Prehistoric
A Revised Timescale for Human Evolution Based on Ancient Mitochondrial Genomes
Qiaomei Fu et al.
Current Biology, forthcoming
Background: Recent analyses of de novo DNA mutations in modern humans have suggested a nuclear substitution rate that is approximately half that of previous estimates based on fossil calibration. This result has led to suggestions that major events in human evolution occurred far earlier than previously thought.
Results: Here, we use mitochondrial genome sequences from ten securely dated ancient modern humans spanning 40,000 years as calibration points for the mitochondrial clock, thus yielding a direct estimate of the mitochondrial substitution rate. Our clock yields mitochondrial divergence times that are in agreement with earlier estimates based on calibration points derived from either fossils or archaeological material. In particular, our results imply a separation of non-Africans from the most closely related sub-Saharan African mitochondrial DNAs (haplogroup L3) that occurred less than 62-95 kya.
Conclusions: Though single loci like mitochondrial DNA (mtDNA) can only provide biased estimates of population divergence times, they can provide valid upper bounds. Our results exclude most of the older dates for African and non-African population divergences recently suggested by de novo mutation rate estimates in the nuclear genome.
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Anthony Ortmann & Tristram Kidder
Geoarchaeology, January/February 2013, Pages 66-86
Abstract:
Hunter-gatherer societies are often characterized by limited complexity and social equality. Therefore, the construction of monumental architecture by hunter-gatherers is seen as the manifestation of social and political inequality. The massive size and rapid construction of Mound A at Poverty Point (ca. 3261 cal. yr B.P.) in northeast Louisiana challenges these notions. Geoarchaeological investigations of stratigraphy at the macro- and micro-levels shows there are no erosion events, natural episodes of soil formation, or cultural stages. We infer from these results that Mound A was constructed by a large labor force over a short period of time. There is no evidence, however, that the mound was constructed under the aegis of a ranked socio-political system. We argue instead that the mound was constructed as a ritual feature and that leadership required to mobilize labor and resources was situational and emerged through ritual practice that developed because of the need to integrate a large population.
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Fernando Mendez et al.
American Journal of Human Genetics, March 2013, Pages 454-459
Abstract:
We report the discovery of an African American Y chromosome that carries the ancestral state of all SNPs that defined the basal portion of the Y chromosome phylogenetic tree. We sequenced ∼240 kb of this chromosome to identify private, derived mutations on this lineage, which we named A00. We then estimated the time to the most recent common ancestor (TMRCA) for the Y tree as 338 thousand years ago (kya) (95% confidence interval = 237-581 kya). Remarkably, this exceeds current estimates of the mtDNA TMRCA, as well as those of the age of the oldest anatomically modern human fossils. The extremely ancient age combined with the rarity of the A00 lineage, which we also find at very low frequency in central Africa, point to the importance of considering more complex models for the origin of Y chromosome diversity. These models include ancient population structure and the possibility of archaic introgression of Y chromosomes into anatomically modern humans. The A00 lineage was discovered in a large database of consumer samples of African Americans and has not been identified in traditional hunter-gatherer populations from sub-Saharan Africa. This underscores how the stochastic nature of the genealogical process can affect inference from a single locus and warrants caution during the interpretation of the geographic location of divergent branches of the Y chromosome phylogenetic tree for the elucidation of human origins.
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Universal distribution of component frequencies in biological and technological systems
Tin Yau Pang & Sergei Maslov
Proceedings of the National Academy of Sciences, forthcoming
Abstract:
Bacterial genomes and large-scale computer software projects both consist of a large number of components (genes or software packages) connected via a network of mutual dependencies. Components can be easily added or removed from individual systems, and their use frequencies vary over many orders of magnitude. We study this frequency distribution in genomes of ∼500 bacterial species and in over 2 million Linux computers and find that in both cases it is described by the same scale-free power-law distribution with an additional peak near the tail of the distribution corresponding to nearly universal components. We argue that the existence of a power law distribution of frequencies of components is a general property of any modular system with a multilayered dependency network. We demonstrate that the frequency of a component is positively correlated with its dependency degree given by the total number of upstream components whose operation directly or indirectly depends on the selected component. The observed frequency/dependency degree distributions are reproduced in a simple mathematically tractable model introduced and analyzed in this study.
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Karin Isler & Carel van Schaik
Current Anthropology, December 2012, Pages S453-S465
Abstract:
The "expensive brain" framework proposes that the costs of an increase in brain size can be met by any combination of increasing the total energy turnover or reducing energy allocation to other expensive functions, such as maintenance (digestion), locomotion, or production (growth and reproduction). Here, we explore its implications for human evolution. Using both comparative data on extant mammals and life-table simulations from wild extant apes, we show that primates with a hominoid lifestyle face a gray ceiling that limits their brain size, with larger values leading to demographic nonviability. We argue that cooperative care provides the most plausible exaptation for the increase in brain size in the Homo lineage.
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Eiluned Pearce, Chris Stringer & R.I.M. Dunbar
Proceedings of the Royal Society: Biological Sciences, 7 May 2013
Abstract:
Previous research has identified morphological differences between the brains of Neanderthals and anatomically modern humans (AMHs). However, studies using endocasts or the cranium itself are limited to investigating external surface features and the overall size and shape of the brain. A complementary approach uses comparative primate data to estimate the size of internal brain areas. Previous attempts to do this have generally assumed that identical total brain volumes imply identical internal organization. Here, we argue that, in the case of Neanderthals and AMHs, differences in the size of the body and visual system imply differences in organization between the same-sized brains of these two taxa. We show that Neanderthals had significantly larger visual systems than contemporary AMHs (indexed by orbital volume) and that when this, along with their greater body mass, is taken into account, Neanderthals have significantly smaller adjusted endocranial capacities than contemporary AMHs. We discuss possible implications of differing brain organization in terms of social cognition, and consider these in the context of differing abilities to cope with fluctuating resources and cultural maintenance.
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Stature, Body Mass, and Brain Size: A Two-Million-Year Odyssey
Andrew Gallagher
Economics & Human Biology, forthcoming
Abstract:
Physical size has been critical in the evolutionary success of the genus Homo over the past 2.4 million-years. An acceleration in the expansion of savannah grasslands in Africa from 1.6 Ma - 1.2 Ma witnessed concomitant increases in physical stature (150 cm-170 cm), weight (50 kg-70 kg), and brain size (750 cc's-900 cc's). With the onset of 100,000 year Middle Pleistocene glacial cycles ("ice ages") some 780,000 years ago, large-bodied Homo groups had reached modern size and had successfully dispersed from equatorial Africa, Central, and Southeast Asia to high-latitude localities in Atlantic Europe and North East Asia. While there is support for incursions of multiple Homo lineages to West Asia and Continental Europe at this time, data does not favour a persistence of Homo erectus beyond ∼ 400,000 years ago in Africa, west and Central Asia, and Europe. Novel Middle Pleistocene Homo forms (780,000-400,000 years) may not have been substantially taller (150-170 cm) than earlier Homo (1.6 Ma-800,000 years), yet brain size exceeded 1000 cc's and body mass approached 80 kg in some males. Later Pleistocene Homo (400,000-138,000 years) were ‘massive' in their height (160-190 cm) and mass (70-90 kg) and consistently exceed recent humans. Relative brain size exceeds earlier Homo, yet is substantially lower than in final glacial H. sapiens and H. neanderthalensis. A final leap in absolute and relative brain size in Homo (300,000-138,000 years) occurred independent of any observed increase in body mass and implies a different selective mediator to that operating on brain size increases observed in earlier Homo.
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Tree climbing and human evolution
Vivek Venkataraman, Thomas Kraft & Nathaniel Dominy
Proceedings of the National Academy of Sciences, 22 January 2013, Pages 1237-1242
Abstract:
Paleoanthropologists have long argued - often contentiously - about the climbing abilities of early hominins and whether a foot adapted to terrestrial bipedalism constrained regular access to trees. However, some modern humans climb tall trees routinely in pursuit of honey, fruit, and game, often without the aid of tools or support systems. Mortality and morbidity associated with facultative arboreality is expected to favor behaviors and anatomies that facilitate safe and efficient climbing. Here we show that Twa hunter-gatherers use extraordinary ankle dorsiflexion (>45°) during climbing, similar to the degree observed in wild chimpanzees. Although we did not detect a skeletal signature of dorsiflexion in museum specimens of climbing hunter-gatherers from the Ituri forest, we did find that climbing by the Twa is associated with longer fibers in the gastrocnemius muscle relative to those of neighboring, nonclimbing agriculturalists. This result suggests that a more excursive calf muscle facilitates climbing with a bipedally adapted ankle and foot by positioning the climber closer to the tree, and it might be among the mechanisms that allow hunter-gatherers to access the canopy safely. Given that we did not find a skeletal correlate for this observed behavior, our results imply that derived aspects of the hominin ankle associated with bipedalism remain compatible with vertical climbing and arboreal resource acquisition. Our findings challenge the persistent arboreal-terrestrial dichotomy that has informed behavioral reconstructions of fossil hominins and highlight the value of using modern humans as models for inferring the limits of hominin arboreality.
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Richard Bribiescas, Peter Ellison & Peter Gray
Current Anthropology, December 2012, Pages S424-S435
Abstract:
The evolution of male life history traits was central to the emergence of the genus Homo. Compared with earlier hominins, changes in the behavioral and physiological mechanics of growth, survivorship, reproductive effort, and senescence all likely contributed to shifts in how males contributed to the evolution of our genus. For example, the range of paternal investment in modern Homo sapiens is unusual compared with most mammals and primates, all but certainly contributing to the evolution of the suite of life history traits that define Homo, including high fertility, large bodies, altricial offspring, large brains, and long lives. Moreover, the extensive range of phenotypic and behavioral variation in somatic and behavioral reflections of male reproductive effort across modern H. sapiens is especially noteworthy. We propose that selection for a broad range of variation in traits reflective of male reproductive effort was important to the evolution of Homo. We examine factors that contribute to this variation, proposing that selection for paternal and somatic investment plasticity across the entire male life span was important for the evolution of Homo. Potential research strategies and directions for new research for exploring these issues in the fossil record are also discussed.
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Genome-Wide Diversity in the Levant Reveals Recent Structuring by Culture
Marc Haber et al.
PLoS Genetics, February 2013
Abstract:
The Levant is a region in the Near East with an impressive record of continuous human existence and major cultural developments since the Paleolithic period. Genetic and archeological studies present solid evidence placing the Middle East and the Arabian Peninsula as the first stepping-stone outside Africa. There is, however, little understanding of demographic changes in the Middle East, particularly the Levant, after the first Out-of-Africa expansion and how the Levantine peoples relate genetically to each other and to their neighbors. In this study we analyze more than 500,000 genome-wide SNPs in 1,341 new samples from the Levant and compare them to samples from 48 populations worldwide. Our results show recent genetic stratifications in the Levant are driven by the religious affiliations of the populations within the region. Cultural changes within the last two millennia appear to have facilitated/maintained admixture between culturally similar populations from the Levant, Arabian Peninsula, and Africa. The same cultural changes seem to have resulted in genetic isolation of other groups by limiting admixture with culturally different neighboring populations. Consequently, Levant populations today fall into two main groups: one sharing more genetic characteristics with modern-day Europeans and Central Asians, and the other with closer genetic affinities to other Middle Easterners and Africans. Finally, we identify a putative Levantine ancestral component that diverged from other Middle Easterners ~23,700-15,500 years ago during the last glacial period, and diverged from Europeans ~15,900-9,100 years ago between the last glacial warming and the start of the Neolithic.
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Climatic Fluctuations and the Diffusion of Agriculture
Quamrul Ashraf & Stelios Michalopoulos
NBER Working Paper, February 2013
Abstract:
This research examines variations in the diffusion of agriculture across countries and archaeological sites. The theory suggests that a society's history of climatic shocks shaped the timing of its adoption of farming. Specifically, as long as climatic disturbances did not lead to a collapse of the underlying resource base, the rate at which foragers were climatically propelled to experiment with their habitats determined the accumulation of tacit knowledge complementary to farming. Thus, differences in climatic volatility across hunter-gatherer societies gave rise to the observed spatial variation in the timing of the adoption of agriculture. Consistent with the proposed hypothesis, the empirical investigation demonstrates that, conditional on biogeographic endowments, climatic volatility has a non-monotonic effect on the timing of the adoption of agriculture. Farming diffused earlier across regions characterized by intermediate levels of climatic fluctuations, with those subjected to either too high or too low intertemporal variability transiting later.
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A continuous climatic impact on Holocene human population in the Rocky Mountains
Robert Kelly et al.
Proceedings of the National Academy of Sciences, 8 January 2013, Pages 443-447
Abstract:
Ancient cultural changes have often been linked to abrupt climatic events, but the potential that climate can exert a persistent influence on human populations has been debated. Here, independent population, temperature, and moisture history reconstructions from the Bighorn Basin in Wyoming (United States) show a clear quantitative relationship spanning 13 ka, which explains five major periods of population growth/decline and ∼45% of the population variance. A persistent ∼300-y lag in the human demographic response conforms with either slow (∼0.3%) intrinsic annual population growth rates or a lag in the environmental carrying capacity, but in either case, the population continuously adjusted to changing environmental conditions.
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Andrea Bamberg Migliano & Myrtille Guillon
Current Anthropology, December 2012, Pages S359-S368
Abstract:
The increase in body size observed with the appearance and evolution of Homo is most often attributed to thermoregulatory and locomotor adaptations to environment; increased reliance on animal protein and fat; or increased behavioral flexibility, provisioning, and cooperation leading to decreased mortality rates and slow life histories. It is not easy to test these hypotheses in the fossil record. Therefore, understanding selective pressures shaping height variability in living humans might help to construct models for the interpretation of body size variation in the hominins. Among human populations, average male height varies extensively (145 cm-183 cm); a similar range of variation is found in Homo erectus (including African and Georgian samples). Previous research shows that height in human populations covaries with life history traits and variations in mortality rates and that different environments affect adult height through adaptations related to thermoregulation and nutrition. We investigate the interactions between life history traits, mortality rates, environmental setting, and subsistence for 89 small-scale societies. We show that mortality rates are the primary factor shaping adult height variation and that people in savanna are consistently taller than people in forests. We focus on relevant results for interpreting the evolution of Homo body size variability.
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Reconstructing Roma History from Genome-Wide Data
Priya Moorjani et al.
PLoS ONE, March 2013
Abstract:
The Roma people, living throughout Europe and West Asia, are a diverse population linked by the Romani language and culture. Previous linguistic and genetic studies have suggested that the Roma migrated into Europe from South Asia about 1,000-1,500 years ago. Genetic inferences about Roma history have mostly focused on the Y chromosome and mitochondrial DNA. To explore what additional information can be learned from genome-wide data, we analyzed data from six Roma groups that we genotyped at hundreds of thousands of single nucleotide polymorphisms (SNPs). We estimate that the Roma harbor about 80% West Eurasian ancestry-derived from a combination of European and South Asian sources-and that the date of admixture of South Asian and European ancestry was about 850 years before present. We provide evidence for Eastern Europe being a major source of European ancestry, and North-west India being a major source of the South Asian ancestry in the Roma. By computing allele sharing as a measure of linkage disequilibrium, we estimate that the migration of Roma out of the Indian subcontinent was accompanied by a severe founder event, which appears to have been followed by a major demographic expansion after the arrival in Europe.
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Communal breeding promotes a matrilineal social system where husband and wife live apart
Jia-Jia Wu et al.
Proceedings of the Royal Society: Biological Sciences, 7 May 2013
Abstract:
The matrilineal Mosuo of southwest China live in large communal houses where brothers and sisters of three generations live together, and adult males walk to visit their wives only at night; hence males do not reside with their own offspring. This duolocal residence with ‘walking' or ‘visiting' marriage is described in only a handful of matrilineal peasant societies. Benefits to women of living with matrilineal kin, who cooperate with child-care, are clear. But why any kinship system can evolve where males invest more in their sister's offspring than their own is a puzzle for evolutionary anthropologists. Here, we present a new hypothesis for a matrilineal bias in male investment. We argue that, when household resources are communal, relatedness to the whole household matters more than relatedness to individual offspring. We use an inclusive fitness model to show that the more sisters (and other closely related females) co-reside, the more effort males should spend working on their sister's farm and less on their wife's farm. The model shows that paternity uncertainty may be a cause of lower overall work rates in males, but it is not likely to be the cause of a matrilineal bias. The bias in work effort towards working on their natal farm, and thus the duolocal residence and ‘visiting marriage' system, can be understood as maximizing inclusive fitness in circumstances where female kin breed communally.
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Genome-wide data substantiate Holocene gene flow from India to Australia
Irina Pugach et al.
Proceedings of the National Academy of Sciences, 29 January 2013, Pages 1803-1808
Abstract:
The Australian continent holds some of the earliest archaeological evidence for the expansion of modern humans out of Africa, with initial occupation at least 40,000 y ago. It is commonly assumed that Australia remained largely isolated following initial colonization, but the genetic history of Australians has not been explored in detail to address this issue. Here, we analyze large-scale genotyping data from aboriginal Australians, New Guineans, island Southeast Asians and Indians. We find an ancient association between Australia, New Guinea, and the Mamanwa (a Negrito group from the Philippines), with divergence times for these groups estimated at 36,000 y ago, and supporting the view that these populations represent the descendants of an early "southern route" migration out of Africa, whereas other populations in the region arrived later by a separate dispersal. We also detect a signal indicative of substantial gene flow between the Indian populations and Australia well before European contact, contrary to the prevailing view that there was no contact between Australia and the rest of the world. We estimate this gene flow to have occurred during the Holocene, 4,230 y ago. This is also approximately when changes in tool technology, food processing, and the dingo appear in the Australian archaeological record, suggesting that these may be related to the migration from India.
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The emergence of hierarchical structure in human language
Shigeru Miyagawa, Robert Berwick & Kazuo Okanoya
Frontiers in Psychology, February 2013
Abstract:
We propose a novel account for the emergence of human language syntax. Like many evolutionary innovations, language arose from the adventitious combination of two pre-existing, simpler systems that had been evolved for other functional tasks. The first system, Type E(xpression), is found in birdsong, where the same song marks territory, mating availability, and similar "expressive" functions. The second system, Type L(exical), has been suggestively found in non-human primate calls and in honeybee waggle dances, where it demarcates predicates with one or more "arguments," such as combinations of calls in monkeys or compass headings set to sun position in honeybees. We show that human language syntax is composed of two layers that parallel these two independently evolved systems: an "E" layer resembling the Type E system of birdsong and an "L" layer providing words. The existence of the "E" and "L" layers can be confirmed using standard linguistic methodology. Each layer, E and L, when considered separately, is characterizable as a finite state system, as observed in several non-human species. When the two systems are put together they interact, yielding the unbounded, non-finite state, hierarchical structure that serves as the hallmark of full-fledged human language syntax. In this way, we account for the appearance of a novel function, language, within a conventional Darwinian framework, along with its apparently unique emergence in a single species.
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Transformation of social networks in the late pre-Hispanic US Southwest
Barbara Mills et al.
Proceedings of the National Academy of Sciences, forthcoming
Abstract:
The late pre-Hispanic period in the US Southwest (A.D. 1200-1450) was characterized by large-scale demographic changes, including long-distance migration and population aggregation. To reconstruct how these processes reshaped social networks, we compiled a comprehensive artifact database from major sites dating to this interval in the western Southwest. We combine social network analysis with geographic information systems approaches to reconstruct network dynamics over 250 y. We show how social networks were transformed across the region at previously undocumented spatial, temporal, and social scales. Using well-dated decorated ceramics, we track changes in network topology at 50-y intervals to show a dramatic shift in network density and settlement centrality from the northern to the southern Southwest after A.D. 1300. Both obsidian sourcing and ceramic data demonstrate that long-distance network relationships also shifted from north to south after migration. Surprisingly, social distance does not always correlate with spatial distance because of the presence of network relationships spanning long geographic distances. Our research shows how a large network in the southern Southwest grew and then collapsed, whereas networks became more fragmented in the northern Southwest but persisted. The study also illustrates how formal social network analysis may be applied to large-scale databases of material culture to illustrate multigenerational changes in network structure.
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Ecological constraints on the first prehistoric farmers in Europe
William Banks et al.
Journal of Archaeological Science, June 2013, Pages 2746-2753
Abstract:
The Neolithic Revolution, which witnessed the transformation of hunter-gatherer groups into farming communities, is traditionally viewed as the event that allowed human groups to create systems of production that, in the long run, led to present-day societies. Despite the large corpus of research focused on the mechanisms and outcomes of the Neolithic transition, relatively little effort has been devoted to evaluating whether particular production-oriented adaptations could be integrated into a broad range of ecological conditions, and if specific cultural traditions differed ecologically. In order to investigate whether the differences between the adaptations and geographic distributions of three major Early Neolithic archaeological cultures are related to the exploitation of different suites of environmental conditions, we apply genetic algorithm and maximum entropy ecological niche modeling techniques to reconstruct and compare the ecological niches within which three principal Neolithic cultures (Impressed Ware, Cardial Ware, and Linearbandkeramik) spread across Europe between ca. 8000-7000 cal yr BP. Results show that these cultures occupied mutually exclusive suites of environmental conditions and, thus, were adapted to distinct and essentially non-overlapping ecological niches. We argue that the historical processes behind the Neolithization of Europe were influenced by environmental factors predisposing occupation of regions most suited to specific cultural adaptations.
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Ecosystem variability and early human habitats in eastern Africa
Clayton Magill, Gail Ashley & Katherine Freeman
Proceedings of the National Academy of Sciences, 22 January 2013, Pages 1167-1174
Abstract:
The role of savannas during the course of early human evolution has been debated for nearly a century, in part because of difficulties in characterizing local ecosystems from fossil and sediment records. Here, we present high-resolution lipid biomarker and isotopic signatures for organic matter preserved in lake sediments at Olduvai Gorge during a key juncture in human evolution about 2.0 Ma-the emergence and dispersal of Homo erectus (sensu lato). Using published data for modern plants and soils, we construct a framework for ecological interpretations of stable carbon-isotope compositions (expressed as δ13C values) of lipid biomarkers from ancient plants. Within this framework, δ13C values for sedimentary leaf lipids and total organic carbon from Olduvai Gorge indicate recurrent ecosystem variations, where open C4 grasslands abruptly transitioned to closed C3 forests within several hundreds to thousands of years. Carbon-isotopic signatures correlate most strongly with Earth's orbital geometry (precession), and tropical sea-surface temperatures are significant secondary predictors in partial regression analyses. The scale and pace of repeated ecosystem variations at Olduvai Gorge contrast with long-held views of directional or stepwise aridification and grassland expansion in eastern Africa during the early Pleistocene and provide a local perspective on environmental hypotheses of human evolution.