Hunter–gatherers have less famine than agriculturalists

The idea that hunter–gatherer societies experience more frequent famine than societies with other modes of subsistence is pervasive in the literature on human evolution. This idea underpins, for example, the ‘thrifty genotype hypothesis’. This hypothesis proposes that our hunter–gatherer ancestors were adapted to frequent famines, and that these once adaptive ‘thrifty genotypes’ are now responsible for the current obesity epidemic. The suggestion that hunter–gatherers are more prone to famine also underlies the widespread assumption that these societies live in marginal habitats. Despite the ubiquity of references to ‘feast and famine’ in the literature describing our hunter–gatherer ancestors, it has rarely been tested whether hunter–gatherers suffer from more famine than other societies. Here, we analyse famine frequency and severity in a large cross-cultural database, in order to explore relationships between subsistence and famine risk. This is the first study to report that, if we control for habitat quality, hunter–gatherers actually had significantly less—not more—famine than other subsistence modes. This finding challenges some of the assumptions underlying for models of the evolution of the human diet, as well as our understanding of the recent epidemic of obesity and type 2 diabetes mellitus.     

Recent Origin and Cultural Reversion of a Hunter–Gatherer Group

Contemporary hunter–gatherer groups are often thought to serve as models of an ancient lifestyle that was typical of human populations prior to the development of agriculture. Patterns of genetic variation in hunter–gatherer groups such as the !Kung and African Pygmies are consistent with this view, as they exhibit low genetic diversity coupled with high frequencies of divergent mtDNA types not found in surrounding agricultural groups, suggesting long-term isolation and small population sizes. We report here genetic evidence concerning the origins of the Mlabri, an enigmatic hunter–gatherer group from northern Thailand. The Mlabri have no mtDNA diversity, and the genetic diversity at Y-chromosome and autosomal loci are also extraordinarily reduced in the Mlabri. Genetic, linguistic, and cultural data all suggest that the Mlabri were recently founded, 500–800 y ago, from a very small number of individuals. Moreover, the Mlabri appear to have originated from an agricultural group and then adopted a hunting–gathering subsistence mode. This example of cultural reversion from agriculture to a hunting–gathering lifestyle indicates that contemporary hunter–gatherer groups do not necessarily reflect a pre-agricultural lifestyle.     

Insights into the demographic history of African Pygmies from complete mitochondrial genomes

Pygmy populations are among the few hunter-gatherers currently living in sub-Saharan Africa and are mainly represented by two groups, Eastern and Western, according to their current geographical distribution. They are scattered across the Central African belt and surrounded by Bantu-speaking farmers, with whom they have complex social and economic interactions. To investigate the demographic history of Pygmy groups, a population approach was applied to the analysis of 205 complete mitochondrial DNA (mtDNA) sequences from ten central African populations. No sharing of maternal lineages was observed between the two Pygmy groups, with haplogroup L1c being characteristic of the Western group but most of Eastern Pygmy lineages falling into subclades of L0a, L2a, and L5. Demographic inferences based on Bayesian coalescent simulations point to an early split among the maternal ancestors of Pygmies and those of Bantu-speaking farmers (～ 70,000 years ago [ya]). Evidence for population growth in the ancestors of Bantu-speaking farmers has been observed, starting ～ 65,000 ya, well before the diffusion of Bantu languages. Subsequently, the effective population size of the ancestors of Pygmies remained constant over time and ～ 27,000 ya, coincident with the Last Glacial Maximum, Eastern and Western Pygmies diverged, with evidence of subsequent migration only among the Western group and the Bantu-speaking farmers. Western Pygmies show signs of a recent bottleneck 4,000-650 ya, coincident with the diffusion of Bantu languages, whereas Eastern Pygmies seem to have experienced a more ancient decrease in population size (20,000-4,000 ya). In conclusion, the results of this first attempt at analyzing complete mtDNA sequences at the population level in sub-Saharan Africa not only support previous findings but also offer new insights into the demographic history of Pygmy populations, shedding new light on the ancient peopling of the African continent.     

Limited dispersal in mobile hunter–gatherer Baka Pygmies

Hunter–gatherer Pygmies from Central Africa are described as being extremely mobile. Using neutral genetic markers and population genetics theory, we explored the dispersal behaviour of the Baka Pygmies from Cameroon, one of the largest Pygmy populations in Central Africa. We found a strong correlation between genetic and geographical distances: a pattern of isolation by distance arising from limited parent–offspring dispersal. Our study suggests that mobile hunter–gatherers do not necessarily disperse over wide geographical areas.     

Ancient mitochondrial DNA from the northern fringe of the Neolithic farming expansion in Europe sheds light on the dispersion process

The European Neolithization process started around 12 000 years ago in the Near East. The introduction of agriculture spread north and west throughout Europe and a key question has been if this was brought about by migrating individuals, by an exchange of ideas or a by a mixture of these. The earliest farming evidence in Scandinavia is found within the Funnel Beaker Culture complex (Trichterbecherkultur, TRB) which represents the northernmost extension of Neolithic farmers in Europe. The TRB coexisted for almost a millennium with hunter–gatherers of the Pitted Ware Cultural complex (PWC). If migration was a substantial part of the Neolithization, even the northerly TRB community would display a closer genetic affinity to other farmer populations than to hunter–gatherer populations. We deep-sequenced the mitochondrial hypervariable region 1 from seven farmers (six TRB and one Battle Axe complex, BAC) and 13 hunter–gatherers (PWC) and authenticated the sequences using postmortem DNA damage patterns. A comparison with 124 previously published sequences from prehistoric Europe shows that the TRB individuals share a close affinity to Central European farmer populations, and that they are distinct from hunter–gatherer groups, including the geographically close and partially contemporary PWC that show a close affinity to the European Mesolithic hunter–gatherers.     

Skull and limb morphology differentially track population history and environmental factors in the transition to agriculture in Europe

The Neolithic transition in Europe was a complex mosaic spatio-temporal process, involving both demic diffusion from the Near East and the cultural adoption of farming practices by indigenous hunter–gatherers. Previous analyses of Mesolithic hunter–gatherers and Early Neolithic farmers suggest that cranial shape variation preserves the population history signature of the Neolithic transition. However, the extent to which these same demographic processes are discernible in the postcranium is poorly understood. Here, for the first time, crania and postcranial elements from the same 11 prehistoric populations are analysed together in an internally consistent theoretical and methodological framework. Results show that while cranial shape reflects the population history differences between Mesolithic and Neolithic lineages, relative limb dimensions exhibit significant congruence with environmental variables such as latitude and temperature, even after controlling for geography and time. Also, overall limb size is found to be consistently larger in hunter–gatherers than farmers, suggesting a reduction in size related to factors other than thermoregulatory adaptation. Therefore, our results suggest that relative limb dimensions are not tracking the same demographic population history as the cranium, and point to the strong influence of climatic, dietary and behavioural factors in determining limb morphology, irrespective of underlying neutral demographic processes.     

Recent origin and cultural reversion of a hunter-gatherer group

Contemporary hunter–gatherer groups are often thought to serve as models of an ancient lifestyle that was typical of human populations prior to the development of agriculture. Patterns of genetic variation in hunter–gatherer groups such as the !Kung and African Pygmies are consistent with this view, as they exhibit low genetic diversity coupled with high frequencies of divergent mtDNA types not found in surrounding agricultural groups, suggesting long-term isolation and small population sizes. We report here genetic evidence concerning the origins of the Mlabri, an enigmatic hunter–gatherer group from northern Thailand. The Mlabri have no mtDNA diversity, and the genetic diversity at Y-chromosome and autosomal loci are also extraordinarily reduced in the Mlabri. Genetic, linguistic, and cultural data all suggest that the Mlabri were recently founded, 500–800 y ago, from a very small number of individuals. Moreover, the Mlabri appear to have originated from an agricultural group and then adopted a hunting–gathering subsistence mode. This example of cultural reversion from agriculture to a hunting–gathering lifestyle indicates that contemporary hunter–gatherer groups do not necessarily reflect a pre-agricultural lifestyle.     

An early divergence of KhoeSan ancestors from those of other modern humans is supported by an ABC-based analysis of autosomal resequencing data

Sub-Saharan Africa has consistently been shown to be the most genetically diverse region in the world. Despite the fact that a substantial portion of this variation is partitioned between groups practicing a variety of subsistence strategies and speaking diverse languages, there is currently no consensus on the genetic relationships of sub-Saharan African populations. San (a subgroup of KhoeSan) and many Pygmy groups maintain hunter-gatherer lifestyles and cluster together in autosomal-based analysis, whereas non-Pygmy Niger-Kordofanian speakers (non-Pygmy NKs) predominantly practice agriculture and show substantial genetic homogeneity despite their wide geographic range throughout sub-Saharan Africa. However, KhoeSan, who speak a set of relatively unique click-based languages, have long been thought to be an early branch of anatomically modern humans based on phylogenetic analysis. To formally test models of divergence among the ancestors of modern African populations, we resequenced a sample of San, Eastern, and Western Pygmies and non-Pygmy NKs individuals at 40 nongenic (～2 kb) regions and then analyzed these data within an Approximate Bayesian Computation (ABC) framework. We find substantial support for a model of an early divergence of KhoeSan ancestors from a proto-Pygmy-non-Pygmy NKs group ～110 thousand years ago over a model incorporating a proto-KhoeSan-Pygmy hunter-gatherer divergence from the ancestors of non-Pygmy NKs. The results of our analyses are consistent with previously identified signals of a strong bottleneck in Mbuti Pygmies and a relatively recent expansion of non-Pygmy NKs. We also develop a number of methodologies that utilize "pseudo-observed" data sets to optimize our ABC-based inference. This approach is likely to prove to be an invaluable tool for demographic inference using genome-wide resequencing data.     

Why are population growth rate estimates of past and present hunter–gatherers so different?

Hunter–gatherer population growth rate estimates extracted from archaeological proxies and ethnographic data show remarkable differences, as archaeological estimates are orders of magnitude smaller than ethnographic and historical estimates. This could imply that prehistoric hunter–gatherers were demographically different from recent hunter–gatherers. However, we show that the resolution of archaeological human population proxies is not sufficiently high to detect actual population dynamics and growth rates that can be observed in the historical and ethnographic data. We argue that archaeological and ethnographic population growth rates measure different things; therefore, they are not directly comparable. While ethnographic growth rate estimates of hunter–gatherer populations are directly linked to underlying demographic parameters, archaeological estimates track changes in the long-term mean population size, which reflects changes in the environmental productivity that provide the ultimate constraint for forager population growth. We further argue that because of this constraining effect, hunter–gatherer populations cannot exhibit long-term growth independently of increasing environmental productivity.This article is part of the theme issue ‘Cross-disciplinary approaches to prehistoric demography’.     

Geography predicts neutral genetic diversity of human populations

A leading theory for the origin of modern humans, the ‘recent African origin’ (RAO) model [1], postulates that the ancestors of all modern humans originated in East Africa and that, around 100,000 years ago, some modern humans left the African continent and subsequently colonised the entire world, displacing previously established human species such as Neanderthals in Europe 2., 3.. This scenario is supported by the observation that human populations from Africa are genetically the most diverse [2] and that the genetic diversity of non-African populations is negatively correlated with their genetic differentiation towards populations from Africa [3].     

Later Stone Age human hair from Vaalkrans Shelter,Cape Floristic Region of South Africa,reveals genetic affinity to Khoe groups

Previous studies show that the indigenous people of the southern Cape of South Africa were dramatically impacted by the arrival of European colonists starting ~400 years ago and their descendants are today mixed with Europeans and Asians. To gain insight on the occupants of the Vaalkrans Shelter located at the southernmost tip of Africa, we investigated the genetic make-up of an individual who lived there about 200 years ago. We further contextualize the genetic ancestry of this individual among prehistoric and current groups. From a hair sample excavated at the shelter, which was indirectly dated to about 200 years old, we sequenced the genome (1.01 times coverage) of a Later Stone Age individual. We analyzed the Vaalkrans genome together with genetic data from 10 ancient (pre-colonial) individuals from southern Africa spanning the last 2000 years. We show that the individual from Vaalkrans was a man who traced ~80% of his ancestry to local southern San hunter–gatherers and ~20% to a mixed East African-Eurasian source. This genetic make-up is similar to modern-day Khoekhoe individuals from the Northern Cape Province (South Africa) and Namibia, but in the southern Cape, the Vaalkrans man's descendants have likely been assimilated into mixed-ancestry “Coloured” groups. The Vaalkrans man's genome reveals that Khoekhoe pastoralist groups/individuals lived in the southern Cape as late as 200 years ago, without mixing with non-African colonists or Bantu-speaking farmers. Our findings are also consistent with the model of a Holocene pastoralist migration, originating in Eastern Africa, shaping the genomic landscape of historic and current southern African populations.     

The First Modern Human Dispersals across Africa

The emergence of more refined chronologies for climate change and archaeology in prehistoric Africa, and for the evolution of human mitochondrial DNA (mtDNA), now make it feasible to test more sophisticated models of early modern human dispersals suggested by mtDNA distributions. Here we have generated 42 novel whole-mtDNA genomes belonging to haplogroup L0, the most divergent clade in the maternal line of descent, and analysed them alongside the growing database of African lineages belonging to L0’s sister clade, L1’6. We propose that the last common ancestor of modern human mtDNAs (carried by “mitochondrial Eve”) possibly arose in central Africa ~180 ka, at a time of low population size. By ~130 ka two distinct groups of anatomically modern humans co-existed in Africa: broadly, the ancestors of many modern-day Khoe and San populations in the south and a second central/eastern African group that includes the ancestors of most extant worldwide populations. Early modern human dispersals correlate with climate changes, particularly the tropical African “megadroughts” of MIS 5 (marine isotope stage 5, 135–75 ka) which paradoxically may have facilitated expansions in central and eastern Africa, ultimately triggering the dispersal out of Africa of people carrying haplogroup L3 ~60 ka. Two south to east migrations are discernible within haplogroup LO. One, between 120 and 75 ka, represents the first unambiguous long-range modern human dispersal detected by mtDNA and might have allowed the dispersal of several markers of modernity. A second one, within the last 20 ka signalled by L0d, may have been responsible for the spread of southern click-consonant languages to eastern Africa, contrary to the view that these eastern examples constitute relicts of an ancient, much wider distribution.     

Comparative rates of violence in chimpanzees and humans

This paper tests the proposal that chimpanzees (Pan troglodytes) and humans have similar rates of death from intraspecific aggression, whereas chimpanzees have higher rates of non-lethal physical attack (Boehm 1999, Hierarchy in the forest: the evolution of egalitarian behavior. Harvard University Press). First, we assembled data on lethal aggression from long-term studies of nine communities of chimpanzees living in five populations. We calculated rates of death from intraspecific aggression both within and between communities. Variation among communities in mortality rates from aggression was high, and rates of death from intercommunity and intracommunity aggression were not correlated. Estimates for average rates of lethal violence for chimpanzees proved to be similar to average rates for subsistence societies of hunter–gatherers and farmers. Second, we compared rates of non-lethal physical aggression for two populations of chimpanzees and one population of recently settled hunter–gatherers. Chimpanzees had rates of aggression between two and three orders of magnitude higher than humans. These preliminary data support Boehms hypothesis.     

Bushmeat hunting changes regeneration of African rainforests

To assess ecological consequences of bushmeat hunting in African lowland rainforests, we compared paired sites, with high and low hunting pressure, in three areas of southeastern Nigeria. In hunted sites, populations of important seed dispersers—both small and large primates (including the Cross River gorilla, Gorilla gorilla diehli)—were drastically reduced. Large rodents were more abundant in hunted sites, even though they are hunted. Hunted and protected sites had similar mature tree communities dominated by primate-dispersed species. In protected sites, seedling communities were similar in composition to the mature trees, but in hunted sites species with other dispersal modes dominated among seedlings. Seedlings emerging 1 year after clearing of all vegetation in experimental plots showed a similar pattern to the standing seedlings. This study thus verifies the transforming effects of bushmeat hunting on plant communities of tropical forests and is one of the first studies to do so for the African continent.     

Ethiopian genetic diversity reveals linguistic stratification and complex influences on the Ethiopian gene pool

Humans and their ancestors have traversed the Ethiopian landscape for millions of years, and present-day Ethiopians show great cultural, linguistic, and historical diversity, which makes them essential for understanding African variability and human origins. We genotyped 235 individuals from ten Ethiopian and two neighboring (South Sudanese and Somali) populations on an Illumina Omni 1M chip. Genotypes were compared with published data from several African and non-African populations. Principal-component and STRUCTURE-like analyses confirmed substantial genetic diversity both within and between populations, and revealed a match between genetic data and linguistic affiliation. Using comparisons with African and non-African reference samples in 40-SNP genomic windows, we identified "African" and "non-African" haplotypic components for each Ethiopian individual. The non-African component, which includes the SLC24A5 allele associated with light skin pigmentation in Europeans, may represent gene flow into Africa, which we estimate to have occurred ~3 thousand years ago (kya). The non-African component was found to be more similar to populations inhabiting the Levant rather than the Arabian Peninsula, but the principal route for the expansion out of Africa ~60 kya remains unresolved. Linkage-disequilibrium decay with genomic distance was less rapid in both the whole genome and the African component than in southern African samples, suggesting a less ancient history for Ethiopian populations.     

Risk,mobility or population size? Drivers of technological richness among contact-period western North American hunter–gatherers

Identifying factors that influence technological evolution in small-scale societies is important for understanding human evolution. There have been a number of attempts to identify factors that influence the evolution of food-getting technology, but little work has examined the factors that affect the evolution of other technologies. Here, we focus on variation in technological richness (total number of material items and techniques) among recent hunter–gatherers from western North America and test three hypotheses: (i) technological richness is affected by environmental risk, (ii) population size is the primary determinant of technological richness, and (iii) technological richness is constrained by residential mobility. We found technological richness to be correlated with a proxy for environmental risk—mean rainfall for the driest month—in the manner predicted by the risk hypothesis. Support for the hypothesis persisted when we controlled for shared history and intergroup contact. We found no evidence that technological richness is affected by population size or residential mobility. These results have important implications for unravelling the complexities of technological evolution.     

Voice pitch alters mate-choice-relevant perception in hunter–gatherers

In humans, voice pitch is thought to be a cue of underlying quality and an important criterion for mate choice, but data from non-Western cultures have not been provided. Here we test attributions to and preferences for voices with raised and lowered pitch in hunter–gatherers. Using a forced-choice playback experiment, we found that both men and women viewed lower pitched voices in the opposite sex as being better at acquiring resources (e.g. hunting and gathering). While men preferred higher pitched women''s voices as marriage partners, women showed no overall preference for voice pitch in men. However, women who were currently breastfeeding had stronger preferences for higher pitched male voices whereas women not currently breastfeeding preferred lower pitched voices. As testosterone is considered a costly signal associated with dominance, heritable immunity to infection and low paternal investment, women''s preferences potentially reflect a trade-off between securing good genes and paternal investment. Men''s preferences for higher pitched female voices are probably due to an evolved preference for markers of fecundity, reflected in voice pitch.     

African rainforests: past,present and future

The rainforests are the great green heart of Africa, and present a unique combination of ecological, climatic and human interactions. In this synthesis paper, we review the past and present state processes of change in African rainforests, and explore the challenges and opportunities for maintaining a viable future for these biomes. We draw in particular on the insights and new analyses emerging from the Theme Issue on ‘African rainforests: past, present and future’ of Philosophical Transactions of the Royal Society B. A combination of features characterize the African rainforest biome, including a history of climate variation; forest expansion and retreat; a long history of human interaction with the biome; a relatively low plant species diversity but large tree biomass; a historically exceptionally high animal biomass that is now being severely hunted down; the dominance of selective logging; small-scale farming and bushmeat hunting as the major forms of direct human pressure; and, in Central Africa, the particular context of mineral- and oil-driven economies that have resulted in unusually low rates of deforestation and agricultural activity. We conclude by discussing how this combination of factors influences the prospects for African forests in the twenty-first century.     

Complete mitochondrial genomes reveal neolithic expansion into Europe

The Neolithic transition from hunting and gathering to farming and cattle breeding marks one of the most drastic cultural changes in European prehistory. Short stretches of ancient mitochondrial DNA (mtDNA) from skeletons of pre-Neolithic hunter-gatherers as well as early Neolithic farmers support the demic diffusion model where a migration of early farmers from the Near East and a replacement of pre-Neolithic hunter-gatherers are largely responsible for cultural innovation and changes in subsistence strategies during the Neolithic revolution in Europe. In order to test if a signal of population expansion is still present in modern European mitochondrial DNA, we analyzed a comprehensive dataset of 1,151 complete mtDNAs from present-day Europeans. Relying upon ancient DNA data from previous investigations, we identified mtDNA haplogroups that are typical for early farmers and hunter-gatherers, namely H and U respectively. Bayesian skyline coalescence estimates were then used on subsets of complete mtDNAs from modern populations to look for signals of past population expansions. Our analyses revealed a population expansion between 15,000 and 10,000 years before present (YBP) in mtDNAs typical for hunters and gatherers, with a decline between 10,000 and 5,000 YBP. These corresponded to an analogous population increase approximately 9,000 YBP for mtDNAs typical of early farmers. The observed changes over time suggest that the spread of agriculture in Europe involved the expansion of farming populations into Europe followed by the eventual assimilation of resident hunter-gatherers. Our data show that contemporary mtDNA datasets can be used to study ancient population history if only limited ancient genetic data is available.     

Genetic variation reveals large-scale population expansion and migration during the expansion of Bantu-speaking peoples

The majority of sub-Saharan Africans today speak a number of closely related languages collectively referred to as ‘Bantu’ languages. The current distribution of Bantu-speaking populations has been found to largely be a consequence of the movement of people rather than a diffusion of language alone. Linguistic and single marker genetic studies have generated various hypotheses regarding the timing and the routes of the Bantu expansion, but these hypotheses have not been thoroughly investigated. In this study, we re-analysed microsatellite markers typed for large number of African populations that—owing to their fast mutation rates—capture signatures of recent population history. We confirm the spread of west African people across most of sub-Saharan Africa and estimated the expansion of Bantu-speaking groups, using a Bayesian approach, to around 5600 years ago. We tested four different divergence models for Bantu-speaking populations with a distribution comprising three geographical regions in Africa. We found that the most likely model for the movement of the eastern branch of Bantu-speakers involves migration of Bantu-speaking groups to the east followed by migration to the south. This model, however, is only marginally more likely than other models, which might indicate direct movement from the west and/or significant gene flow with the western Branch of Bantu-speakers. Our study use multi-loci genetic data to explicitly investigate the timing and mode of the Bantu expansion and it demonstrates that west African groups rapidly expanded both in numbers and over a large geographical area, affirming the fact that the Bantu expansion was one of the most dramatic demographic events in human history.