or proposing a distinction between the proper and
actual domain of application of the hypothesized mechanisms, Fiddick, Cosmides, and
Tooby (2000, Appendix A) simply asserted that there is no evolutionary justification for
distinguishing between social exchanges and social laws. There are, in fact, good grounds
for skepticism. To begin with, the very theories that Cosmides’ (1985, 1989; Cosmides &
Tooby, 1989) cited make no reference to anything like social laws. They deal primarily
with social exchanges involving two parties, both of which receive a benefit. Fiddick et
al. (2000) also objected that Cheng and Holyoak (1989) narrowly interpreted exchanges
to mean the exchange of objects. This is a mischaracterization of Cheng and Holyoak’s
argument. Their argument with respect to rules such as the drinking age rule is not that
age is not an object, but that it is not a benefit to the other party.
Regardless of whether initially casting the theory in terms of reciprocal exchange was
too narrow a focus (cf. Cummins, 1999; Hiraishi & Hasegawa, 2001), the attempt to
explain all performance displaying the same modus operandi as being part of the proper
function of the proposed mechanism was clearly an error and resulted avoidable
confusion and skepticism regarding the claims of evolutionary psychology. A better
approach would have been to limit the scope of one’s adaptationist arguments and
invoked the something like the modules and metaphors framework beyond defendable
adaptationist boundaries.
Gaining insight from culture and expertise
The modules and metaphors program suggests the means by which the students of
culture and expertise can potentially apply evolutionary psychological findings to their
own phenomena of interest even when what they are studying is not even conceivably an
adaptation. This is likely to prove most profitable when the phenomenon that they are
studying bears some evidence of complex functionality and, hence, may reflect co-opted
functional design. The benefits, however, do not only flow one way, from evolutionary
psychology to cultural and expertise studies. If one accepts that cultural phenomena and
expertise can be reflections of functional design, then it becomes possible to study
functional design via its metaphorical extension. Not only is there a long cultural tradition
in art, literature, and religion – not to mention the formal studies of these phenomena –
attempting to make the ineffable manifest, but sometimes cultural products provide
unique insights into the minds that make them that would not otherwise be available.
Given the inevitable constraints that the conflicting interests of the sexes imposed on
observed mating behavior, the idealized worlds of romance and pornutopia provide
valuable insights into the mating psychology of human females and males that might not
otherwise be observable (Salmon & Symons, 2003). However, in using romance novels,
erotica and pornography to understand the minds that produced it, one is working within
25
the modules and metaphors program, only working backwards from metaphorical
extensions to the evolved modules presumably give shape to the cultural products.
Critiques of exaptation (Andrews et al., 2002; Buss et al., 1998) would leave one with
the impression that this could be a particularly perilous enterprise, for not only would one
first have to establish reasonable grounds for assuming the existence of a mental
adaptation, but one would also have to argue that the cultural phenomenon or instance of
expertise under investigation is a metaphorical extension of that adaptation, with the
implication being that it would be easier simply to pursue the adaptationist program.
However, no science worthy of the name is transparent, even mental phenomena are not
readily transparent to the researchers studying them and all the more so when the mental
structures in question are modular with little cognitive access. Hence, the speculative
hypothesis that some cultural phenomenon is the metaphorical extension of a mental
adaptation based upon the recognition of a common modus operandi could provide a
valuable source of insights into the structure and operation of the mental adaptation. By a
process of reflective equilibrium working from cultural trait to psychological trait and
vice versa, one can potentially refine one’s understanding of both the psychological trait
and the cultural phenomena that are likely extensions of it.
Conclusions
By providing an adaptationist alternative to exaptation, the modules and
metaphors program can hopefully put to rest a bad explanation for a real phenomenon.
That phenomenon is evolutionarily novel complex functionality, which is potentially
problematic for adaptationists since it challenges the priority of natural selection as the
source of natural design. However, through framework of the modules and metaphors
program, evolutionarily novel functional design can potentially be explained as the
metaphorical extension of prior adaptive designs.
26
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Footnotes
1
Here, as in the rest of the paper, I mean function in the nontechnical sense as a system
of parts working as a whole, typically to bring about some useful end with no implication
that use translates to reproductive success. When referring to functions in the
evolutionary biologist’s sense of the term I will refer to proper functions (Millikan, 1984)
as I will explain in more detail later.
33
Scraps
Many will undoubtedly associate the term with Fodor’s (1983) analysis of input systems
– i.e., perceptual systems and language. According to this analysis, modules are
characterized by a list of features with domain-specificity, informational encapsulation,
limited central access and a fixed neural architecture among the most important features.
By why privilege one analysis of modularity, especially when there exists a variety of
opinion on the matter (e.g, Barrett, in press; Chomsky, 1980; Jackendoff, 1987; Marr,
1982; Sperber, 1994). Perhaps it might seem inconsistent on my part sticking to a strict
definition of evolutionary psychology while asking for some leeway on the definition of
modularity, however there are important differences between the two situations and it
will be instructive to consider them. To begin with, the concept module or modularity
was in fairly wide circulation before Fodor published his analysis, so much so that
Chomsky (1980) could repeatedly use the term in a monograph intended for a general
audience without either defining or referencing the term. Cosmides and Tooby (1987, p.
283), on the other hand, explicitly referenced and defined the term evolutionary
psychology in what would be a foundational paper in the emerging field. More
importantly though, Fodor’s (1983) use of the term modularity was roughly comparable
to Chomsky’s (1983) use of the term, Marr’s (1982) use of the term, and so on. Goal of
Fodor’s analysis was, presumably to get at the essence of the mental kind “module,”
whereas the essence of Cosmides and Tooby’s (1987) analysis was to draw a distinction
between different styles of evolutionary theorizing. Hence, when evolutionary
psychology is later characterized in much broader terms (Heyes, 2003), such that it
includes not only research programs that were explicitly contrasted with evolutionary
psychology and whose practitioners publicly reject the label (Smith, Borgerhoff Mulder,
& Hill, 2000, 2001), but also behaviorism, an inclusion that both sides of this schism
would reject, then one is simply misapplying the term. However, when later analyses of
modularity are proposed and adopted, one is not necessarily misapplying the term. As
Sperber (1994, p. 42) remarks: “If modularity is a genuine natural property, then what it
consists of is a matter of discovery, not stipulation.”