African human diversity, origins and migrations

The continent of Africa is thought to be the site of origin of all modern humans and is the more recent origin of millions of African Americans. Although Africa has the highest levels of human genetic diversity both within and between populations, it is under-represented in studies of human genetics. Recent advances have been made in understanding the origins of modern humans within Africa, the rate of adaptations due to positive selection, the routes taken in the first migrations of modern humans out of Africa, and the degree of admixture with archaic populations. Africa is also in dire need of effective medical interventions, and studies of genetic variation in Africans will shed light on the genetic basis of diseases and resistance to infectious diseases. Thus, we have tremendous potential to learn about human variation and evolutionary history and to positively impact human health care from studies of genetic diversity in Africa.     

Evolution,revolution or saltation scenario for the emergence of modern cultures?

Crucial questions in the debate on the origin of quintessential human behaviours are whether modern cognition and associated innovations are unique to our species and whether they emerged abruptly, gradually or as the result of a discontinuous process. Three scenarios have been proposed to account for the origin of cultural modernity. The first argues that modern cognition is unique to our species and the consequence of a genetic mutation that took place approximately 50 ka in Africa among already evolved anatomically modern humans. The second posits that cultural modernity emerged gradually in Africa starting at least 200 ka in concert with the origin of our species on that continent. The third states that innovations indicative of modern cognition are not restricted to our species and appear and disappear in Africa and Eurasia between 200 and 40 ka before becoming fully consolidated. We evaluate these scenarios in the light of new evidence from Africa, Asia and Europe and explore the mechanisms that may have led to modern cultures. Such reflections will demonstrate the need for further inquiry into the relationship between climate and demographic/cultural change in order to better understand the mechanisms of cultural transmission at work in Neanderthals and early Homo sapiens populations.     

Signatures of the preagricultural peopling processes in sub-Saharan Africa as revealed by the phylogeography of early Y chromosome lineages

The study of Y chromosome variation has helped reconstruct demographic events associated with the spread of languages, agriculture, and pastoralism in sub-Saharan Africa, but little attention has been given to the early history of the continent. In order to overcome this lack of knowledge, we carried out a phylogeographic analysis of haplogroups A and B in a broad data set of sub-Saharan populations. These two lineages are particularly suitable for this objective because they are the two most deeply rooted branches of the Y chromosome genealogy. Their distribution is almost exclusively restricted to sub-Saharan Africa where their frequency peaks at 65% in groups of foragers. The combined high-resolution single nucleotide polymorphism analysis with short tandem repeats variation of their subclades reveals strong geographic and population structure for both haplogroups. This has allowed us to identify specific lineages related to regional preagricultural dynamics in different areas of sub-Saharan Africa. In addition, we observed signatures of relatively recent contact, both among Pygmies and between them and Khoisan speaker groups from southern Africa, thus contributing to the understanding of the complex evolutionary relationships among African hunter-gatherers. Finally, by revising the phylogeography of the very early human Y chromosome lineages, we have obtained support for the role of southern Africa as a sink, rather than a source, of the first migrations of modern humans from eastern and central parts of the continent. These results open new perspectives on the early history of Homo sapiens in Africa, with particular attention to areas of the continent where human fossil remains and archaeological data are scant.     

Out of Africa with regional interbreeding? Modern human origins

A central issue in paleoanthropology is whether modern humans emerged in a single geographic area and subsequently replaced the preexisting people in other areas. Although the study of human mitochondrial DNAs supported this single-origin and complete-replacement model, a recent paper(1) argues that humans expanded out of Africa more than once and regionally interbred. However, both the genetic antiquity and the impact of the African contribution to modern Homo sapiens are so great as to view Africa as a central place of human evolution. Despite the possibility that out-of-Africa H. sapiens interbred with other populations, this evidence is more consistent with the uniregional hypothesis than the multiregional hypothesis of modern human origins.     

Genomics refutes an exclusively African origin of humans

Ten years ago, evidence from genetics gave strong support to the "recent African origin" view of the evolution of modern humans, which posits that Homo sapiens arose as a new species in Africa and subsequently spread, leading to the extinction of other archaic human species. Subsequent data from the nuclear genome not only fail to support this model, they do not support any simple model of human demographic history. In this paper, we study a process in which the modern human phenotype originates in Africa and then advances across the world by local demic diffusion, hybridization, and natural selection. While the multiregional model of human origins posits a number of independent single locus selective sweeps, and the "out of Africa" model posits a sweep of a new species, we study the intermediate case of a phenotypic sweep. Numerical simulations of this process replicate many of the seemingly contradictory features of the genetic data, and suggest that as much as 80% of nuclear loci have assimilated genetic material from non-African archaic humans.     

Modern human cranial diversity in the Late Pleistocene of Africa and Eurasia: Evidence from Nazlet Khater,Peştera cu Oase,and Hofmeyr

The origin and evolutionary history of modern humans is of considerable interest to paleoanthropologists and geneticists alike. Paleontological evidence suggests that recent humans originated and expanded from an African lineage that may have undergone demographic crises in the Late Pleistocene according to archaeological and genetic data. This would suggest that extant human populations derive from, and perhaps sample a restricted part of the genetic and morphological variation that was present in the Late Pleistocene. Crania that date to Marine Isotope Stage 3 should yield information pertaining to the level of Late Pleistocene human phenotypic diversity and its evolution in modern humans. The Nazlet Khater (NK) and Hofmeyr (HOF) crania from Egypt and South Africa, together with penecontemporaneous specimens from the Pe?tera cu Oase in Romania, permit preliminary assessment of variation among modern humans from geographically disparate regions at this time. Morphometric and morphological comparisons with other Late Pleistocene modern human specimens, and with 23 recent human population samples, reveal that elevated levels of variation are present throughout the Late Pleistocene. Comparison of Holocene and Late Pleistocene craniometric variation through resampling analyses supports hypotheses derived from genetic data suggesting that present phenotypic variation may represent only a restricted part of Late Pleistocene human diversity. The Nazlet Khater, Hofmeyr, and Oase specimens provide a unique glimpse of that diversity. Am J Phys Anthropol, 2009. © 2009 Wiley‐Liss, Inc.     

Modern human origins: progress and prospects

The question of the mode of origin of modern humans (Homo sapiens) has dominated palaeoanthropological debate over the last decade. This review discusses the main models proposed to explain modern human origins, and examines relevant fossil evidence from Eurasia, Africa and Australasia. Archaeological and genetic data are also discussed, as well as problems with the concept of 'modernity' itself. It is concluded that a recent African origin can be supported for H. sapiens, morphologically, behaviourally and genetically, but that more evidence will be needed, both from Africa and elsewhere, before an absolute African origin for our species and its behavioural characteristics can be established and explained.     

An Australasian test of the recent African origin theory using the WLH-50 calvarium

This analysis investigates the ancestry of a single modern human specimen from Australia, WLH-50 (Thorne et al., in preparation; Webb, 1989). Evaluating its ancestry is important to our understanding of modern human origins in Australasia because the prevailing models of human origins make different predictions for the ancestry of this specimen, and others like it. Some authors believe in the validity of a complete replacement theory and propose that modern humans in Australasia descended solely from earlier modern human populations found in Late Pleistocene Africa and the Levant. These ancestral modern populations are believed to have completely replaced other archaic human populations, including the Ngandong hominids of Indonesia. According to this recent African origin theory, the archaic humans from Indonesia are classified as Homo erectus, a different evolutionary species that could not have contributed to the ancestry of modern Australasians. Therefore this theory of complete replacement makes clear predictions concerning the ancestry of the specimen WLH-50. We tested these predictions using two methods: a discriminant analysis of metric data for three samples that are potential ancestors of WLH-50 (Ngandong, Late Pleistocene Africans, Levant hominids from Skhul and Qafzeh) and a pairwise difference analysis of nonmetric data for individuals within these samples. The results of these procedures provide an unambiguous refutation of a model of complete replacement within this region, and indicate that the Ngandong hominids or a population like them may have contributed significantly to the ancestry of WLH-50. We therefore contend that Ngandong hominids should be classified within the evolutionary species, Homo sapiens. The Multiregional model of human evolution has the expectation that Australasian ancestry is in all three of the potentially ancestral groups and best explains modern Australasian origins.     

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].     

Ethnic populations of India as seen from an evolutionary perspective

It is now widely accepted that (i) modern humans,Homo sapiens sapiens, evolved in Africa, (ii) migrated out of Africa and replaced archaic humans in other parts of the world, and (iii) one of the first waves of out-of-Africa migration came into India. India, therefore, served as a major corridor for dispersal of modern humans. By studying variation at DNA level in contemporary human populations of India, we have provided evidence that mitochondrial DNA haplotypes based on RFLPs are strikingly similar across ethnic groups of India, consistent with the hypothesis that a small number of females entered India during the initial process of the peopling of India. We have also provided evidence that there may have been dispersal of humans from India to southeast Asia. In conjunction with haplotype data, nucleotide sequence data of a hypervariable segment (HVS-1) of the mitochondrial genome indicate that the ancestors of the present austro-asiatic tribal populations may have been the most ancient inhabitants of India. Based on Y-chromosomal RFLP and STRP data, we have also been able to trace footprints of human movements from west and central Asia into India.     

A geographically explicit genetic model of worldwide human-settlement history

Currently available genetic and archaeological evidence is generally interpreted as supportive of a recent single origin of modern humans in East Africa. However, this is where the near consensus on human settlement history ends, and considerable uncertainty clouds any more detailed aspect of human colonization history. Here, we present a dynamic genetic model of human settlement history coupled with explicit geographical distances from East Africa, the likely origin of modern humans. We search for the best-supported parameter space by fitting our analytical prediction to genetic data that are based on 52 human populations analyzed at 783 autosomal microsatellite markers. This framework allows us to jointly estimate the key parameters of the expansion of modern humans. Our best estimates suggest an initial expansion of modern humans approximately 56,000 years ago from a small founding population of approximately 1,000 effective individuals. Our model further points to high growth rates in newly colonized habitats. The general fit of the model with the data is excellent. This suggests that coupling analytical genetic models with explicit demography and geography provides a powerful tool for making inferences on human-settlement history.     

Genetics and modern human origins

The past decade has brought considerable debate on the subject of modern human origins. The nature of the transition from Homo erectus to archaic Homo sapiens to modern H. sapiens has been examined primarily in terms of the relative contribution of archaic populations to later moderns, both within and among geographic regions. The recent African origin model proposes that modern humans appeared first in Africa between 100,000 and 200,000 years ago, and then spread through the rest of the Old World, replacing preexisting populations.^1–6 This model has been referred to by a variety of names, including “replacement”, “Garden of Eden”, “Noah's Ark”, and “out of Africa”. The recent African origin model contrasts with the multiregional model, which proposes a species-wide transition to modern humans throughout the Old World during the past million years or more.^7–10 Indeed, some proponents of the multiregional model advocate placing Homo erectus and all subsequent species of Homo in the evolutionary species Homo sapiens.¹¹ This contrasts with the view that there were multiple hominid species during the Middle Pleistocene. The debate continues.^12,13 Although the multiregional model is often portrayed as proposing a simultaneous transition to anatomically modern humans in different geographic regions, it explicitly allows for varying degrees of continuity across time and space.¹⁰ This model, in the broad sense, does not rule out the possibility that modern human morphology appeared first in Africa and then spread through the rest of the Old World through gene flow. However, not all advocates of the multiregional model adhere to this specific subset of the general model.⁹ Comparison of the African and multiregional models is complicated by considering other, less extreme, hypotheses. Some versions of the recent African origin model imply a speciation event associated with the initial origin of modern humans. Another version, which suggests the possibility of some admixture between “moderns” leaving Africa and preexisting “archaics” elsewhere in the Old World,^14,15 is similar to some variants of the multiregional model, which also suggest that modern morphology appeared first in Africa, but involved admixture with other Old World populations.¹⁶ The major difference between these views appears to be the extent of admixture, although the exact level is never specified. A further complication is the possibility that multiple dispersals from Africa produced a more complicated pattern of worldwide variation.¹⁷     

从中国晚期智人颅牙特征看中国现代人起源

本文提供或援引了中国晚期智人头骨的额骨鳞部最突出点位置、颊部骨骼下缘的形状、头骨最宽处位置等特征和铲形门齿等牙齿特征的出现率等的有关数据,并探讨了这些特征系来源于非洲“夏娃”的后裔,还是中国当地更早的人群。所得结论更倾向于后者而不利于前者。中国旧石器时代中期和晚期的文化之间缺乏显然的反差,没有中断的迹象,也是不利于中国现代人起源的替代说的有力佐证。     

Human genome diversity

Human genome diversity studies analyse genetic variation among individuals and between populations in order to understand the origins and evolution of anatomically modern humans (Homo sapiens sapiens). The availability of thousands of DNA polymorphisms (genetic markers) brings analytic power to these studies. Human genome diversity studies have clearly shown that the large part of genetic variability is due to differences among individuals within populations rather than to differences between populations, effectively discrediting a genetic basis of the concept of ‘race’. Evidence from paleontology, archaeology and genetic diversity studies is quite consistent with an African origin of modern humans more than 100 000 years ago. The evidence favors migrations out of African as the source of the original peopling of Asia, Australia, Europe and Oceania. An international program for the scientific analysis of human genome diversity and of human evolution has been developed. The Human Genome Diversity Project (HGDP) aims to collect and preserve biologic samples from hundreds of populations throughout the world, make DNA from these samples available to scientists and distribute to the scientific community the results of DNA typing with hundreds of genetic markers.     

Modern human origins in Australasia: Replacement or evolution?

The controversies surrounding the origins of modern humans have spawned two competing hypotheses, namely Replacement and Multiregional Evolution. The first suggests that modern Homo sapiens evolved first in Africa, as late as 140 ka, and subsequently inhabited the balance of the Old World. Conversely, the second hypothesis posits that modern humans evolved principally from local populations of archaic hominids indigenous to the major regions of the Old World. The hominid mandibular remains (ca. 1 Ma) from Sangiran, central Java, Indonesia, were studied in order to test these hypotheses. Non-metric comparisons were performed between these fossils and aboriginal H. sapiens from Africa and Australia. The Replacement model would be supported by a unique Afro-Australian grouping while Multiregional Evolution would be suggested by a Sangiran-Australasian group which would exclude the modern Africans. These data support the Multiregional Evolution hypothesis in that a plurality (eight) of the seventeen non-metric features link Sangiran to modern Australians, while only three exclusively group the humans from Africa and Australia. These results are suggestive of morphological continuity, which implies the presence of a genetic continuum in Australasia dating back at least one million years.     

Origin of modern humans in East Asia: clues from the Y chromosome

East Asia is one of the most important regions for studying modern human origin and evolution. A lot of efforts have been made to detect the genetic diversity and to reconstruct the evolutionary history of East Asians, especially using Y chromosome genetic data, in recent years. The Y chromosome data supports the African origin of modern humans in East Asia and the later migration to East Asia through the southern tropic coastline route, and then the northward migration occurred, leading to peopling of the main continent. The genetic data of the Y chromosome reflects a clear prehistoric evolution and migration course of East Asians. As well, the Y chromosome data of East Asians provides clues to elucidate modern human origins and evolution in the neighboring regions, i.e. America, Oceania and the Pacific Islands.     

Origin of modern humans in East Asia: clues from the Y chromosome

East Asia is one of the most important regions for studying modern human origin and evolution. A lot of efforts have been made to detect the genetic diversity and to reconstruct the evolutionary history of East Asians, especially using Y chromosome genetic data, in recent years. The Y chromosome data supports the African origin of modern humans in East Asia and the later migration to East Asia through the southern tropic coastline route, and then the northward migration occurred, leading to peopling of the main continent. The genetic data of the Y chromosome reflects a clear prehistoric evolution and migration course of East Asians. As well, the Y chromosome data of East Asians provides clues to elucidate modern human origins and evolution in the neighboring regions, i.e. America, Oceania and the Pacific Islands.     

新证据下的现代人起源模型

解剖结构上的现代人是指具有近圆球形头骨、短而平的面颅、纤细的骨骼等特征的区别于其他古老人类的化石和现今的人群。支持多地区演化模型和支持近期非洲起源模型的学者,在“解剖结构上的现代人”的应用范围方面是不同的,前者以连续演化为基本思想,认为这一名词只包括智人中较进步的类群;而后者以分支系统学思想为基础,认为包括所有智人。分子古生物学研究显示,尼人、丹人和智人在遗传学水平上属于不同的人种。新近的以标本-种群为单元的系统分析,因为不是以属、种等分类学阶元进行的,因此与分类学的阶元划分无关。该系统分析的结果显示智人属于单系类群,哈尔滨人、大荔人等组成其姊妹群。尼人与智人的分异早于1百万年,与基因组水平的谱系分析相符合。多次多向的穿梭扩散是统计学上符合系统关系的模型。     

Postcranial remains and the origin of modern humans

The nature, timing, and location of the origin of modern humans has been the subject of intense controversy for the last 15 years.^1–4 Genetic data and new radiometric dates for key fossils that lie beyond the range of radiocarbon dating have substantially added to the knowledge derived from the fossil evidence documenting the transition from archaic to modern humans. These new data, however, have failed to resolve the problem in its entirety. Most authorities now accept that Africa played an important, and probably central, role in the origin of modern humans.^7–13 The genetic evidence seems to be particularly emphatic that an African population that existed between 200,000 and 100,000 years ago (100 ka) is ancestral to all living humans.^6,7 Controversy still surrounds the question of how much, if at all, archaic humans from outside of Africa, such as Neandertals, late archaic Chinese hominins such as Jinniushan, and the Indonesian Ngandong hominins, may have contributed to the morphological and genetic diversity present in living populations and the morphology of the earliest fossils of modern humans.¹⁰     

Genes encoding longevity: from model organisms to humans

Ample evidence from model organisms has indicated that subtle variation in genes can dramatically influence lifespan. The key genes and molecular pathways that have been identified so far encode for metabolism, maintenance and repair mechanisms that minimize age-related accumulation of permanent damage. Here, we describe the evolutionary conserved genes that are involved in lifespan regulation of model organisms and humans, and explore the reasons of discrepancies that exist between the results found in the various species. In general, the accumulated data have revealed that when moving up the evolutionary ladder, together with an increase of genome complexity, the impact of candidate genes on lifespan becomes smaller. The presence of genetic networks makes it more likely to expect impact of variation in several interacting genes to affect lifespan in humans. Extrapolation of findings from experimental models to humans is further complicated as phenotypes are critically dependent on the setting in which genes are expressed, while laboratory conditions and modern environments are markedly dissimilar. Finally, currently used methodologies may have only little power and validity to reveal genetic variation in the population. In conclusion, although the study of model organisms has revealed potential candidate genetic mechanisms determining aging and lifespan, to what extent they explain variation in human populations is still uncertain.