Jay T. Stock

Habitual throwing and swimming correspond with upper limb diaphyseal strength and shape in modern human athletes

Variation in upper limb long bone cross-sectional properties may reflect a phenotypically plastic response to habitual loading patterns. Structural differences between limb bones have often been used to infer past behavior from hominin remains; however, few studies have examined direct relationships between behavioral differences and bone structure in humans. To help address this, cross-sectional images (50% length) of the humeri and ulnae of university varsity-level swimmers, cricketers, and controls were captured using peripheral quantitative computed tomography. High levels of humeral robusticity were found in the dominant arms of cricketers, and bilaterally among swimmers, whereas the most gracile humeri were found in both arms of controls, and the nondominant arms of cricketers. In addition, the dominant humeri of cricketers were more circular than controls. The highest levels of ulnar robusticity were also found in the dominant arm of cricketers, and bilaterally amongst swimmers. Bilateral asymmetry in humeral rigidity among cricketers was greater than swimmers and controls, while asymmetry for ulnar rigidity was greater in cricketers than controls. The results suggest that more mechanically loaded upper limb elements--unilaterally or bilaterally--are strengthened relative to less mechanically loaded elements, and that differences in mechanical loading may have a more significant effect on proximal compared to distal limb segments. The more circular humerus in the dominant arm in cricketers may be an adaptation to torsional strain associated with throwing activities. The reported correspondence between habitual activity patterns and upper limb diaphyseal properties may inform future behavioral interpretations involving hominin skeletal remains.

Intensity, Repetitiveness, and Directionality of Habitual Adolescent Mobility Patterns Influence the Tibial Diaphysis Morphology of Athletes

Mobility patterns affect the loads placed on the lower limbs during locomotion and may influence variation in lower limb diaphyseal robusticity and shape. This relationship commonly forms the basis for inferring mobility patterns from hominin fossil and skeletal remains. This study assesses the correspondence between athletic histories, varying by loading intensity, repetition and directionality, measured using a recall questionnaire, and peripheral quantitative computed tomography-derived measurements of tibial diaphysis rigidity and shape. Participants included male university varsity cross-country runners (n = 15), field hockey players (n = 15), and controls (n = 20) [mean age: 22.1 (SD +/- 2.6) years]. Measurements of tibial rigidity (including J, %CA, Imax, Imin, and average cortical thickness) of both runners and field hockey players were greater than controls (P < or = 0.05). Differences in tibial shape (Imax/Imin, P < or = 0.05) between runners and hockey players reflect pronounced maximum plane (Imax) rigidity in runners, and more symmetrical hypertrophy (Imax, Imin) among hockey players. This corresponds with the generally unidirectional locomotor patterns of runners, and the multidirectional patterns of hockey players. These results support the relationship between mobility and tibial diaphysis morphology as it is generally interpreted in the anthropological literature, with greater levels of mobility associated with increased diaphyseal robusticity and shape variation. Although exercise intensity may be the primary influence on these properties, the repetitiveness of the activity also deserves consideration. In conclusion, bone morphological patterns can reflect habitual behaviors, with adaptation to locomotor activities likely contributing to variation in tibial rigidity and shape properties in archaeological and fossil samples.

Ancient Ethiopian genome reveals extensive Eurasian admixture throughout the African continent

Ancient African helps to explain the present Tracing the migrations of anatomically modern humans has been complicated by human movements both out of and into Africa, especially in relatively recent history. Gallego Llorente et al. sequenced an Ethiopian individual, “Mota,” who lived approximately 4500 years ago, predating one such wave of individuals into Africa from Eurasia. The genetic information from Mota suggests that present-day Sardinians were the likely source of the Eurasian backflow. Furthermore, 4 to 7% of most African genomes, including Yoruba and Mbuti Pygmies, originated from this Eurasian gene flow. Science, this issue p. 820 Analysis of the genome of an ancient Ethiopian helps us understand recent human movement into Africa. Characterizing genetic diversity in Africa is a crucial step for most analyses reconstructing the evolutionary history of anatomically modern humans. However, historic migrations from Eurasia into Africa have affected many contemporary populations, confounding inferences. Here, we present a 12.5× coverage ancient genome of an Ethiopian male (“Mota”) who lived approximately 4500 years ago. We use this genome to demonstrate that the Eurasian backflow into Africa came from a population closely related to Early Neolithic farmers, who had colonized Europe 4000 years earlier.

Twenty Thousand-Year-Old Huts at a Hunter-Gatherer Settlement in Eastern Jordan

Ten thousand years before Neolithic farmers settled in permanent villages, hunter-gatherer groups of the Epipalaeolithic period (c. 22–11,600 cal BP) inhabited much of southwest Asia. The latest Epipalaeolithic phase (Natufian) is well-known for the appearance of stone-built houses, complex site organization, a sedentary lifestyle and social complexity—precursors for a Neolithic way of life. In contrast, pre-Natufian sites are much less well known and generally considered as campsites for small groups of seasonally-mobile hunter-gatherers. Work at the Early and Middle Epipalaeolithic aggregation site of Kharaneh IV in eastern Jordan highlights that some of these earlier sites were large aggregation base camps not unlike those of the Natufian and contributes to ongoing debates on their duration of occupation. Here we discuss the excavation of two 20,000-year-old hut structures at Kharaneh IV that pre-date the renowned stone houses of the Natufian. Exceptionally dense and extensive occupational deposits exhibit repeated habitation over prolonged periods, and contain structural remains associated with exotic and potentially symbolic caches of objects (shell, red ochre, and burnt horn cores) that indicate substantial settlement of the site pre-dating the Natufian and outside of the Natufian homeland as currently understood.

Extreme mobility in the Late Pleistocene? Comparing limb biomechanics among fossil Homo, varsity athletes and Holocene foragers

Descriptions of Pleistocene activity patterns often derive from comparisons of long bone diaphyseal robusticity across contemporaneous fossilized hominins. The purpose of this study is to augment existing understanding of Pleistocene hominin mobility patterns by interpreting fossil variation through comparisons with a) living human athletes with known activity patterns, and b) Holocene foragers where descriptions of group-level activity patterns are available. Relative tibial rigidity (midshaft tibial rigidity (J)/midshaft humeral rigidity (J)) was compared amongst Levantine and European Neandertals, Levantine and Upper Palaeolithic Homo sapiens, Holocene foragers and living human athletes and controls. Cross-country runners exhibit significantly (p<0.05) greater relative tibial rigidity compared with swimmers, and higher values compared with controls. In contrast, swimmers displayed significantly (p<0.05) lower relative tibial rigidity than both runners and controls. While variation exists among all Holocene H. sapiens, highly terrestrially mobile Later Stone Age (LSA) southern Africans and cross-country runners display the highest relative tibial rigidity, while maritime Andaman Islanders and swimmers display the lowest, with controls falling between. All fossil hominins displayed relative tibial rigidity that exceeded, or was similar to, the highly terrestrially mobile Later Stone Age southern Africans and modern human cross-country runners. The more extreme skeletal structure of most Neandertals and Levantine H. sapiens, as well as the odd Upper Palaeolithic individual, appears to reflect adaptation to intense and/or highly repetitive lower limb (relative to upper limb) loading. This loading may have been associated with bipedal travel, and appears to have been more strenuous than that encountered by even university varsity runners, and Holocene foragers with hunting grounds 2000-3000 square miles in size. Skeletal variation among the athletes and foraging groups is consistent with known or inferred activity profiles, which support the position that the Pleistocene remains reflect adaptation to extremely active and mobile lives.

Trade-Offs in Relative Limb Length among Peruvian Children: Extending the Thrifty Phenotype Hypothesis to Limb Proportions

Background and Methods Both the concept of ‘brain-sparing’ growth and associations between relative lower limb length, childhood environment and adult disease risk are well established. Furthermore, tibia length is suggested to be particularly plastic under conditions of environmental stress. The mechanisms responsible are uncertain, but three hypotheses may be relevant. The ‘thrifty phenotype’ assumes that some components of growth are selectively sacrificed to preserve more critical outcomes, like the brain. The ‘distal blood flow’ hypothesis assumes that blood nutrients decline with distance from the heart, and hence may affect limbs in relation to basic body geometry. Temperature adaptation predicts a gradient of decreased size along the limbs reflecting decreasing tissue temperature/blood flow. We examined these questions by comparing the size of body segments among Peruvian children born and raised in differentially stressful environments. In a cross-sectional sample of children aged 6 months to 14 years (n = 447) we measured head circumference, head-trunk height, total upper and lower limb lengths, and zeugopod (ulna and tibia) and autopod (hand and foot) lengths. Results Highland children (exposed to greater stress) had significantly shorter limbs and zeugopod and autopod elements than lowland children, while differences in head-trunk height were smaller. Zeugopod elements appeared most sensitive to environmental conditions, as they were relatively shorter among highland children than their respective autopod elements. Discussion The results suggest that functional traits (hand, foot, and head) may be partially protected at the expense of the tibia and ulna. The results do not fit the predictions of the distal blood flow and temperature adaptation models as explanations for relative limb segment growth under stress conditions. Rather, our data support the extension of the thrifty phenotype hypothesis to limb growth, and suggest that certain elements of limb growth may be sacrificed under tough conditions to buffer more functional traits.

Re-examining heritability: genetics, life history and plasticity.

Human life-history traits (growth, maturation, nutritional status) are increasingly associated with risk of chronic degenerative disease. Twin studies suggest high heritability of such traits; however, although sophisticated approaches have identified genetic variation underlying a proportion of this heritability, studies also increasingly demonstrate significant plasticity, and many life-history traits are able to change by one standard deviation (SD) over 3-6 generations. Developments in our understanding of the contributions of genetics and plasticity to human life history are likely to improve understanding of the growing burden of chronic diseases. We argue that a life-history approach to understanding variation in the human phenotype must integrate these two risk components, and highlight the important contribution of plasticity to changes in disease prevalence.

The influence of body proportions on femoral and tibial midshaft shape in hunter‐gatherers

Variation in femoral and tibial diaphyseal shape is used as an indicator of adaptation to patterns of terrestrial mobility. Recent experimentation has implied that lower limb diaphyseal shape may be primarily influenced by lower limb length, and less so by mobility patterns. If valid, this would, at most, render previous interpretations of mobility patterns based on analyses of diaphyseal shape questionable, and, at least, require additional standardization that considers the influence of limb length. Although the consequences could be profound, this implication has yet to be directly tested. Additionally, the influence of body breadth on tibial shape (and to a lesser extent femoral shape) remains uncertain. Tibial and femoral cross-sectional midshaft shape measurements, taken from nine Pleistocene and Holocene skeletal populations, were compared against lower limb length, limb segment length, and bi-iliac breadth. Generally, limb length and limb segment length do not significantly influence femoral or tibial midshaft shape. After controlling for body mass greater bi-iliac breadth is associated with a relative mediolateral strengthening of the femoral midshaft, while the influence of a wider body shape (BIB/length) is associated with a relative M-L strengthening of the tibia and femur of males, and the tibia of females. We conclude that; (1) mechanical interpretations of lower limb diaphyseal shape are most parsimonious due to the lack of evidence for a consistent relationship between segment length and shape; however, (2) further work is required to investigate the influence of bi-iliac breadth on both femoral and tibial midshaft shape.

Digit Ratio (2D:4D) and Rowing Ergometer Performance in Males and Females

Fetal and adult testosterone may be vital in the establishment and maintenance of sex-dependent abilities associated with male physical competitiveness. It has been shown that digit ratio (2D:4D) is negatively associated with prenatal testosterone, and it is also negatively associated with ability in sports such as football, skiing, middle distance running, and endurance running, which are dependent upon an efficient cardiovascular system. The relationship between digit ratio and sports requiring high power (physical strength) output in addition to well-developed cardiovascular systems has not been defined. This study investigated this association in male and female young adult rowers. Participants (77 male and 70 female) were student rowers encompassing a range of abilities from the University of Cambridge. Bilateral digit measurements were taken blind from each subject using Mitutoyo vernier calipers. Rowing performance over 2,000 m was assessed using the Concept 2 rowing ergometer. Significant negative correlations were observed between 2,000 m ergometer performance and male digit ratios, which persisted following adjustment for rowing experience and height. However, no such significant association was found in females despite a comparable sample size. Our data indicate that digit ratio is a predictor of ability in rowing, a sport which requires both cardiovascular efficiency and high power output, in males but not females. This in turn suggests that fetal testosterone exposure has long-term effects on traits associated with physical power in males but not females, suggesting a sex-difference in the capacity to respond to such exposures.

The Pre-Natufian Epipaleolithic: Long-term Behavioral Trends in the Levant

Few cultural developments have taken on as much archeological significance as when people began living in villages and producing their own food. The economic, social, technological, and ideological transformations immediately preceding and following these changes were profound. Early models of culture change associated with pre‐agricultural societies of the Levant focused on the sudden, late origin of settled farming villages triggered by climate change. Accompanying this new economic and living situation was durable stone‐built architecture; intensified plant and animal use; a flourishing of art and decoration; new mortuary traditions, including marked graves and cemeteries; elaborate ritual and symbolic behavior—a new way of life. This new life style arguably had a slow start, but really took off during the Epipaleolithic period (EP), spanning more than 10,000 years of Levantine prehistory from c. 23,000‐11,500 cal BP. The last EP phase, immediately preceding the Neolithic, is by far the best‐studied in terms of its cultural and economic contributions to questions on the origins of agriculture. 1–4 Recently, archeologists have considered the earlier parts of the EP to be more culturally dynamic and similar to the later phase (Natufian) than was previously thought. 3–10 The earlier EP is increasingly seen as demonstrating the behavioral variability and innovations that help us to understand the economic, technological, and social changes associated with complex hunter‐gatherers of the Natufian and farmers of the Neolithic. This paper traces the cultural and biological developments of the EP period leading up to the Natufian and considers the long‐term trajectory of culture change, social complexity, and village life in the Near East.