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Thursday, December 13, 2012

Sapiens

 

An early and enduring advanced technology originating 71,000 years ago in South Africa

Kyle Brown et al.
Nature, 22 November 2012, Pages 590-593

Abstract:
There is consensus that the modern human lineage appeared in Africa before 100,000 years ago. But there is debate as to when cultural and cognitive characteristics typical of modern humans first appeared, and the role that these had in the expansion of modern humans out of Africa. Scientists rely on symbolically specific proxies, such as artistic expression, to document the origins of complex cognition. Advanced technologies with elaborate chains of production are also proxies, as these often demand high-fidelity transmission and thus language. Some argue that advanced technologies in Africa appear and disappear and thus do not indicate complex cognition exclusive to early modern humans in Africa. The origins of composite tools and advanced projectile weapons figure prominently in modern human evolution research, and the latter have been argued to have been in the exclusive possession of modern humans. Here we describe a previously unrecognized advanced stone tool technology from Pinnacle Point Site 5-6 on the south coast of South Africa, originating approximately 71,000 years ago. This technology is dominated by the production of small bladelets (microliths) primarily from heat-treated stone. There is agreement that microlithic technology was used to create composite tool components as part of advanced projectile weapons. Microliths were common worldwide by the mid-Holocene epoch, but have a patchy pattern of first appearance that is rarely earlier than 40,000 years ago, and were thought to appear briefly between 65,000 and 60,000 years ago in South Africa and then disappear. Our research extends this record to ~71,000 years, shows that microlithic technology originated early in South Africa, evolved over a vast time span (~11,000 years), and was typically coupled to complex heat treatment that persisted for nearly 100,000 years. Advanced technologies in Africa were early and enduring; a small sample of excavated sites in Africa is the best explanation for any perceived ‘flickering' pattern.

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Network Science in Egyptology

Patrick Coulombe et al.
PLoS ONE, November 2012

Abstract:
Egyptology relies on traditional descriptive methods. Here we show that modern, Internet-based science and statistical methods can be applied to Egyptology. Two four-thousand-year-old sarcophagi in one tomb, one within the other, with skeletal remains of a woman, gave us the opportunity to diagnose a congenital nervous system disorder in the absence of a living nervous system. The sarcophagi were discovered near Thebes, Egypt. They were well preserved and meticulously restored. The skeletal remains suggested that the woman, aged between 50 and 60 years, was Black, possibly of Nubian descent and suffered from syringobulbia, a congenital cyst in the brain stem and upper spinal cord. We employed crowd sourcing, the anonymous responses of 204 Facebook users who performed a matching task of living persons' iris color with iris color of the Udjat eyes, a decoration found on Egyptian sarcophagi, to confirm the ethnicities of the sarcophagus occupants. We used modern fMRI techniques to illustrate the putative extent of her lesion in the brain stem and upper spinal cord deduced from her skeletal remains. We compared, statistically, the right/left ratios, a non-dimensional number, of the orbit height, orbit width, malar height and the infraorbital foramena with the same measures obtained from 32 ancient skulls excavated from the Fayum, North of Thebes. We found that these ratios were significantly different in this skull indicating atrophy of cranial bones on the left. In this instance, Internet science and the use of modern neurologic research tools showed that ancient sarcophagus makers shaped and decorated their wares to fit the ethnicity of the prospective occupants of the sarcophagi. We also showed that, occasionally, human nervous system disease may be recognizable in the absence of a living nervous system.

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Rushton's r-K life history theory of race differences in penis length and circumference examined in 113 populations

Richard Lynn
Personality and Individual Differences, forthcoming

"Rushton (1985, 2000) has advanced a theory of race differences in r-K life history. The theory is drawn from biology, in which species are categorized on a continuum running from r strategists to K strategists; r strategists have large numbers of offspring and invest relatively little in them, while K strategists have fewer offspring and invest heavily in them by feeding and protecting them during infancy and until they are old enough to look after themselves (Wilson, 1975)...Rushton (2000) has applied r-K life history theory to the three major races of Homo sapiens: Mongoloids (East Asians), Caucasoids (Europeans, South Asians and North Africans), and Negroids (sub-Saharan Africans). His theory is that East Asians are the most K evolved and Negroids the least K evolved, while Caucasoids fall intermediate between the two although closer to East Asians. Rushton has supported his theory by documenting that the three races differ in brain size, intelligence, length of gestation, rate of maturation in infancy and childhood, and a number of other variables including penis length and diameter. Rushton (2000, pp. 167-169) reports that penis length and diameter are greatest in Negroids, intermediate in Caucasoids and smallest in Mongoloids...The colder environments of Europe and Northeast Asia selected for larger brains, greater intelligence, a reduction of inter-male aggression, and a reduction of testosterone levels and penis length...An elaboration of Rushton's r-K theory is that race differences in penis length may have evolved as an adaptation to population differences in the propensity for infidelity among human females."

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The evolution of fairness: Explaining variation in bargaining behavior

Shakti Lamba & Ruth Mace
Proceedings of the Royal Society: Biological Sciences, 7 January 2013

Abstract:
Conceptions of fairness vary across the world. Identifying the drivers of this variation is key to understanding the selection pressures and mechanisms that lead to the evolution of fairness in humans. Individuals' varying fairness preferences are widely assumed to represent cultural norms. However, this assumption has not previously been tested. Fairness norms are defined as culturally transmitted equilibria at which bargainers have coordinated expectations from each other. Hence, if fairness norms exist at the level of the ethno-linguistic group, we should observe two patterns. First, cultural conformism should maintain behavioural homogeneity within an ethno-linguistic group. Second, bargainers' expectations should be coordinated such that proposals and responses to proposals should covary. Here we show that neither of these patterns is observed across 21 populations of the same ethno-linguistic group, the Pahari Korwa of central India. Our findings suggest that what constitutes a fair division of resources can vary on smaller scales than that of the ethno-linguistic group. Individuals' local environments may play a central role in determining conceptions of fairness.

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The Biological Origin of Linguistic Diversity

Andrea Baronchelli et al.
PLoS ONE, October 2012

Abstract:
In contrast with animal communication systems, diversity is characteristic of almost every aspect of human language. Languages variously employ tones, clicks, or manual signs to signal differences in meaning; some languages lack the noun-verb distinction (e.g., Straits Salish), whereas others have a proliferation of fine-grained syntactic categories (e.g., Tzeltal); and some languages do without morphology (e.g., Mandarin), while others pack a whole sentence into a single word (e.g., Cayuga). A challenge for evolutionary biology is to reconcile the diversity of languages with the high degree of biological uniformity of their speakers. Here, we model processes of language change and geographical dispersion and find a consistent pressure for flexible learning, irrespective of the language being spoken. This pressure arises because flexible learners can best cope with the observed high rates of linguistic change associated with divergent cultural evolution following human migration. Thus, rather than genetic adaptations for specific aspects of language, such as recursion, the coevolution of genes and fast-changing linguistic structure provides the biological basis for linguistic diversity. Only biological adaptations for flexible learning combined with cultural evolution can explain how each child has the potential to learn any human language.

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Individual differences in the behavioral immune system and the emergence of cultural systems

Russ Clay, John Terrizzi & Natalie Shook
Social Psychology, Fall 2012, Pages 174-184

Abstract:
Cultural variation may be evoked through the interaction between domain-specific psychological mechanisms and environmental conditions (Gangestad, Haselton, & Buss, 2006). One such constellation of mechanisms is the behavioral immune system, a cluster of psychological processes evolved to promote disease-avoidance (Schaller, 2006). Previous research demonstrated that higher levels of both historic and contemporary pathogen prevalence are predictive of collectivism across geopolitical regions (Fincher, Thornhill, Murray, & Schaller, 2008). Across two studies, we demonstrate that individual differences in behavioral immune system reactivity (e.g., disgust sensitivity, germ aversion) are associated with variable endorsement of a vertical collectivist cultural orientation and differential value priorities, which are indicative of cultural differences. These findings provide support at an individual level for the proposition of evoked culture.

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The Emergence and Representation of Knowledge about Social and Nonsocial Hierarchies

Dharshan Kumaran, Hans Ludwig Melo & Emrah Duzel
Neuron, 8 November 2012, Pages 653-666

Abstract:
Primates are remarkably adept at ranking each other within social hierarchies, a capacity that is critical to successful group living. Surprisingly little, however, is understood about the neurobiology underlying this quintessential aspect of primate cognition. In our experiment, participants first acquired knowledge about a social and a nonsocial hierarchy and then used this information to guide investment decisions. We found that neural activity in the amygdala tracked the development of knowledge about a social, but not a nonsocial, hierarchy. Further, structural variations in amygdala gray matter volume accounted for interindividual differences in social transitivity performance. Finally, the amygdala expressed a neural signal selectively coding for social rank, whose robustness predicted the influence of rank on participants' investment decisions. In contrast, we observed that the linear structure of both social and nonsocial hierarchies was represented at a neural level in the hippocampus. Our study implicates the amygdala in the emergence and representation of knowledge about social hierarchies and distinguishes the domain-general contribution of the hippocampus.

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North African Populations Carry the Signature of Admixture with Neandertals

Federico Sánchez-Quinto et al.
PLoS ONE, October 2012

Abstract:
One of the main findings derived from the analysis of the Neandertal genome was the evidence for admixture between Neandertals and non-African modern humans. An alternative scenario is that the ancestral population of non-Africans was closer to Neandertals than to Africans because of ancient population substructure. Thus, the study of North African populations is crucial for testing both hypotheses. We analyzed a total of 780,000 SNPs in 125 individuals representing seven different North African locations and searched for their ancestral/derived state in comparison to different human populations and Neandertals. We found that North African populations have a significant excess of derived alleles shared with Neandertals, when compared to sub-Saharan Africans. This excess is similar to that found in non-African humans, a fact that can be interpreted as a sign of Neandertal admixture. Furthermore, the Neandertal's genetic signal is higher in populations with a local, pre-Neolithic North African ancestry. Therefore, the detected ancient admixture is not due to recent Near Eastern or European migrations. Sub-Saharan populations are the only ones not affected by the admixture event with Neandertals.

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Genomic Variation in Seven Khoe-San Groups Reveals Adaptation and Complex African History

Carina Schlebusch et al.
Science, 19 October 2012, Pages 374-379

Abstract:
The history of click-speaking Khoe-San, and African populations in general, remains poorly understood. We genotyped ∼2.3 million SNPs in 220 southern Africans and found that the Khoe-San diverged from other populations ≥100,000 years ago, but structure within the Khoe-San dated back to about 35,000 years ago. Genetic variation in various sub-Saharan populations did not localize the origin of modern humans to a single geographic region within Africa; instead, it indicated a history of admixture and stratification. We found evidence of adaptation targeting muscle function and immune response, potential adaptive introgression of UV-light protection, and selection predating modern human diversification involving skeletal and neurological development. These new findings illustrate the importance of African genomic diversity in understanding human evolutionary history.

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Ancient Admixture in Human History

Nick Patterson et al.
Genetics, 1 November 2012, Pages 1065-1093

Abstract:
Population mixture is an important process in biology. We present a suite of methods for learning about population mixtures, implemented in a software package called ADMIXTOOLS, that support formal tests for whether mixture occurred and make it possible to infer proportions and dates of mixture. We also describe the development of a new single nucleotide polymorphism (SNP) array consisting of 629,433 sites with clearly documented ascertainment that was specifically designed for population genetic analyses and that we genotyped in 934 individuals from 53 diverse populations. To illustrate the methods, we give a number of examples that provide new insights about the history of human admixture. The most striking finding is a clear signal of admixture into northern Europe, with one ancestral population related to present-day Basques and Sardinians and the other related to present-day populations of northeast Asia and the Americas. This likely reflects a history of admixture between Neolithic migrants and the indigenous Mesolithic population of Europe, consistent with recent analyses of ancient bones from Sweden and the sequencing of the genome of the Tyrolean "Iceman."

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Extremely Rare Interbreeding Events Can Explain Neanderthal DNA in Living Humans

Armando Neves & Maurizio Serva
PLoS ONE, October 2012

Abstract:
Considering the recent experimental discovery of Green et al that present-day non-Africans have 1 to 4% of their nuclear DNA of Neanderthal origin, we propose here a model which is able to quantify the genetic interbreeding between two subpopulations with equal fitness, living in the same geographic region. The model consists of a solvable system of deterministic ordinary differential equations containing as a stochastic ingredient a realization of the neutral Wright-Fisher process. By simulating the stochastic part of the model we are able to apply it to the interbreeding of the African ancestors of Eurasians and Middle Eastern Neanderthal subpopulations and estimate the only parameter of the model, which is the number of individuals per generation exchanged between subpopulations. Our results indicate that the amount of Neanderthal DNA in living non-Africans can be explained with maximum probability by the exchange of a single pair of individuals between the subpopulations at each 77 generations, but larger exchange frequencies are also allowed with sizeable probability. The results are compatible with a long coexistence time of 130,000 years, a total interbreeding population of 10^4 order individuals, and with all living humans being descendants of Africans both for mitochondrial DNA and Y chromosome.

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Synthesis between demic and cultural diffusion in the Neolithic transition in Europe

Joaquim Fort
Proceedings of the National Academy of Sciences, 13 November 2012, Pages 18669-18673

Abstract:
There is a long-standing controversy between two models of the Neolithic transition. The demic model assumes that the Neolithic range expansion was mainly due to the spread of populations, and the cultural model considers that it was essentially due to the spread of ideas. Here we integrate the demic and cultural models in a unified framework. We show that cultural diffusion explains ∼40% of the spread rate of the Neolithic transition in Europe, as implied by archaeological data. Thus, cultural diffusion cannot be neglected, but demic diffusion was the most important mechanism in this major historical process at the continental scale. This quantitative approach can be useful also in regional analysis, the description of Neolithic transitions in other continents, and models of many human spread phenomena.

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Grooming and group cohesion in primates: Implications for the evolution of language

Cyril Grueter et al.
Evolution and Human Behavior, forthcoming

Abstract:
It is well established that allogrooming, which evolved for a hygienic function, has acquired an important derived social function in many primates. In particular, it has been postulated that grooming may play an essential role in group cohesion and that human language, as verbal grooming or gossip, evolved to maintain group cohesion in the hominin lineage with its unusually large group sizes. Here, we examine this group cohesion hypothesis and test it against the alternative grooming-need hypothesis which posits that rates of grooming are higher in species where grooming need (i.e. the motivation to groom for hygiene and its associated psychological reward) is more pronounced. This alternative predicts that the derived social function of grooming evolved mostly in those lineages that had the highest exposure to ectoparasites and dirt, i.e. terrestrial species. A detailed comparative analysis of 74 species of wild primates, controlling for phylogenetic non-independence, showed that terrestriality was a highly significant predictor of allogrooming time, consistent with the prediction. The predictions of the group cohesion hypothesis were not supported, however. Group size did not predict grooming time across primates, nor did it do so in separate intra-population analyses in 17 species. Thus, there is no comparative support for the group-cohesion function of allogrooming, which questions the role of grooming in the evolution of human language.

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Genome-Wide Association Studies of Quantitatively Measured Skin, Hair, and Eye Pigmentation in Four European Populations

Sophie Candille et al.
PLoS ONE, October 2012

Abstract:
Pigmentation of the skin, hair, and eyes varies both within and between human populations. Identifying the genes and alleles underlying this variation has been the goal of many candidate gene and several genome-wide association studies (GWAS). Most GWAS for pigmentary traits to date have been based on subjective phenotypes using categorical scales. But skin, hair, and eye pigmentation vary continuously. Here, we seek to characterize quantitative variation in these traits objectively and accurately and to determine their genetic basis. Objective and quantitative measures of skin, hair, and eye color were made using reflectance or digital spectroscopy in Europeans from Ireland, Poland, Italy, and Portugal. A GWAS was conducted for the three quantitative pigmentation phenotypes in 176 women across 313,763 SNP loci, and replication of the most significant associations was attempted in a sample of 294 European men and women from the same countries. We find that the pigmentation phenotypes are highly stratified along axes of European genetic differentiation. The country of sampling explains approximately 35% of the variation in skin pigmentation, 31% of the variation in hair pigmentation, and 40% of the variation in eye pigmentation. All three quantitative phenotypes are correlated with each other. In our two-stage association study, we reproduce the association of rs1667394 at the OCA2/HERC2 locus with eye color but we do not identify new genetic determinants of skin and hair pigmentation supporting the lack of major genes affecting skin and hair color variation within Europe and suggesting that not only careful phenotyping but also larger cohorts are required to understand the genetic architecture of these complex quantitative traits. Interestingly, we also see that in each of these four populations, men are more lightly pigmented in the unexposed skin of the inner arm than women, a fact that is underappreciated and may vary across the world.

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Climate impacts on human settlement and agricultural activities in northern Norway revealed through sediment biogeochemistry

Robert D'Anjou et al.
Proceedings of the National Academy of Sciences, 11 December 2012, Pages 20332-20337

Abstract:
Disentangling the effects of climate change and anthropogenic activities on the environment is a major challenge in paleoenvironmental research. Here, we used fecal sterols and other biogeochemical compounds in lake sediments from northern Norway to identify both natural and anthropogenic signals of environmental change during the late Holocene. The area was first occupied by humans and their grazing animals at ∼2,250 ± 75 calendar years before 1950 AD (calendar years before present). The arrival of humans is indicated by an abrupt increase in coprostanol (and its epimer epicoprostanol) in the sediments and an associated increase in 5β-stigmastanol (and 5β-epistigmastanol), which resulted from human and animal feces washing into the lake. Human settlement was accompanied by an abrupt increase in landscape fires (indicated by the rise in pyrolytic polycyclic aromatic hydrocarbons) and a decline in woodland (registered by a change in n-alkane chain lengths from leaf waxes), accelerating a process that began earlier in the Holocene. Human activity and associated landscape changes in the region over the last two millennia were mainly driven by summer temperatures, as indicated by independent tree-ring reconstructions, although there were periods when socioeconomic factors played an equally important role. In this study, fecal sterols in lake sediments have been used to provide a record of human occupancy through time. This approach may be useful in many archeological studies, both to confirm the presence of humans and grazing animals, and to distinguish between anthropogenic and natural factors that have influenced the environment in the past.

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Adaptive Evolution of the FADS Gene Cluster within Africa

Rasika Mathias et al.
PLoS ONE, September 2012

Abstract:
Long chain polyunsaturated fatty acids (LC-PUFAs) are essential for brain structure, development, and function, and adequate dietary quantities of LC-PUFAs are thought to have been necessary for both brain expansion and the increase in brain complexity observed during modern human evolution. Previous studies conducted in largely European populations suggest that humans have limited capacity to synthesize brain LC-PUFAs such as docosahexaenoic acid (DHA) from plant-based medium chain (MC) PUFAs due to limited desaturase activity. Population-based differences in LC-PUFA levels and their product-to-substrate ratios can, in part, be explained by polymorphisms in the fatty acid desaturase (FADS) gene cluster, which have been associated with increased conversion of MC-PUFAs to LC-PUFAs. Here, we show evidence that these high efficiency converter alleles in the FADS gene cluster were likely driven to near fixation in African populations by positive selection ~85 kya. We hypothesize that selection at FADS variants, which increase LC-PUFA synthesis from plant-based MC-PUFAs, played an important role in allowing African populations obligatorily tethered to marine sources for LC-PUFAs in isolated geographic regions, to rapidly expand throughout the African continent 60-80 kya.

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Mice, scats and burials: Unusual concentrations of microfauna found in human burials at the Neolithic site of Çatalhöyük, Central Anatolia

Emma Jenkins
Journal of Social Archaeology, October 2012, Pages 380-403

Abstract:
Three human burials were found at Çatalhöyük that contained large microfaunal assemblages. Taphonomic analysis demonstrated that many of these elements had passed through the digestive tract of a small carnivore, indicating that the microfauna entered the burials in carnivore scats rather than as carcasses. One of the burials in particular (F. 513) contained an enormous quantity of microfauna which was concentrated over the torso of the body. It is concluded that the scats were deliberately placed in the burials by the human inhabitants of the site as part of ritualistic practice. Furthermore, it is suggested that small carnivores were encouraged to enter Çatalhöyük in order to control house mice, and other small mammal, numbers.

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The Pace of Cultural Evolution

Charles Perreault
PLoS ONE, September 2012

Abstract:
Today, humans inhabit most of the world's terrestrial habitats. This observation has been explained by the fact that we possess a secondary inheritance mechanism, culture, in addition to a genetic system. Because it is assumed that cultural evolution occurs faster than biological evolution, humans can adapt to new ecosystems more rapidly than other animals. This assumption, however, has never been tested empirically. Here, I compare rates of change in human technologies to rates of change in animal morphologies. I find that rates of cultural evolution are inversely correlated with the time interval over which they are measured, which is similar to what is known for biological rates. This correlation explains why the pace of cultural evolution appears faster when measured over recent time periods, where time intervals are often shorter. Controlling for the correlation between rates and time intervals, I show that (1) cultural evolution is faster than biological evolution; (2) this effect holds true even when the generation time of species is controlled for; and (3) culture allows us to evolve over short time scales, which are normally accessible only to short-lived species, while at the same time allowing for us to enjoy the benefits of having a long life history.

By KEVIN LEWIS | 09:00:00 AM