The First Modern Human Dispersals across Africa

Decision letter: Admixture into and within sub-Saharan Africa

The various genetic systems (mitochondrial DNA, the Y-chromosome and the genome-wide autosomes) indicate that Africa is the most genetically diverse continent in the world and the most likely place of origin for anatomically modern humans. However, where in Africa modern humans arose and how the current genetic makeup within the continent was shaped is still open to debate. Here, we summarize the debate and focus especially on the maternally inherited mitochondrial DNA (mtDNA) and a recently revised chronology for the African mtDNA tree. We discuss the possible origin of modern humans in southern, eastern or Central Africa; the possibility of a migration from southern to eastern Africa more than 100 ka, carrying lineages within mtDNA haplogroup L0; the evidence for a climate-change-mediated population expansion in eastern Africa involving mtDNA haplogroup L3, leading to the “out-of-Africa” migration around 70–60 ka; the re-population of North Africa from the Near East around 40–30 ka suggested by mtDNA haplogroups U6 and M1; the evidence for population expansions and dispersals across the continent at the onset of the Holocene; and the impact of the Bantu dispersals in Central, eastern and southern Africa within the last few millennia.

In recent years, new evidence for the early use of plant foods has challenged the stereotype of the meat-eating Paleolithic. Whilst often making up the smaller component of the diet, plant foods are key to hominin diets, carbohydrates especially providing an efficient energy resource. This paper reviews the current evidence for the role of plant foods in the evolution and dispersal of early modern humans and our closest ancestors, with a focus on new evidence for early diet from Island Southeast Asia, Australia and New Guinea. It demonstrates the importance of plant foods and their processing, to the dietary flexibility and adaptive capacity of our species.

We extend the continuity of microblade technology in the Indian Subcontinent to 45 ka, on the basis of optical dating of microblade assemblages from the site of Mehtakheri, (22° 13' 44″ N Lat 76° 01' 36″ E Long) in Madhya Pradesh, India. Microblade technology in the Indian Subcontinent is continuously present from its first appearance until the Iron Age (~3 ka), making its association with modern humans undisputed. It has been suggested that microblade technology in the Indian Subcontinent was developed locally by modern humans after 35 ka. The dates reported here from Mehtakheri show this inference to be untenable and suggest alternatively that this technology arrived in the Indian Subcontinent with the earliest modern humans. It also shows that modern humans in Indian Subcontinent and SE Asia were associated with differing technologies and this calls into question the “southern dispersal” route of modern humans from Africa through India to SE Asia and then to Australia. We suggest that modern humans dispersed from Africa in two stages coinciding with the warmer interglacial conditions of MIS 5 and MIS 3. Competitive interactions between African modern humans and Indian archaics who shared an adaptation to tropical environments differed from that between modern humans and archaics like Neanderthals and Denisovans, who were adapted to temperate environments. Thus, while modern humans expanded into temperate regions during warmer climates, their expansion into tropical regions, like the Indian Subcontinent, in competition with similarly adapted populations, occurred during arid climates. Thus modern humans probably entered the Indian Subcontinent during the arid climate of MIS 4 coinciding with their disappearance from the Middle East and Northern Africa. The out of phase expansion of modern humans into tropical versus temperate regions has been one of the factors affecting the dispersal of modern humans from Africa during the period 200–40 ka.

Discovery of the Fuyan teeth: challenging or complementing the out-of-Africa scenario?

The earliest anatomically modern humans in Europe are thought to have appeared around 43,000-42,000 calendar years before present (43-42 kyr cal BP), by association with Aurignacian sites and lithic assemblages assumed to have been made by modern humans rather than by Neanderthals. However, the actual physical evidence for modern humans is extremely rare, and direct dates reach no farther back than about 41-39 kyr cal BP, leaving a gap. Here we show, using stratigraphic, chronological and archaeological data, that a fragment of human maxilla from the Kent's Cavern site, UK, dates to the earlier period. The maxilla (KC4), which was excavated in 1927, was initially diagnosed as Upper Palaeolithic modern human. In 1989, it was directly radiocarbon dated by accelerator mass spectrometry to 36.4-34.7 kyr cal BP. Using a Bayesian analysis of new ultrafiltered bone collagen dates in an ordered stratigraphic sequence at the site, we show that this date is a considerable underestimate. Instead, KC4 dates to 44.2-41.5 kyr cal BP. This makes it older than any other equivalently dated modern human specimen and directly contemporary with the latest European Neanderthals, thus making its taxonomic attribution crucial. We also show that in 13 dental traits KC4 possesses modern human rather than Neanderthal characteristics; three other traits show Neanderthal affinities and a further seven are ambiguous. KC4 therefore represents the oldest known anatomically modern human fossil in northwestern Europe, fills a key gap between the earliest dated Aurignacian remains and the earliest human skeletal remains, and demonstrates the wide and rapid dispersal of early modern humans across Europe more than 40 kyr ago.

A review of late quaternary pollen studies in East, Central and Southern Africa

Acquired immune deficiency syndrome (AIDS) is worldwide, but the clinical and epidemiological pattern of the disease in Africa is different from that in developed areas. "Type 1 AIDS" occurs in industrialized North America and Europe; it has a distinctive sex ratio (16:1) and risk pattern of IV drug use and sexual practices. "Type 2 AIDS" occurs in Third World countries, particularly in eastern, southern, and central Africa. It is characterized by an entirely different sex ratio (1:1) and by distinctively different risk patterns. Both epidemics are caused by the HIV-1 virus. The key concept for understanding the origins of the differences between Type 1 and Type 2 AIDS is the migratory labor system in eastern, central, and southern Africa. This system causes long absences, increased family breakdown, and increased numbers of sexual partners. Historically the organization of this labor market has created a population which suffers from epidemics of sexually transmitted diseases. These historical patterns are presented as evidence for the contemporary transmission of AIDS. When contemporary AIDS and HIV-1 seropositivity prevalence data are examined, a systematic temporal and geographic pattern emerges for the AIDS epidemic in Africa. Despite a paucity of good data, the prevalence data from eastern, central, and southern Africa support the thesis of migrant labor's role in the transmission of AIDS.

Dispersals Out of Africa and Back to Africa: Modern origins in North Africa

In the recent decades, East African region has been attracting more inflows of Foreign Direct Investment (FDI) than Central Africa, while the trend was different for the period before 1990. This study aimed at identifying factors that determine FDI attraction in the two regions using a panel data of six countries (three in Central Africa and other three in East Africa) over the year 1990-2018. We applied the Panel Autoregressive Distributed Lag (P-ARDL) model based on the Pooled Mean Group (PMG) estimation to capture short and long-run relationships amongst variables. Results indicated that in the long-run, infrastructure quality, trade openness and market size explain the attraction of FDI inflows in both Central and East Africa. A comparison of the two regions shows a sharp contrast of factors that attract FDI. While trade openness and natural resources endowment are key factors for Central Africa, infrastructure quality and market size are critical in East Africa. However, resource curse hypothesis has been found in Central Africa since the increase in resource rents decreases the attraction of FDI inflows. Therefore, policies which promote cooperation among countries by increasing the levels of trade, reduce the costs of doing business and invest in infrastructures should be implemented in the two regions.

East Africa, the region where Merrick Posnansky started his professional career, has long been accepted as the major centre for the study of the origins of hominids and their technological systems. Recently, human geneticists and some palaeoanthropologists have also proposed an African origin for anatomically modern humans (Homo sapiens sapiens), although much of the proof cited is from non-African sources — mainly Europe and the Middle East. Fortunately these models have stimulated reassessment of the sub-Saharan Middle Stone Age (MSA), the archaeological phase between 200,000 and 30,000 years ago which represents the beginnings of regional variation in technology and cultural adaptation as well as the period in which modern humans appeared. Long ignored by East African archaeologists in favour of the earliest cultural record, or, at the other extreme, Neolithic and Iron Age research, the MSA is critical to the evaluation of models of the emergence of our own species. This paper reviews the current arguments concerning the origin and dispersal of modern humans, and the importance of the MSA for the resolution of the problem. It also describes the results from a 1990 survey for MSA sites conducted in southwestern Tanzania within the framework of these current models.

This paper analyzed the factors that drive foreign direct investments (FDI) by looking at regional heterogeneity among the five African regions. For the first time, FDI drivers are analyzed for each of the five regions of Africa contrary to previous studies which focused on Africa as a whole. The paper used a panel dataset from 1970 to 2010 of 53 African countries divided into: Central, East, North, Southern, and West Africa. Ordinary least squares (OLS) and generalized method of moments (GMM) techniques are used for the estimations. The main results indicate that: (i) agglomeration has a strong positive relationship with FDI inflows in all the regions except Central Africa. However, in West Africa, the second lag of FDI is significantly negative; (ii) there is a negative relationship between FDI inflows and GDP per capita in all the five regions, but a U‐shaped relationship is observed in Central, North, and West Africa. But GDP growth rate has a strongly positive relationship with FDI inflows in Central Africa but negatively significant in West Africa; (iii) FDI follows domestic investment in East, Southern, and West Africa; (iv) democracy is a major factor in attracting FDI to Southern Africa, being upward concave; (v) infrastructure development has a positive impact on FDI inflows in East and North Africa; (vi) trade openness has a positive relationship with FDI inflows in all the five regions except in East Africa; (vii) inflation deters FDI inflows to East Africa; (viii) the level of urbanization has a strong positive relationship with FDI inflows only in West Africa; (ix) net foreign aid has a negative relationship with FDI inflows to East, North, and Southern Africa; (x) higher life expectancy deters FDI inflows to Central Africa but promotes the same to East and North Africa; (xi) metal production and exportation attract significant FDI to Central Africa while oil production and exportation attract higher FDI to West Africa; (xii) monetary union attracts greater FDI to Central and West Africa; and (xiii) political instability is a strong hindrance to FDI inflows to West Africa.

The origins of our species, modern humans, have long been a contentious issue, with numerous models based on fossil and archaeological data having been proposed and argued about. Beginning 30 years ago, with seminal studies of mitochondrial DNA variation, genetic and now genomic data have firmly established that Africa is the home of modern humans, and that all non-African populations are derived from Africa. Moreover, the analysis of genomic data from archaic human fossils has revealed that interbreeding occurred between modern and archaic humans. Thus, the model that best describes the origins of our species is that of a recent African origin followed by assimilation of archaic humans as modern humans dispersed across and out of Africa. However, numerous questions remain, particularly whether there was a single dispersal or multiple dispersals of modern humans from Africa, and genomic data bring insights into this question.

The complicated origins of our species

Although fossil remains show that anatomically modern humans dispersed out of Africa into the Near East ∼100 to 130 ka, genetic evidence from extant populations has suggested that non-Africans descend primarily from a single successful later migration. Within the human mitochondrial DNA (mtDNA) tree, haplogroup L3 encompasses not only many sub-Saharan Africans but also all ancient non-African lineages, and its age therefore provides an upper bound for the dispersal out of Africa. An analysis of 369 complete African L3 sequences places this maximum at ∼70 ka, virtually ruling out a successful exit before 74 ka, the date of the Toba volcanic supereruption in Sumatra. The similarity of the age of L3 to its two non-African daughter haplogroups, M and N, suggests that the same process was likely responsible for both the L3 expansion in Eastern Africa and the dispersal of a small group of modern humans out of Africa to settle the rest of the world. The timing of the expansion of L3 suggests a link to improved climatic conditions after ∼70 ka in Eastern and Central Africa rather than to symbolically mediated behavior, which evidently arose considerably earlier. The L3 mtDNA pool within Africa suggests a migration from Eastern Africa to Central Africa ∼60 to 35 ka and major migrations in the immediate postglacial again linked to climate. The largest population size increase seen in the L3 data is 3-4 ka in Central Africa, corresponding to Bantu expansions, leading diverse L3 lineages to spread into Eastern and Southern Africa in the last 3-2 ka.