Aeta woman (Philippines) – Wikipedia (Ken Llio)
Modern humans pushed out of Africa along two routes: a northern one through the Levant and into Europe and a southern one along the Indian Ocean coast and eventually into New Guinea and Australia. The southern route is said to have had two waves: an earlier one between 62,000 and 75,000 years ago that was ancestral to present-day Australian Aborigines and a later one between 25,000 and 38,000 years ago that was ancestral to present-day Negrito groups in Southeast Asia: the Andaman Islanders, the Semang of the Malayan Peninsula, and the Aeta of the Philippines, although these groups would have intermixed with the population already present from the first wave (Rasmussen et al. 2011; Reyes-Centeno et al. 2014).
Did this southern route end in Southeast Asia or did it swing north along the Pacific coast? We know that the Philippines was once inhabited by Negritos—the country still has over thirty such groups. In addition, there have been claims that a Negrito group used to live on Taiwan. In the early 20th century, the anthropologist Rolange Dixon argued that a Negrito population once occupied the whole of the South, Southeast, and East Asian littoral:
In the late 20th century, interest declined in Negritos and their place in human prehistory, partly because anthropologists were increasingly taking an ahistorical approach hunter-gatherers and shunning anything that smacked of racial or evolutionary thinking. Though a student of Franz Boas, Dixon studied anthropology (1897-1906) at a time when Boas believed not only in the existence of human races but also in psychological differences between them, albeit in a statistical sense (Frost 2014, Frost 2015). Furthermore, genetic studies in the late 20th century seemed to show that different Negrito groups had little in common with each other. Clearly, Negritos are a very ancient population, and the time to the most recent ancestor for all of them is greater than it is for, say, present-day Europeans and present-day East Asians. They still look similar to each other only because they remained under similar climatic and cultural conditions.
At this time the southern and eastern borderlands, from India around to Kamchatka, seem to have been occupied in the main by a dolichocephalic, dark-skinned, Negroid population which was a blend in varying proportions of the Proto-Australoid and Proto-Negroid types. There is some evidence which leads us to believe that this Negroid population extended farther westward than India, along the shores of the Persian Gulf and the southern coast of Arabia, so being continuous with the great area held by similar peoples in Africa. (Dixon 1923, p. 243)
In the late 20th century, interest declined in Negritos and their place in human prehistory, partly because anthropologists were increasingly taking an ahistorical approach hunter-gatherers and shunning anything that smacked of racial or evolutionary thinking. Though a student of Franz Boas, Dixon studied anthropology (1897-1906) at a time when Boas believed not only in the existence of human races but also in psychological differences between them, albeit in a statistical sense (Frost 2014, Frost 2015). Furthermore, genetic studies in the late 20th century seemed to show that different Negrito groups had little in common with each other. Clearly, Negritos are a very ancient population, and the time to the most recent ancestor for all of them is greater than it is for, say, present-day Europeans and present-day East Asians. They still look similar to each other only because they remained under similar climatic and cultural conditions.
Recent years have seen a renewal of interest in Negritos. Mitochondrial DNA studies have shown that they are indeed the remnants of a southern "Out of Africa" route, together with New Guineans and Australian Aborigines (Reyes-Centeno et al. 2014; Stoneking and Delfin 2010; Thangaraj et al. 2005). Of particular interest is the discovery of significant admixture from these peoples in Amerindians from Amazonia and the Central Brazilian Plateau (Skoglund et al. 2015). This admixture seems to be very old:
As the authors note, this finding is consistent with ancient skeletal remains from the same region:
The genetic data allow us to say with confidence that Population Y ancestry arrived south of the ice sheets anciently: the fact that the geographically diverse Andamanese, Australian and New Guinean populations are all similarly related to this source suggests that the population is no longer extant, and the absence of long-range admixture linkage disequilibrium suggests that the population mixture did not occur in the last few thousand years.
As the authors note, this finding is consistent with ancient skeletal remains from the same region:
This discovery is striking in light of interpretations of the morphology of some early Native American skeletons, which some authors have suggested have affinities to Australasian groups. The largest number of skeletons that have been described as having this craniofacial morphology and that date to younger than ten thousand years have been found in Brazil6, the home of the Suruí, Karitiana and Xavante who in genetic data show the strongest affinity to Australasians.
How did this population reach the Amazonian basin? Perhaps the same way the Paleo-Amerindians did: across the Bering Strait and down through North America. If Negrito groups had reached south China and the Philippines, they could have continued up the East Asian shoreline and then down the west coast of North America. One problem with this model, raised by Greg Cochran and Steve Sailer, is that the "Australasian" admixture is absent from native North Americans. Keep in mind, however, that at least three waves of migration entered North America: the latest one corresponding to the Inuit-Aleut peoples, an earlier one corresponding to the Na-Dene peoples, and the earliest one corresponding to all other Amerindian groups. Only this earliest wave reached South America. There has consequently been much more population replacement among native North Americans than among native South Americans.
Population replacement is widely seen as something that has been done by European peoples (and, more recently, which is being done to them). In reality, the world was not a static place before Columbus. Human populations have been replacing each other for a very long time.
References
Cochran, G. (2018). Beringians, West Hunter, January 4
Dixon, R.B. (1923). The Racial History of Man, New York: Charles Scribner's Sons.
Frost, P. (2014). The Franz Boas you never knew, Evo and Proud, July 13 http://evoandproud.blogspot.ca/2014/07/the-franz-boas-you-never-knew.html
Frost, P. (2015). More on the younger Franz Boas, Evo and Proud, April 18
Rasmussen M, et al. (2011) An Aboriginal Australian genome reveals separate human dispersals into Asia, Science, 334(6052), 94-98.
Reyes-Centeno, H., S. Ghirotto, F. Détroit, D. Grimaud-Hervé, G. Barbujani, and K. Harvati. (2014). Genomic and cranial phenotype data support multiple modern human dispersals from Africa and a southern route into Asia, PNAS, 111(20), 7248-7253.
Sailer, S. (2018). Were There People Already in the New World When the Indians Arrived? The Unz Review, January 6
Skoglund, P., S. Mallick, M.C. Bortolini, N. Chennagiri, T. Hunemeier, M.L. Petzl-Erier, F.M. Salzano, N. Patterson, and D. Reich. (2015). Genetic evidence for two founding populations of the Americas, Nature, 525, 104-108
Stoneking, M. and F. Delfin (2010). The Human Genetic History of East Asia: Weaving a Complex Tapestry, Current Biology, 20(4), R188-R193
Thangaraj, K., G. Chaubey, T. Kivisild, A.G. Reddy, V.K. Singh, et al. (2005). Reconstructing the origin of Andaman Islanders, Science, 308(5724), 996