Testosterone-related abstracts from AAPA 2016

Facial width-to-height ratio (fWHR) is not associated with pubertal testosterone

Several researchers have proposed that facial width-to-height ratio (fWHR) is a sexually dimorphic signal that develops under the influence of pubertal testosterone (T); however, this hypothesis is currently under supported. Here we examine the association between fWHR and T during the period of the life span when facial growth is canalized--adolescence. To do so, we examine the association between T, known T-derived traits (i.e. strength and voice pitch), and craniofacial measurements in a sample of adolescent Tsimane males. If fWHR variation derives from pubertal T’s influence on craniofacial growth, several predictions can be made: 1) fWHR should increase with age as T increases, 2) fWHR should reflect adolescent T (rather than adult T per se), 3) fWHR should exhibit a growth spurt in parallel with T, 4) fWHR and T should correlate after controlling for potential confounds, and 5) fWHR should show a strong relationship to other T-derived traits. These effects were not observed. We also examined three additional facial masculinity ratios: facial width/lower face height, cheekbone prominence, and facial width/full face height. In contrast to fWHR, each of the three additional measures exhibit a strong age-related pattern of change and are associated with both T and T-dependent traits. In summary, our results challenge the status of fWHR as a sexually-selected signal of pubertal T and T-linked traits.

The relationship between social status, body size, and salivary hormone levels among Garisakang forager-horticulturalist men of lowland Papua New Guinea

Social hierarchy is a robust phenomenon that exists within all human societies. Over the past several decades, a growing body of evidence from industrialized Western populations has suggested that social status is closely related to individual measures of stress, health, and many other fitness-related traits. Data regarding such relationships, however, remain rare among small-scale subsistence societies, preventing a clear understanding of the importance of social position for fitness cross-culturally. Here we contribute to this area of research by exploring the relationship between adult male social status, BMI, and levels of salivary testosterone and diurnal cortisol among Garisakang small-scale forager-horticulturalists of lowland Papua New Guinea (N = 32). Three measures of individual social status – Respect, Dominance and Prosociality – were extracted from principal components analysis of photo-rank data for locally valued male traits (e.g., sociability, hunting ability, community influence). Preliminary results from multiple regression models controlling for age suggest complex relationships between social status, body size, and salivary hormone levels among the Garisakang. Male Dominance is positively related to BMI (p < 0.05) but not with salivary hormone measures, while greater male Respect is associated with reduced salivary cortisol (p = 0.06) but not testosterone or BMI. Prosociality, conversely, is not significantly related to any evaluated measure. We discuss the evolutionary implications of our findings, with a focus on future directions for investigating the biocultural interface of health in this population.

Men’s reproductive ecology and diminished hormonal regulation of skeletal muscle phenotype: An analysis of between- and within-individual variation among rural Polish men

Human life history is characterized by several distinctive features—sexual division of labor, prolonged care of altricial young, multiple dependents of different ages, and male provisioning. Testosterone has been suggested to mediate a trade-off between men’s reproduction and survival, through the regulation of sexually dimorphic musculature. This hypothesis predicts a relationship between testosterone and musculature in which mating effort, elevated testosterone, and dimorphic musculature covary positively. Testosterone is also posited to mediate a trade-off between mating and parenting effort, and accordingly, investing fathers show decreased testosterone production. Because men use their musculature not only in mating competition but also to support work demands, an important component of parenting effort, a relatively fixed relationship between testosterone and muscularity would seem maladaptive. We hypothesize that men’s parenting effort, specifically provisioning and subsistence activities, becomes a primary determinant of muscularity. Life history, anthropometric, and hormonal data were collected from 122 rural Polish men (at the Mogielica Human Ecology Study Site) during the summer harvest and for 103 of these participants in the winter. We found that fatherhood jointly predicted heavier workload and decreased testosterone, but positively predicted muscle mass and strength measures. Furthermore, within-individuals, men experienced intensified workload and suppressed testosterone during summer, along with a concomitant increase in muscularity and strength. These findings provide preliminary support for our model, termed the ‘Paternal Provisioning Hypothesis’. Between and within individuals, men’s provisioning and subsistence activities were robust predictors of muscular development and performance, whereas their testosterone levels had no appreciable effect on skeletal muscle phenotype.

Testosterone, musculature, and development in Kanyawara chimpanzees and Tsimane forager-horticulturalists

Considerable evidence suggests that the steroid hormone testosterone mediates major life-history trade-offs in primates, promoting mating effort at the expense of parenting effort or survival. In many species, chronic shifts in testosterone production over the life course correlate with investment in male-male competition. Chimpanzees and humans represent interesting test cases, because although closely related, they maintain divergent mating systems. Chimpanzee males do not invest in pair bonds or paternal care. Consequently, across the lifespan, their testosterone levels are expected to track changes in (1) behavioral investment in dominance striving, and (2) investment in sexually dimorphic musculature employed in male-male competition. Humans, by contrast, are expected to show weaker associations between testosterone and musculature, because the latter is important not only for male competition, but for men’s work provisioning wives and children. We assayed >7000 chimpanzee and >3350 Tsimane urine samples for testosterone, creatinine, and specific gravity, in the same laboratory using the same assay methods. Male chimpanzees showed peak acceleration in testosterone increase at age 6, peak velocity at age 10, and peak deceleration at age 14, reaching adult levels by 15-16, when they began to challenge other adult males. Adult levels of testosterone were achieved 3 years later than in captivity, likely reflecting energetic constraints in the wild. Indirect measures of muscle mass followed a similar pattern, and were highly correlated with testosterone. As predicted, Tsimane men exhibited a weaker correlation, with testosterone accounting for half as much variance in the muscle mass measure as in the chimpanzee sample.

Dads and cads? Male reproductive success, androgen profiles, and male-infant social bonds in wild mountain gorillas (Gorilla beringei beringei)

Male reproductive strategies are often reduced to a ‘dad versus cad’ dichotomy. When paternity certainty is high and mating opportunities scarce, theory predicts high levels of paternal investment; if paternity certainty is low and/or access to mating opportunities plentiful, male parenting is expected to be scarce. However, conflict between mating and parenting behavior is not equally strong across ecologies and social structures. Wild mountain gorillas (Gorilla beringei) have variable paternity certainty and a morphology suggestive of intense male contest competition. Despite this, relationships between males and infants are an important component of group structure, likely because males protect infants from infanticide and predation. Using data from gorilla groups monitored by the Dian Fossey Gorilla Fund’s Karisoke Research Center, we evaluated 1) the relationship between male-infant social bond strength and males’ reproductive success, and 2) the relationship between male-infant social bonds and males’ fecal androgen metabolite levels. Higher testosterone levels are generally correlated with increased aggression and mating activity, which are typically considered incompatible with parenting behavior. After controlling for male age and rank, males who had the strongest social bonds with infants were also the males with the highest reproductive success. There was no relationship between strength of male-infant social bonds and fecal androgen metabolite levels. Results demonstrate that reductive descriptions of male reproductive strategies may obscure important connections between mating and parenting effort, and highlight the need for additional data on the relationship between androgen activity, mating, and parenting in multimale/multifemale social systems.

Population genetic differentiation of height and body mass index across Europe

From Visscher and colleagues:

Population genetic differentiation of height and body mass index across Europe

Across-nation differences in the mean values for complex traits are common1, 2, 3, 4, 5, 6, 7, 8, but the reasons for these differences are unknown. Here we find that many independent loci contribute to population genetic differences in height and body mass index (BMI) in 9,416 individuals across 14 European countries. Using discovery data on over 250,000 individuals and unbiased effect size estimates from 17,500 sibling pairs, we estimate that 24% (95% credible interval (CI) = 9%, 41%) and 8% (95% CI = 4%, 16%) of the captured additive genetic variance for height and BMI, respectively, reflect population genetic differences. Population genetic divergence differed significantly from that in a null model (height, P < 3.94 × 10−8; BMI, P < 5.95 × 10−4), and we find an among-population genetic correlation for tall and slender individuals (r = −0.80, 95% CI = −0.95, −0.60), consistent with correlated selection for both phenotypes. Observed differences in height among populations reflected the predicted genetic means (r = 0.51; P < 0.001), but environmental differences across Europe masked genetic differentiation for BMI (P < 0.58).

NW-SE cline of brain volume in Europe

The authors of Modeling the 3D Geometry of the Cortical Surface with Genetic Ancestry mention:

In our group’s previous study, we found that area measures of cortical surface and total brain volumes of individuals of European descent in the United States correlate significantly with their ancestral geographic locations in Europe [ 9 ].

This 2011 study ("A Geographic Cline of Skull and Brain Morphology among Individuals of European Ancestry") is freely accessible:

Background: Human skull and brain morphology are strongly influenced by genetic factors, and skull size and shape vary worldwide. However, the relationship between specific brain morphology and genetically-determined ancestry is largely unknown. Methods: We used two independent data sets to characterize variation in skull and brain morphology among individuals of European ancestry. The first data set is a historical sample of 1,170 male skulls with 37 shape measurements drawn from 27 European populations. The second data set includes 626 North American individuals of European ancestry participating in the Alzheimer’s Disease Neuroimaging Initiative (ADNI) with magnetic resonance imaging, height and weight, neurological diagnosis, and genome-wide single nucleotide polymorphism (SNP) data. Results: We found that both skull and brain morphological variation exhibit a population-genetic fingerprint among individuals of European ancestry. This fingerprint shows a Northwest to Southeast gradient, is independent of body size, and involves frontotemporal cortical regions. Conclusion: Our findings are consistent with prior evidence for gene flow in Europe due to historical population movements and indicate that genetic background should be considered in studies seeking to identify genes involved in human cortical development and neuropsychiatric disease. [. . .]

Apparently the two main groups being compared in the neuroimaging sample are Americans of Northwestern European ancestry and Ashkenazi Jews ("ADNI subjects are spread out primarily along a NW-SE axis and form two distinct clusters corresponding to NW European and Ashkenazi Jewish ancestry"):

To determine if brain morphometry exhibits similar geospatial population trends to the skull morphometry data, we estimated the ancestry of each individual in the ADNI sample using available genome-wide genotype data and confined attention to 626 individuals with a high probability of having European ancestry. In order to assign the European region of origin most likely to reflect the genetic background of each individual, genotypes from ADNI subjects were merged with publically available genotypes from 34 reference populations geographically distributed across Europe, and PCA was pursued. [. . .]

A plot of the first two principal components separates ADNI subjects into two main clusters: one overlaps NW populations and one lies SE of Europe ( fig. 3 a) and overlaps individuals with self-reported Ashkenazi Jewish ancestry (online suppl. fig. S5). [. . .]

We found that ADNI individuals with a NW ancestry are on average 4 cm taller than ADNI individuals with a SE or Ashkenazi Jewish ancestry (p = 7.3 ! 10–6 ), consistent with previously observed differences in height across Europe [30] . [. . .]

Intracranial and brain volumes and cortical surface area progressively increase with the amount of inferred NW European ancestry (fig. ​(fig.3b),3b), and these measures are approximately 5% larger in the 10% of individuals with the most NW European ancestry compared to the 10% with the most SE European ancestry. This percentage increase matches the percentage increase in cranial length and breadth observed along the same NW-SE geographic axis in the skull data set (fig. ​(fig.2b)2b) and cannot be attributed to a correlation with body size since we controlled for height and weight. This correlation involves specific – not global – brain morphology because hippocampal, basal ganglia, ventricular, and cerebellar volumes and average cortical thickness are not associated with NW-SE ancestry.

Next, we performed both a region of interest analysis and vertex-based tests across the cortex to test whether the surface area of specific cortical regions showed more significant association with the degree of NW-SE ancestry. We found that cortical surface area predominantly in the frontal and temporal lobes from both hemispheres is significantly associated (online suppl. table S4) and is 4–9% larger among 10% of individuals with the most NW European ancestry compared to 10% with the most SE European ancestry. We found a similar frontotemporal pattern of association with the degree of NW-SE ancestry with a vertex-based analysis (fig. ​(fig.4;4; online suppl. fig. S6).

[. . .] the existence of genetic and craniometric clines in modern European populations suggests at least two theories: (1) pre-historic population movements made such a dominant contribution to the structure of genetic variation in Europe that more recent gene flow has not masked it, and (2) local environmental factors and selection generated clinal variation or acted to restore clinal variation after gene flow occurred. One intriguing possibility for such an environmental factor is the cultural conditions associated with possessing agricultural technologies, e.g. sedentarism, altered diet including milk consumption [40] , and new disease exposures [41] . As these technologies spread progressively from SE to NW Europe over several 1,000 years [33] , natural selection may have acted either directly or indirectly to alter brain morphology, thus creating the clinal variation found in this study.

Plots of cranial measures from this study (left) and map of head size from Coon's 1939 book The Races of Europe (right):

The trend observed here is also consistent with that reported by Maurice Fishberg over a century ago in The Jews: A Study of Race and Environment:

One of the methods of determining the volume of the brain case, and approximately the weight of the brain, is the determination of the cranial capacity. Very few direct measurements of this kind have been taken, because only few Jewish skulls have found their way into anthropological museums, where they could be studied carefully. But from the few studies of this character that have been made, it appears that the Jews are somewhat at a disadvantage. Lombroso's studies of the Jews in Turin, Italy, which were made in an indirect fashion, showed that the Jews have a smaller cranial capacity than the Catholics of that city.2 Weinberg collected measurements of seventeen Jewish skulls in various museums of Europe, which were made properly, and are not approximations. The average cranial capacity was 1421 c.cm., which is about thirty to forty c.cm. below the average cranial capacity of the population of Europe. Of course the small number of skulls thus measured is not sufficient to draw positive conclusions.

As to the weight of the brain, there are also very few observations on record. The author knows only of twentythree Jewish brains reported by Giltchenko,3 four by Weisbach,4 and three by Weinberg.5 The average weight of these brains, as calculated by Weinberg, was 1320.4 gm. Since the average weight of the brain of the European is 1350 gms., the brain of Jews is rather lighter by 30 gms. , or nearly one ounce. Considering that the Jews are shorter of stature than the average Europeans, it would be expected that their brain should also be smaller. But, as Weinberg points out, the average for Germans was found to be 8.22 gm. of brain tissue for each centimetre of stature, while for the Jews it is only 8.05 gms. This shows the Jewish brain lighter not only absolutely, but also relatively.

Racial differences in brain shape

A press release:

Researchers at the University of California, San Diego and the School of Medicine have found that the three-dimensional shape of the cerebral cortex -- the wrinkled outer layer of the brain controlling many functions of thinking and sensation -- strongly correlates with ancestral background.

Modeling the 3D Geometry of the Cortical Surface with Genetic Ancestry

Knowing how the human brain is shaped by migration and admixture is a critical step in studying human evolution [ 1, 2 ], as well as in preventing the bias of hidden population structure in brain research [ 3, 4 ]. [. . .] The geometry of the cortical surface contains richer information about ancestry than the areal variability of the cortical surface, independent of total brain volumes. Besides explaining more ancestry variance than other brain imaging measurements, the 3D geometry of the cortical surface further characterizes distinct regional patterns in the folding and gyrification of the human brain associated with each ancestral lineage.

The ancestry and affiliations of Kennewick Man

Kennewick Man ancient DNA. The paper is openly accessible. Results pretty much as I expected.

We find that Kennewick Man is closer to modern Native Americans than to any other population worldwide.

The paper is marred by strained, politically-motivated attempts to tie Kennewick Man specifically to "the Confederated Tribes of the Colville Reservation (Colville), one of the five tribes claiming Kennewick Man". So those interested in aboriginal American population structure are probably better off ignoring much of the authors's narrative and looking directly at the data.

Variation and signatures of selection on the human face

Variation and signatures of selection on the human face. [Open access]

J Hum Evol. 2014 Oct;75:143-52

Authors: Guo J, Tan J, Yang Y, Zhou H, Hu S, Hashan A, Bahaxar N, Xu S, Weaver TD, Jin L, Stoneking M, Tang K

Abstract

There has been much debate about why humans throughout the world differ in facial form. Previous studies of human skull morphology found levels of among-population differentiation that were comparable to those of neutral genetic markers, suggesting that genetic drift (neutral processes) played an important role in influencing facial differentiation. However, variation in soft-tissue morphology has not been studied in detail. In this study, we analyzed high-resolution 3D images of soft-tissue facial form in four Eurasian populations: Han Chinese, Tibetans, Uyghur and Europeans. A novel method was used to establish a high-density alignment across all of the faces, allowing facial diversity to be examined at an unprecedented resolution. These data exhibit signatures of population structure and history. However, among-population differentiation was higher for soft-tissue facial form than for genome-wide genetic loci, and high-resolution analyses reveal that the nose, brow area and cheekbones exhibit particularly strong signals of differentiation (Qst estimates: 0.3-0.8) between Europeans and Han Chinese. Our results suggest that local adaptation and/or sexual selection have been important in shaping human soft-tissue facial morphology. [. . .]

The Qpc values found in the nose and brow area between Europeans and Han Chinese approach the high differentiation reported for skin pigmentation (Relethford, 2004b). This suggests that strong local adaptation may have shaped these facial features (Myles et al., 2007). For the nose, strong correlations have been found between the nasal index and temperature/humidity, supporting climate adaptation as the major selective force (Thomson and Buxton, 1923, Davies, 1932, Weiner, 1954, Wolpoff, 1968, Hiernaux and Froment, 1976, Crognier, 1981 and Franciscus and Long, 1991). Models simulating airflow dynamics demonstrated that bigger nasal volumes, narrower shapes and downwardly pointing nares might enhance the airflow exposure of the mucosa and thereby facilitate the heating and humidification of the air (Churchill et al., 2004). The European nose shape thus may have resulted from adaptation to a colder climate. The relatively enlarged brow area in Europeans has also been noted previously (Russell et al., 1985). It has been argued that brow area size is positively correlated with the magnitude of the mechanical stresses resulting from mastication, so brow area shape differentiation (SOM, Fig. S11) could be the result of dietary differences (Russell et al., 1985). Adaptation to specific diets (Hubbe et al., 2009) and climate adaptation (Coon et al., 1950) have been hypothesized to explain the expanded zygomatics in Asians.

In addition to natural selection, sexual selection may also have played a major role in shaping interpopulation variation in the human face. Selective mate choice based on facial appearance in humans is well documented as a universal condition in global populations (Wells et al., 2009). However, whether and to what extent sexual selection shaped human facial morphology has rarely been investigated. Fisher's runaway sexual selection model suggests that a positive feedback loop composed of an arbitrary trait involving appearance, and the accidental preference of this trait in the opposite sex, could initiate a powerful sexual selection process (Fisher, 1958). It is therefore possible that some of the strong differentiation signals involving the soft-tissue facial form may have resulted from sexual selection. Further studies that combine high-resolution 3D face analysis, studies of human behavior, and genetic analyses are necessary to delineate the possible roles of local adaptation versus sexual selection in explaining the relatively large between-population differentiation that we find for soft-tissues of the human face.

"Monkeys' faces evolved to avoid crossbreeding"

BBC: Guenon monkeys' colourful and varied faces have evolved as a way to avoid crossbreeding, scientists have found.

Dr James Higham, senior author, said: "Evolution produces adaptations that help animals thrive in a particular environment, and over time these adaptations lead to the evolution of new species.

"A key question is what mechanisms keep closely related species that overlap geographically from interbreeding, so that they are maintained as separate species.

"Our findings offer evidence for the use of visual signals to help ensure species recognition: species may evolve to look distinct specifically from the other species they are at risk of interbreeding with," Dr Higham said.

"In other words, how you end up looking is a function of how those around you look. With the primates we studied, this has a purpose: to strengthen reproductive isolation between populations."

Interesting-looking AAPA 2013 abstracts

Program here (pdf).

Natural selection acts to maintain diversity between Out of Africa and sub-Saharan African populations in genes related to neurological processes and brain development. JASON A. HODGSON1,5, ALI AL-MEERI2, CONNIE J. MULLIGAN3 and RYAN L. RAAUM4,5. 1Anthropology, New York University, 2Biochemistry and Molecular Biology, Sana'a University, Yemen, 3Anthropology, University of Florida, 4Anthropology, Lehman College and The Graduate Center CUNY, 5-, The New York Consortium in Evolutionary Primatology.

The Yemeni and Mozabite are closely related Out of Africa (OOA) populations from the Arabian Peninsula and North Africa respectively, while the Maasai are a sub-Saharan African (SSA) population. Using genome-wide SNP data (publicly available for the Mozabite and Maasai, and collected here for the Yemeni) we show the Yemeni to have ~7% and the Mozabite to have ~26% recent sub-Saharan admixture, while the Maasai have ~27% Middle Eastern admixture. We use an adaptation of the locus specific branch length method to look for the effects of natural selection on alleles introduced to the three populations through admixture. We specifically look for 1) the adaptive introgression of alleles from SSA into the Yemeni and Mozabite, 2) the adaptive introgression of alleles from OOA into the Maasai, 3) purifying selection of SSA alleles out of the Yemeni and Mozabite, and 4) purifying selection of OOA alleles out of the Maasai. We found correspondence in patterns of adaptive introgression and purifying selection between the populations for 18 genomic loci, all of which contain protein-coding genes. The correspondence in signatures of selection between three independent populations is strong evidence for natural selection, rather than the false positive signals common in genome-wide scans of selection. Strikingly, of the regions where purifying selection is acting to maintain diversity between the Out of Africa and sub-Saharan African populations, eight out of twelve genes with known ontologies are involved in neurological processes or brain development. A binomial test found this enrichment to be significant. This research was partially supported by NSF grant BCS-0518530.

Protective buttressing of the human fist and the evolution of hominin hands

FIGHTING SHAPED HUMAN HANDS. Protective buttressing of the human fist and the evolution of hominin hands

The derived proportions of the human hand may provide supportive buttressing that protects the hand from injury when striking with a fist. Flexion of digits 2–5 results in buttressing of the pads of the distal phalanges against the central palm and the palmar pads of the proximal phalanges. Additionally, adduction of the thenar eminence to abut the dorsal surface of the distal phalanges of digits 2 and 3 locks these digits into a solid configuration that may allow a transfer of energy through the thenar eminence to the wrist. To test the hypothesis of a performance advantage, we measured: (1) the forces and rate of change of acceleration (jerk) from maximum effort strikes of subjects striking with a fist and an open hand; (2) the static stiffness of the second metacarpo-phalangeal (MCP) joint in buttressed and unbuttressed fist postures; and (3) static force transfer from digits 2 and 3 to digit 1 also in buttressed and unbuttressed fist postures. We found that peak forces, force impulses and peak jerk did not differ between the closed fist and open palm strikes. However, the structure of the human fist provides buttressing that increases the stiffness of the second MCP joint by fourfold and, as a result of force transfer through the thenar eminence, more than doubles the ability of the proximal phalanges to transmit ‘punching’ force. Thus, the proportions of the human hand provide a performance advantage when striking with a fist. We propose that the derived proportions of hominin hands reflect, in part, sexual selection to improve fighting performance.

Human hands have 'evolved for fighting'

Compared with apes, humans have shorter palms and fingers and longer, stronger flexible thumbs.

Experts have long assumed these features evolved to help our ancestors make and use tools.

But new evidence from the US suggests it was not just dexterity that shaped the human hand, but violence also.

Hands largely evolved through natural selection to form a punching fist, it is claimed.

''The role aggression has played in our evolution has not been adequately appreciated,'' said Professor David Carrier, from the University of Utah.

''There are people who do not like this idea but it is clear that compared with other mammals, great apes are a relatively aggressive group with lots of fighting and violence, and that includes us. We're the poster children for violence.'' [. . .]

''Individuals who could strike with a clenched fish could hit harder without injuring themselves, so they were better able to fight for mates and thus be more likely to reproduce,'' he said. [. . .]

To test the theory Prof Carrier conducted experiments with volunteers aged 22 to 50 who had boxing or martial arts experience.

In one, participants were asked to hit a punchbag as hard as possible from different directions with their hands in a range of shapes, from open palms to closed fists.

The results, published in the Journal of Experimental Biology, show that tightly clenched fists are much more efficient weapons than open or loosely curled hands.

A punch delivers up for three times more force to the same amount of surface area as a slap. And the buttressing provided by a clenched fist increases the stiffness of the knuckles fourfold, while doubling the ability of the fingers to deliver a punching force. [. . .]

''Human-like hand proportions appear in the fossil record at the same time our ancestors started walking upright four million to five million years ago. An alternative possible explanation is that we stood up on two legs and evolved these hand proportions to beat each other.''

Manual dexterity could have evolved without the fingers and palms getting shorter, he said. But he added: ''There is only one way you can have a buttressed, clenched fist: the palms and fingers got shorter at the same time the thumb got longer.''

Prof Carrier cited other evidence pointing to the role of fighting in the evolution of human hands.

:: No ape other than humans hits with a clenched fist.

:: Humans use fists instinctively as threat displays. ''If you are angry, the reflexive response is to form a fist,'' said Prof Carrier. ''If you want to intimidate somebody, you wave your fist.''

:: Sexual dimorphism, or the difference in body size between the sexes, tends to be greater among primates when there is more competition between males. In humans the difference is mainly in the upper body and arms, especially the hands. ''It's consistent with the hand being a weapon,'' said Prof Carrier.

In their paper the professor and colleague Michael Morgan, a University of Utah medical student, ponder on the paradoxical nature of the human hand.

''It is arguably our most important anatomical weapon, used to threaten, beat and sometimes kill to resolve conflict. Yet it is also the part of our musculoskeletal system that crafts and uses delicate tools, plays musical instruments, produces art, conveys complex intentions and emotions, and nurtures,'' they write.

''More than any other part of our anatomy, the hand represents the identity of Homo sapiens. Ultimately, the evolutionary significance of the human hand may lie in its remarkable ability to serve two seemingly incompatible but intrinsically human functions.''

Kennewick Man update

Kennewick Man bones not from Columbia Valley, scientist tells tribes

The skeleton, more than 9,500 years old, has long been at the center of a rift between tribal members and scientists, led by Doug Owsley, a physical anthropologist at the Smithsonian Institution's National Museum of Natural History who spearheaded the legal challenge to gain access to the skeleton for scientific study.

Owsley says study shows that not only wasn't Kennewick Man Indian, he wasn't even from the Columbia Valley, which was inhabited by prehistoric Plateau tribes. [. . .]

Isotopes in the bones told scientists Kennewick Man was a hunter of marine mammals, such as seals, Owsley said. "They are not what you would expect for someone from the Columbia Valley," he said. "You would have to eat salmon 24 hours a day and you would not reach these values.

"This is a man from the coast, not a man from here. I think he is a coastal man." [. . .]

Pressed by Armand Minthorn of the Umatilla Board of Trustees, who asked Owsley directly, "Is Kennewick Man Native American?" Owsley said no. "There is not any clear genetic relationship to Native American peoples," Owsley said. "I do not look at him as Native American ... I can't see any kind of continuity. He is a representative of a very different people."

His skull, Owsley said, was most similar to an Asian Coastal people whose characteristics are shared with people, later, of Polynesian descent.

And, while tribes want the remains returned for reburial, Owsley said there is still much more to learn from the skeleton, which has largely been inaccessible but for two instances, in which a team of about 15 scientists could study it for a total of about two weeks.

Note: my own understanding is that Kennewick Man is broadly similar to other Paleoindians, and that historical Amerindians probably derive most of their ancestry from Paleoindians (with some later Asian gene flow and evolution in a more Mongoloid direction). On the other hand, it appears W. Eurasian-affiliated ancient Central Asians did contribute significantly to the ancestry of Paleoindians (and, to a lesser extent, to the ancestry of modern E. Eurasians in general), which is what I expect most of the heightened affinity between Northern Europeans and Amerindians found by Reich et al. is attributable to.

Selection for height in Northern Europeans

Evidence of widespread selection on standing variation in Europe at height-associated SNPs:

Strong signatures of positive selection at newly arising genetic variants are well documented in humans1, 2, 3, 4, 5, 6, 7, 8, but this form of selection may not be widespread in recent human evolution9. Because many human traits are highly polygenic and partly determined by common, ancient genetic variation, an alternative model for rapid genetic adaptation has been proposed: weak selection acting on many pre-existing (standing) genetic variants, or polygenic adaptation10, 11, 12. By studying height, a classic polygenic trait, we demonstrate the first human signature of widespread selection on standing variation. We show that frequencies of alleles associated with increased height, both at known loci and genome wide, are systematically elevated in Northern Europeans compared with Southern Europeans (P < 4.3 × 10−4). This pattern mirrors intra-European height differences and is not confounded by ancestry or other ascertainment biases. The systematic frequency differences are consistent with the presence of widespread weak selection (selection coefficients ~10−3–10−5 per allele) rather than genetic drift alone (P < 10−15).

Luke Jostins described this research last year:

Europeans differ systematically in their height, and these differences correlate with latitude. The average Italian is 171cm, whereas the average Swede is a full 4cm taller. Are these differences genetic? Have they been under evolutionary selection in recent human history?

Michael Turchin gave some pretty convincing answers to these questions, using genetic data from the 129 thousand individuals in the GIANT consortium. He compared the frequencies of alleles that are known to increase height, and found that they are more common in Northern Europe. Interestingly, he found the same relationship for alleles that have weaker evidence for height association, showing that there are still a large number of common height variants hiding in the genome, which are also more frequent in Northern Europe.

Height differences are thus heritable, but have they been under evolutionary selection? Or are these differences merely down to genetic drift? This can also be tested using the GIANT data, which shows significant statistical evidence of selection on height variants in recent history. On top of that, the magnitude of the selection is correlated with the effect size of the height variant, providing strong evidence that these variants are being selected specifically for their impact on height.

This is a textbook example of how an evolutionary study should be done; you show a phenotypic difference exists, that it is heritable, and that it is under selection. This opens the question as to why height has been selected in Northern Europe (or shortness in Southern Europe). Could the same data be used to test specific hypotheses there?

John Hawks intro physical anthropology course

Principles of Biological Anthropology. This has been up for a while, but apparently Hawks may be removing the videos in the near future, so watch soon if interested.

Hawks also has a teaching company course.

Dental morphological evidence for European admixture in Mongolia and western China

Lee, C. and Scott, G. R. (2011), Brief communication: Two-rooted lower Canines—A European trait and sensitive indicator of admixture across Eurasia. American Journal of Physical Anthropology, 146: 481–485. doi: 10.1002/ajpa.21585

With the exception of Carabelli's trait, the European dentition is better known for the morphological traits that it does not exhibit rather than the ones that it does. One root trait, however, runs counter to the characterization of reduced and simplified European crowns and roots. Although a rare trait in general, two-rooted lower canines are much more common in Europeans than in any other regional grouping and, given adequate sample sizes, can be useful in evaluating gene flow between Europeans and neighboring groups. In European samples, two-rooted lower canines consistently exhibit frequencies of 5–8%. In our sample from northern Spain, the trait attains a frequency of almost 10%. In contrast, in Sub-Saharan Africans the trait is virtually unknown while in Asian and Asian-derived populations, it varies between 0.0 and 1.0%. Here we show that two-rooted canine frequencies for new migrants along the western frontiers of China and Mongolia ranged from 0–4%. These data suggest European-derived populations migrated into western China (Xinjiang Province) and Mongolia (Bayan Olgii Aimag) sometime during the late Bronze age (1000–400 BCE). [. . .]

One of the major concerns of Alexandersen (1963) regarding two-rooted lower canines revolved around the issue of ‘‘atavism.’’ This term, rarely used today, begs the question of whether or not this double rooted form was common at one time, then disappeared, only to reappear sometime later. Swindler (1995) notes that ‘‘the deciduous and permanent canines in the majority of living primates have a single root.’’ This suggests that two-rooted lower canines are not the ancestral condition in anthropoids or hominoids. Rather, the phenotype is a derived condition, found primarily in recent human populations distributed across Western Eurasia.

The presence of the two-rooted canines in East Asia may provide some clue as to the eastward migration of new populations into China and Mongolia. The largest numbers of individuals with this trait are concentrated along the western and northern frontiers of China and Mongolia. Archaeological excavations support the large scale movement of people into this area during the Bronze age (ca. 2200 BCE–400 BCE). Burial artifacts and settlement patterns suggest cultural and technological ties to the Afanasevo culture in Siberia, which in turn is linked archaeologically, linguistically, and genetically with the Indo-European Tocharian populations that appear to have migrated to the Tarim Basin ca. 4,000 years ago (Ma and Sun, 1992; Ma and Wang, 1992; Mallory and Mair, 2000; Romgard, 2008; Keyser et al., 2009; Li et al., 2010).

The appearance of a new population on the western frontier also supports the findings of previous research in cranial metrics, dental nonmetrics, and DNA. Using cranial metrics and archaeological dating, Han (1994) hypothesized the earliest large-scale migration into western China occurred during the early Bronze age (2000 BCE) from Central Asia or southern Siberia. Dental nonmetric data also support multiple migrations into western China (Xinjiang Province) from Central Asia during the Bronze age to Iron age (Lee, 2007; Zhang, 2010). mtDNA studies on archaeological and modern population samples from Xinjiang Province show heterogeneous Asian and European genetic signatures dating from the Bronze age to the present (Yao et al., 2004; Cui et al., 2010; Zhang et al., 2010; Li et al., 2010).

As the frequency of two-rooted canines is highest in European samples and low to nonexistent in Asians, we propose this trait was introduced into East Asia by Indo- European speaking groups or their affines crossing the western frontier of China and Mongolia. Further data are needed to clarify aspects of these population movements, including the identity of the migrants, along with the number, routes, and timing of the migrations.

Although two-rooted lower canines cannot offer the precision of DNA in evaluating the ancestry in individual skulls, this trait is a sensitive indicator of admixture wherever Europeans come in contact with Asian or African populations. As this distinctive trait can be scored with relative ease in large samples, it provides a useful supplemental tool in discerning gene flow between distantly related populations going back many millennia.

Neolithic Y DNA from Southwestern France

A post by Dienekes brings to my attention a paper in PNAS, "Ancient DNA reveals male diffusion through the Neolithic Mediterranean route":

The Neolithic is a key period in the history of the European settlement. Although archaeological and present-day genetic data suggest several hypotheses regarding the human migration patterns at this period, validation of these hypotheses with the use of ancient genetic data has been limited. In this context, we studied DNA extracted from 53 individuals buried in a necropolis used by a French local community 5,000 y ago. The relatively good DNA preservation of the samples allowed us to obtain autosomal, Y-chromosomal, and/or mtDNA data for 29 of the 53 samples studied. From these datasets, we established close parental relationships within the necropolis and determined maternal and paternal lineages as well as the absence of an allele associated with lactase persistence, probably carried by Neolithic cultures of central Europe. Our study provides an integrative view of the genetic past in southern France at the end of the Neolithic period. Furthermore, the Y-haplotype lineages characterized and the study of their current repartition in European populations confirm a greater influence of the Mediterranean than the Central European route in the peopling of southern Europe during the Neolithic transition.

Note: contra the authors' assertion, lactase persistence was probably not carried by Neolithic central Europeans; the most common European LP-associated allele has been absent in all central European Neolithic samples tested to date.

Dienekes writes:

R-M269 which, because of its apparent young Y-STR age has been tied by some to either the Mediterranean or Central European Neolithic is conspicuous absently from both at the moment. It may yet surface in a Neolithic context, but its absence this late from a region where, today, it is abundant only adds to its mystery.

In fact, the amateur estimates using actual mutation rates put the spread of R1b into Western Europe clearly post-Neolithic.

R1b and LP in Western Europe are in all likelihood associated with the dispersal of Indo-European languages.

These findings add to ancient DNA evidence indicating large-scale post-Neolithic population replacement in Europe. Coon and other traditional physical anthropologists, it turns out, probably had a better handle on European prehistory 70 years ago than population geneticists did five years ago.

Craniometric data support a mosaic model of demic and cultural Neolithic diffusion to outlying regions of Europe

Full text is free:

The extent to which the transition to agriculture in Europe was the result of biological (demic) diffusion from the Near East or the adoption of farming practices by indigenous hunter–gatherers is subject to continuing debate. Thus far, archaeological study and the analysis of modern and ancient European DNA have yielded inconclusive results regarding these hypotheses. Here we test these ideas using an extensive craniometric dataset representing 30 hunter–gatherer and farming populations. Pairwise population craniometric distance was compared with temporally controlled geographical models representing evolutionary hypotheses of biological and cultural transmission. The results show that, following the physical dispersal of Near Eastern/Anatolian farmers into central Europe, two biological lineages were established with limited gene flow between them. Farming communities spread across Europe, while hunter–gatherer communities located in outlying geographical regions adopted some cultural elements from the farmers. Therefore, the transition to farming in Europe did not involve the complete replacement of indigenous hunter–gatherer populations despite significant gene flow from the Southwest Asia. This study suggests that a mosaic process of dispersal of farmers and their ideas was operating in outlying regions of Europe, thereby reconciling previously conflicting results obtained from genetic and archaeological studies.

Jean M comments:

Their results are remarkably neat, showing two clearly distinct lineages, with comparatively little inter-mixture, confirming the picture from the archaeology of the LBK, for example, which seems to indicate that farmers and foragers kept to their own zones.

This helps to explain why the presumed Neolithic Y-DNA haplogroups G, E and J do not dominate Europe today, and decline in frequency the further one moves from the Mediterranean. The farming pioneers in Europe, though initially successful, eventually encountered problems which led to population crashes. Then after the Neolithic, Europe had two great bursts of migration, both from fringe regions where farming had been adopted by foragers. One came from the European steppe in the Copper and Bronze Ages. The other was the spread of their Germanic and Slavic descendants in the Migration Period.

Further update on People of the British Isles project

From their most recent newsletter (pdf):

We are pleased to tell you that we have just submitted our first scientific paper about the project. The main function of this paper is to announce PoBI to the scientific world and in it we show that, even with a relatively small number of samples and a few genetic markers, the samples we collected should be sufficient to detect genetic differences across the UK. [. . .]

One aspect that is of particular interest is the surnames we collected and we have spent some time with our collaborators at UCL (Professor Paul Longley and his group) dividing them into local and non-local surnames. The figure on the left shows a couple of examples. The idea is that individuals whose surname is local to an area are more likely to have family in that area for many generations than individuals whose surnames are found all over the country. This is obviously a generalisation, but it does seem that there are some genetic differences between sets of volunteers with local surnames and sets with non-local surnames and we are really looking forward to analysing all the data rather than just the small subset we have been studying so far. [. . .]

Our next priority is to analyse the 1.3 million genetic markers that have been typed on 3,000 of our volunteers [. . .] The data we analyse from these samples should shed light on the genetic impact of the different historical incursions into Britain. It is an extremely large data set and so it will take a while to analyse and write up. As mentioned in our last newsletter, 100 of our samples are having their complete DNA sequenced by the 1,000 Genomes Project (www.1000genomes.org) and it should not be too long before that very valuable information becomes available to us. [. . .]

As you will know from the last newsletter, the Wellcome Trust has given us funding for a further five years to look for genes involved in normal traits. The main focus is on facial features, but other traits include handedness, taste perception and skin colour. We have been going back to our volunteers to collect these data. We take 3D photographs of each volunteer’s face in order to identify genes involved in the control of particular facial features. Over the last 18 months, we have collected 475 such photographs and are beginning to analyse them with our collaborators in Surrey (Professor Josef Kittler and his group).

Last newsletter (pdf):

There is a great deal of interest in the genetics of facial features and, in addition, the frequency of genetic variants for facial features may well differ significantly between different parts of the UK. We will also be collecting data on a variety of other normal features including height, hair and skin colour, handedness, milk tolerance, musical preferences and perfect pitch, taste and smell preferences and features of the hand.

Victor Mair talk on Tarim Basin Mummies

Part of a series of lectures related to the "Secrets of the Silk Road" exhibition at the University of Pennsylvania Museum of Archaeology and Anthropology. The mummy and artifacts abruptly pulled from the exhibition by the Chinese government before it opened are back for now.

Why does head form change in children of immigrants? A reappraisal.

More from Jantz on Boas:

CONCLUSIONS: The results support the two hypotheses tested. Change in Hebrew cranial indices resulted from abandoning the practice of cradling infants in America. U.S.-born Sicilian children experienced an environment worse than the one in Europe, and consequently experienced impaired growth. We conclude that the changes Boas observed resulted from specific behavioral and economic conditions unique to each group, rather than a homogeneous American environment.

Twenty-eleven

I'll skip the predictions (you're welcome to post your own), and just post a bit more information on a few projects that should be announcing results this year:

(1) Otzi genome. Here's a 9 minute podcast from Life Technologies containing a few more details:
- "above 5X coverage"
- "looking at potentially medically-relevant SNPs"
- "this individual living over 5000 years ago would represent an ancestor for, we think, a significant proportion of the European population."
- "looking at his ancestry and indeed trying to determine exactly where is he from"

(2) People of the British Isles Project. A movie from the Wellcome Trust:



Most interestingly, the project is now collecting phenotypic data, including skin color, and taking 3-d facial photographs. Bodmer: "The next stage of our study, we're now taking pictures of people's faces so we can analyze components statistically [. . .] and then look for the genetic features behind that. What are the genes, what are the variations that determine facial features. Will it be possible to reconstruct from a piece of DNA what a person really looked like."

(3) 1000 Genomes Project. Another short film by the Wellcome Trust:



Chris Tyler-Smith: "[The project has] told us that natural selection has influenced virtually every part of our genome [. . .] we've now got a catalog of some thousands of genes that we think have been specifically positively selected in our fairly recent history."

The Denisova hominin need not be an out of Africa story

I had a similar reaction when the original article was published, but this piece in the Journal of Human Evolution makes a much more extensive and better-argued case:

The recent retrieval of a complete mitochondrial (mt) DNA sequence from a 48–30 ka human bone from Denisova (Siberia) (Krause et al., 2010) is a remarkable achievement fully deserving international acclaim. Without wishing to detract from this feat, however, we wish to challenge their conclusion that the Denisova hominin “derives from a hominin migration out of Africa [ca. 1.0 Ma] distinct from that of the ancestors of Neanderthals and of modern humans” (Krause et al., 2010: 894). In addition, we challenge their assumption that the ancestors of the Neanderthals left Africa between 500–300 ka. In our view, alternative interpretations of the evidence are available and should be considered.

Longer excerpts below: