Skeletal evidence for variable patterns of handedness in chimpanzees, human hunter-gatherers, and recent British populations

Multiproxy bioarchaeological data reveals interplay between growth, diet and population dynamics across the transition to farming in the central Mediterranean

The transition to farming brought on a series of important changes in human society, lifestyle, diet and health. The human bioarchaeology of the agricultural transition has received much attention, however, relatively few studies have directly tested the interrelationship between individual lifestyle factors and their implications for understanding life history changes among the first farmers. We investigate the interplay between skeletal growth, diet, physical activity and population size across 30,000 years in the central Mediterranean through a 'big data' cross-analysis of osteological data related to stature (n = 361), body mass (n = 334) and long bone biomechanics (n = 481), carbon (δ13C) and nitrogen (δ15N) stable isotopes (n = 1986 human, n = 475 animal) and radiocarbon dates (n = 5263). We present the observed trends on a continuous timescale in order to avoid grouping our data into assigned 'time periods', thus achieving greater resolution and chronological control over our analysis. The results identify important changes in human life history strategies associated with the first farmers, but also highlight the long-term nature of these trends in the millennia either side of the agricultural transition. The integration of these different data is an important step towards disentangling the complex relationship between demography, diet and health, and reconstruct life history changes within a southern European context. We believe the methodological approach adopted here has broader global implications for bioarchaeological studies of human adaptation more generally.

A comparative study of robusticity indices of long bones among hunter-gatherers and early agro-pastoral groups of India

OBJECTIVES

Diaphyseal robusticity and cross-sectional shapes of the bone tissues are influenced by mechanical loading history. It changes according to work demand on the body. It is the objective of this study to identify the shifts in the modes of subsistence, activities and mobility patterns through the comparison of the shape and strength of bone diaphyses among the Mesolithic, Chalcolithic and Harappan populations of India.

MATERIALS AND METHODS

For the analysis, 7 sites including 2 from Mesolithic (8000-4000 bc), 2 from Chalcolithic (2000-700 bc) and 3 from Harappan (3500-1800 bc) contexts are considered. The ratio obtained from the maximum length of the bones to their girth (at 50% or 35% from the distal end) and that from anterior-posterior and medio-lateral diameters were calculated (following Martin and Saller codes, 1957) to understand certain functional adaptations and stress markers on preserved long bones. Independent-sample T-tests and ANOVA were applied to detect mean differences of statistical significance within and between cultures.

RESULTS

The robusticity indices obtained from the humeri increase from the hunting-gathering phase (M/F; 19.39/18.45) to the Chalcolithic phase (M/F; 21.99/19.39) showing a slight drop in the Harappan phase (M/F; 18.58/18.37). The right humeri of Mesolithic females show a directional asymmetry of length (4.08%-5.13%) while that in males reach up to 26.09% indicating right-dominant lateralization. In the Harappan phase, females show a greater value for the right ranging from 0.31% to 3.07%. The femoral robusticity of females increases from 11.42 in hunting-gathering societies to 13.28 in Harappan times while mid-shaft of the Mesolithic population clearly shows greater loading along the anterior-posterior (A-P) plane as the index in most cases exceeds 100. There are significant differences among males and females within each group in terms of the indices but significant differences could be discerned between the Mesolithic, Chalcolithic and Harappan populations in case of tibiae, radii and ulnae only.

CONCLUSION

The occupation patterns certainly changed as humans became a food-producer from a hunter-gatherer. Occupations involving the extensive flexion and extension of upper limbs in the Chalcolithic period increase particularly in the Harappan phase. Sedentism gave rise to roundness of the femur and reduced the magnitude of lateralization. While equal level of mobility can be traced in case of both the sexes before the advent of agriculture, this distinction increases between the males and females in the agro-pastoral phases.

Caring for the injured: Exploring the immediate and long-term consequences of injury in medieval Cambridge, England

OBJECTIVE

To combine paleopathological and biomechanical analysis to reconstruct the impact that a severe skeletal injury had on an individual's ability to function and participate in medieval society.

MATERIALS

Three medieval individuals from Cambridge, England with ante-mortem fractures to the lower limb were analyzed.

METHODS

Plain X-rays were used to determine the degree of malunion, rotation and overlap of each fracture. Cortical bone architecture of the injured individuals and 28 uninjured controls were analyzed using micro-computed tomography (µCT). Clinical and functional consequences were examined using the Bioarcheology of Care framework.

RESULTS

The mechanism of injury, the secondary complications, and the extent of the care received was reconstructed for each individual. Bilateral asymmetry in the cortical bone architecture revealed the long-term alterations to each individual's gait.

CONCLUSION

Each of these individuals survived a severe injury resulting in chronic physical impairment, though not all would have been considered 'disabled'.

SIGNIFICANCE

This research contributes to the discussion about medieval care provision and social constructions of disability by illustrating how an interdisciplinary approach provides insight into the experiences of those with physical impairments. The integration of µCT imaging within the Bioarcheology of Care model is a novel approach with great potential for application across the field.

LIMITATIONS

Biomechanical analysis was restricted to cortical geometry.

SUGGESTIONS FOR FUTURE RESEARCH

Further study of bilateral asymmetry in trabecular architecture could complement our understanding of altered loading modalities in past societies.

Buried with their Buckles On: Clothed Burial at the Augustinian Friary, Cambridge

GIRDLE BUCKLES ASSOCIATED with several groups of burials at the later-medieval Augustinian friary in Cambridge indicate that clothed burial was common, with a much higher prevalence than usual for the period. The clothed burial was highly regularised, in terms of both the garments worn and the types of buckles used, and apparently limited to members of the Augustinian Order. The buckles were primarily supplied by the friary, rather than representing individual choices, and there is evidence that the girdles that individuals were buried with were those they used in life. These buckles functioned on several levels, as symbols of both corporate and personal identity. Discoveries at other English Augustinian friaries demonstrate specific typological parallels, indicating broader connections, networks and identities. Although buckles are common late-medieval items, those from the Cambridge Augustinian friary present a unique opportunity to contextualise their use by one segment of society.

Early Holocene morphological variation in hunter-gatherer hands and feet

Background

The Windover mortuary pond dates to the Early Archaic period (6,800–5,200 years ago) and constitutes one of the earliest archaeological sites with intact and well-preserved human remains in North America. Unlike many prehistoric egalitarian hunter-gatherers, the Windover people may not have practiced a sex-based division of labor; rather, they may have shared the load. We explore how mobility and subsistence, as reconstructed from archaeological data, influenced hand and foot bone morphology at Windover.

Methods

We took length and width measurements on four carpal bones, four tarsal bones, and load-bearing tarsal areas (calcaneus load arm, trochlea of the talus). We analyzed lateralization using side differences in raw length and width measurements. For other hypothesis testing, we used log transformed length-width ratios to mitigate the confounding effects of sexual dimorphism and trait size variation; we tested between-sex differences in weight-bearing (rear foot) and shock-absorbing (mid foot) tarsal bones and between-sex differences in carpal bones.

Results

We identified no significant between-sex differences in rear and midfoot areas, suggesting similar biomechanical stresses. We identified no significant between-sex differences in carpal bones but the test was under-powered due to small sample sizes. Finally, despite widespread behavioral evidence on contemporary populations for human hand and foot lateralization, we found no evidence of either handedness or footedness.

Discussion

The lack evidence for footedness was expected due its minimal impact on walking gait but the lack of evidence for handedness was surprising given that ethnographic studies have shown strong handedness in hunter-gatherers during tool and goods manufacture. The reconstructed activity patterns suggested both sexes engaged in heavy load carrying and a shared division of labor. Our results support previous findings—both sexes had stronger weight-bearing bones. Male shock-absorbing bones exhibited a trend towards greater relative width (suggesting greater comparative biomechanical stress) than females which may reflect the typical pattern of male hunter-gatherers engaging in walking greater distances at higher speeds than females. While there were no significant between-sex differences in carpal bones (supporting a shared work load model), females exhibited greater variation in index values, which may reflect a greater variety of and specialization in tasks compared to males. Because carpals and tarsals are so well-preserved at archaeological sites, we had surmised they might be useful proxies for activity in the absence of well-preserved long bones. Tarsals provide a stronger signal of past activity and may be useful in the absence of, or in addition to, preferred bones. Carpals, however, may not be useful as the effect size of biomechanical stress (in this study at least) is low and would require larger samples than may be possible at archaeological sites.

Trabecular bone patterning across the human hand

Hand bone morphology is regularly used to link particular hominin species with behaviors relevant to cognitive/technological progress. Debates about the functional significance of differing hominin hand bone morphologies tend to rely on establishing phylogenetic relationships and/or inferring behavior from epigenetic variation arising from mechanical loading and adaptive bone modeling. Most research focuses on variation in cortical bone structure, but additional information about hand function may be provided through the analysis of internal trabecular structure. While primate hand bone trabecular structure is known to vary in ways that are consistent with expected joint loading differences during manipulation and locomotion, no study exists that has documented this variation across the numerous bones of the hand. We quantify the trabecular structure in 22 bones of the human hand (early/extant modern Homo sapiens) and compare structural variation between two groups associated with post-agricultural/industrial (post-Neolithic) and foraging/hunter-gatherer (forager) subsistence strategies. We (1) establish trabecular bone volume fraction (BV/TV), modulus (E), degree of anisotropy (DA), mean trabecular thickness (Tb.Th) and spacing (Tb.Sp); (2) visualize the average distribution of site-specific BV/TV for each bone; and (3) examine if the variation in trabecular structure is consistent with expected joint loading differences among the regions of the hand and between the groups. Results indicate similar distributions of trabecular bone in both groups, with those of the forager sample presenting higher BV/TV, E, and lower DA, suggesting greater and more variable loading during manipulation. We find indications of higher loading along the ulnar side of the forager sample hand, with high site-specific BV/TV distributions among the carpals that are suggestive of high loading while the wrist moves through the 'dart-thrower's' motion. These results support the use of trabecular structure to infer behavior and have direct implications for refining our understanding of human hand evolution and fossil hominin hand use.

Trabecular architecture in the thumb of Pan and Homo: implications for investigating hand use, loading, and hand preference in the fossil record

OBJECTIVES

Humans display an 85-95% cross-cultural right-hand bias in skilled tasks, which is considered a derived behavior because such a high frequency is not reported in wild non-human primates. Handedness is generally considered to be an evolutionary byproduct of selection for manual dexterity and augmented visuo-cognitive capabilities within the context of complex stone tool manufacture/use. Testing this hypothesis requires an understanding of when appreciable levels of right dominant behavior entered the fossil record. Because bone remodels in vivo, skeletal asymmetries are thought to reflect greater mechanical loading on the dominant side, but incomplete preservation of external morphology and ambiguities about past loading environments complicate interpretations. We test if internal trabecular bone is capable of providing additional information by analyzing the thumb of Homo sapiens and Pan.

MATERIALS AND METHODS

We assess trabecular structure at the distal head and proximal base of paired (left/right) first metacarpals using micro-CT scans of Homo sapiens (n = 14) and Pan (n = 9). Throughout each epiphysis we quantify average and local bone volume fraction (BV/TV), degree of anisotropy (DA), and elastic modulus (E) to address bone volume patterning and directional asymmetry.

RESULTS

We find a right directional asymmetry in H. sapiens consistent with population-level handedness, but also report a left directional asymmetry in Pan that may be the result of postural and/or locomotor loading.

CONCLUSION

We conclude that trabecular bone is capable of detecting right/left directional asymmetry, but suggest coupling studies of internal structure with analyses of other skeletal elements and cortical bone prior to applications in the fossil record.

The impact of subsistence changes on humeral bilateral asymmetry in Terminal Pleistocene and Holocene Europe

Analyses of upper limb bone bilateral asymmetry can shed light on manipulative behavior, sexual division of labor, and the effects of economic transitions on skeletal morphology. We compared the maximum (absolute) and directional asymmetry in humeral length, articular breadth, and cross-sectional diaphyseal geometry (CSG) in a large (n > 1200) European sample distributed among 11 archaeological periods from the Early Upper Paleolithic through the 20(th) century. Asymmetry in length and articular breadth is right-biased, but relatively small and fairly constant between temporal periods. Females show more asymmetry in length than males. This suggests a low impact of behavioral changes on asymmetry in length and breadth, but strong genetic control with probable sex linkage of asymmetry in length. Asymmetry in CSG properties is much more marked than in length and articular breadth, with sex-specific variation. In males, a major decline in asymmetry occurs between the Upper Paleolithic and Mesolithic. There is no further decline in asymmetry between the Mesolithic and Neolithic in males and only limited variation during the Holocene. In females, a major decline occurs between the Mesolithic and Neolithic, with resulting average directional asymmetry close to zero. Asymmetry among females continues to be very low in the subsequent Copper and Bronze Ages, but increases again in the Iron Age. Changes in female asymmetry result in an increase of sexual dimorphism during the early agricultural periods, followed by a decrease in the Iron Age. Sexual dimorphism again slightly declines after the Late Medieval. Our results indicate that changes in manipulative behavior were sex-specific with a probable higher impact of changes in hunting behavior on male asymmetry (e.g., shift from unimanual throwing to use of the bow-and-arrow) and food grain processing in females, specifically, use of two-handed saddle querns in the early agricultural periods and one-handed rotary querns in later agricultural periods.

Fluctuating and directional asymmetry in the long bones of captive cotton-top tamarins (Saguinus oedipus)

OBJECTIVES

Skeletal asymmetries reflect developmental stability and mechanical, functional, and physiological influences on bone growth. In humans, researchers have documented the greatest limb bone bilateral asymmetry in diaphyseal breadths, with less asymmetry in articular and maximum length dimensions. However, it remains unclear as to whether the pattern observed for humans is representative of nonhuman primates, wherein bilateral loading may minimize directional asymmetry. This study adds to the small body of asymmetry data on nonhuman primates by investigating patterns of long bone asymmetry in a skeletal sample of Saguinus oedipus (cotton-top tamarin).

MATERIALS AND METHODS

Humeri, radii, ulnae, femora, and tibiae of 76 adult captive cotton-top tamarin skeletons (48 males, 28 females) were measured bilaterally. We included maximum length, midshaft diaphyseal breadths, and at least one articular measurement for each bone to assess directional (DA) and fluctuating asymmetry (FA) in each dimension.

RESULTS

Most dimensions exhibit significant FA, and very few have significant DA; DA is limited to the lower limb, especially in knee dimensions. Overall, the magnitudes of asymmetry in tamarins have a consistent ranking that follows the same pattern as found in humans.

DISCUSSION

This first study of DA and FA among multiple dimensions throughout the limbs of a non-hominoid primate suggests that previously-reported patterns of human bilateral asymmetry are not exclusive to humans. The results further indicate potential underlying differences in constraints on variation within limb bones. While processes shaping variation await further study, our results argue that different long bone dimensions may reflect dissimilar evolutionary processes.

Forelimb preferences in human beings and other species: multiple models for testing hypotheses on lateralization

Functional preferences in the use of right/left forelimbs are not exclusively present in humans but have been widely documented in a variety of vertebrate and invertebrate species. A matter of debate is whether non-human species exhibit a degree and consistency of functional forelimb asymmetries comparable to human handedness. The comparison is made difficult by the variability in hand use in humans and the few comparable studies conducted on other species. In spite of this, interesting continuities appear in functions such as feeding, object manipulation and communicative gestures. Studies on invertebrates show how widespread forelimb preferences are among animals, and the importance of experience for the development of forelimb asymmetries. Vertebrate species have been extensively investigated to clarify the origins of forelimb functional asymmetries: comparative evidence shows that selective pressures for different functions have likely driven the evolution of human handedness. Evidence of a complex genetic architecture of human handedness is in line with the idea of multiple evolutionary origins of this trait.

Human evolution. Human-like hand use in Australopithecus africanus

The distinctly human ability for forceful precision and power "squeeze" gripping is linked to two key evolutionary transitions in hand use: a reduction in arboreal climbing and the manufacture and use of tools. However, it is unclear when these locomotory and manipulative transitions occurred. Here we show that Australopithecus africanus (~3 to 2 million years ago) and several Pleistocene hominins, traditionally considered not to have engaged in habitual tool manufacture, have a human-like trabecular bone pattern in the metacarpals consistent with forceful opposition of the thumb and fingers typically adopted during tool use. These results support archaeological evidence for stone tool use in australopiths and provide morphological evidence that Pliocene hominins achieved human-like hand postures much earlier and more frequently than previously considered.

Divergence in male and female manipulative behaviors with the intensification of metallurgy in Central Europe

Humeral morphology has been shown to reflect, in part, habitual manipulative behaviors in humans. Among Central European agricultural populations, long-term social change, increasing task specialization, and technological innovation all had the potential to impact patterns of habitual activity and upper limb asymmetry. However, systematic temporal change in the skeletal morphology of agricultural populations in this region has not been well-characterized. This study investigates diachronic patterns in humeral biomechanical properties and lengths among 174 adult Central European agriculturalists through the first ∼ 5400 years of farming in the region. Greater asymmetry in biomechanical properties was expected to accompany the introduction of metallurgy, particularly in males, while upper limb loading patterns were expected to be more similar between the Bronze and Iron Ages. Results revealed a divergence in the lateralization of upper limb biomechanical properties by sex between the Early/Middle Neolithic and Early/Middle Bronze Age. Neolithic females had significantly more variable properties than males in both humeri, while Bronze Age female properties became homogeneous and very symmetrical relative to the right-biased lateralization of contemporaneous males. The Bronze Age to Iron Age transition was associated with morphological change among females, with a significant increase in right-biased asymmetry and a concomitant reduction in sexual dimorphism. Relative to biomechanical properties, humeral length variation and asymmetry were low though some significant sexual dimorphism and temporal change was found. It was among females that the lateralization of humeral biomechanical properties, and variation within them, changed most profoundly through time. This suggests that the introduction of the ard and plow, metallurgical innovation, task specialization, and socioeconomic change through ∼ 5400 years of agriculture impacted upper limb loading in Central European women to a greater extent than men.