Relative Long Bone Proportions and Developmental Stress in a Modern Thai Population
Kristen R. Rectenwald
North Carolina State University, Department of Sociology & Anthropology
Table 1. Select female correlations (right side v. LEH)
Introduction
Element/Stature
N
Proportional relationships inherent in body size and shape,
both within and between populations, offer considerable
information on the life-ways of past and present humans.
Research concerning relative, or scale-free, limb proportions has
revealed interesting patterns of variability with regards to
environment. Traditionally, these investigations examined
proximal and distal length differences by comparing brachial
(radius/humerus length) and crural (tibia/femur length) indices
from various populations. However, there have been no direct
attempts to correlate variability in limb proportion with unrelated
stress indicators. In response, this study examined the
relationship between long bone length ratios and linear enamel
hypoplasia (LEH) frequency – defects of enamel secretion directly
resulting from childhood stress.
Correlation
Coefficient
Humerus/Stature
39
-.256
Tibia/Stature
36
-.427
Hypothesis
• Limb segment proportions will be positively correlated with
the frequency of linear enamel hypoplasia, thus signifying the
variability of limb ratios with regard to stress
Radius/Stature
Femur/Stature
Distal/Proximal
Radius/Humerus
Tibia/Femur
37
37
41
39
p-value
.115
-.349
.034*
-.219
.168
-.223
-.334
.184
.009*
.038*
Table 2. Select male correlations (right side v. LEH)
Element/Stature
N
Correlation
Coefficient
Humerus/Stature
48
.086
.561
Femur/Stature
45
.119
.435
Radius/Stature
Tibia/Stature
Distal/Proximal
Radius/Humerus
Tibia/Femur
51
44
53
47
.141
.065
.138
-.202
p-value
.325
.676
.325
.173
Additional Research
• Which approach reveals more variability, brachial/crural
indices or relative bone length (element/stature)?
Background
Long Bone Proportions
• Limb length and stature vary:
~ Genetically due to climate/biomechanical evolution
~ Developmentally due to nutritional/disease stress
• Distal segments (radius & tibia) highly variable
• Proximal limb segments (humerus & femur) more stable
• Smaller-than-average proximal/distal ratios = more stress
Figure 1. Half of maxillary arcade with LEH (left) and without LEH (right)
Materials and Methods
Chiang Mai University Skeletal Collection , North Thailand
• Modern (20th century individuals)
• Females
~ N = 105, Mean Age = 66.6, Mean Stature = 153.6
• Males
~ N = 154, Mean Age = 64.8, Mean Stature = 165.4
• LEH Data Requirements (Duray 1996)
~ At least 6 total teeth, 3 anterior
~ LEH identified with 10x mag. Loupe
• Spearman’s rank correlation used to examine associations
Results
Relative length
• Distal segments (radius & tibia) significantly correlated with
developmental stress in females
• No obvious pattern in males
Distal/Proximal
• Significant difference in proximal & distal response to
developmental stress in female tibiae
• No obvious pattern in males
Conclusions
Distal limb length is positively correlated with LEH frequency
(and therefore developmental stress) in Thai females.
Sexually Dimorphic Response
• Females may express more variability in limbs because of
developmental focus on trunk stability (reproduction)
Brachial/Crural Indices v. Relative Bone Length
• Distal/proximal ratios do not allow for proximal variability
~ If proximal length decreases even slightly, distal change
may not register
• Relative bone length better reveals limb segment variability
Linear Enamel Hypoplasia
• Lines of thin enamel appearing on permanent teeth during
development (childhood)
• Direct response to periods of environmental stress
• Development pattern entirely unrelated to limbs
~ Serves as independent proxy for childhood stress
Figure 2. Brachial Index =
Radius/Humerus
Figure 3. Crural Index =
Tibia/Femur
This study supports the use of limb segment proportion to
examine stress
Selected Literature
Auerbach B. & Sylvester A. 2011 Allometry and Apparent Paradoxes in Human Limb Proportions: Implications for Scaling Factors. American Journal of Physical Anthropology 144:382-391.
Duray S. 1996 Dental Indicators of Stress and Reduced Age at Death in Prehistoric Native Americans. American Journal of Physical Anthropology 99:275-286.
Holliday T. 1999 Bracial and Crural indices of European Late Upper Paleolithic and Mesolithic Humans. Journal of Human Evolution 36:549-566.
Holliday T. & Ruff C. 2001 Relative Variation in Human Proximal and Distal Limb Segment Lengths. American Journal of Physical Anthropology 116:26-33.
King T., Humphrey L. & Hillson S. 2005 Linear Enamel Hypoplasias as Indicators of Systemic Physiological Stress: Evidence from Two Known Age-at-Death and Sex Populations from Postmedieval London. American Journal of Physical Anthropology 128:547-559.
Images
http://www.boneclones.com
http://leeannbrady.com/tag/cementation
Otis Historical Archives of the National Museum of Health and Medicine
http://www.flickr.com/photos/medicalmuseum/3380484445/