A recent report in BMC Biology indicates that modern humans first arrived in southern East Asia 60,000 years ago and settled the rest of East Asia from there. This early date and migration route has significant implications for our understanding of the origins of present-day human populations.
Studies of human origins have witnessed a radical transition from studies based on morphological comparisons to a reliance on molecular genetics. One of the first molecular comparisons estimated human divergence from the African apes at a now generally accepted timescale of 5 million years ago, when most paleontologists then placed it between 15 and 30 million years ago. Later, measurement of genetic diversity revealed the relatively recent origin in Africa of modern humans, who then spread over the entire globe (see  and citations therein). Much current research in anthropology centers on understanding the timing and migration routes of modern humans. An analysis of Y-chromosome genetic diversity published by Shi et al.  in BMC Biology has now clarified migration routes and times of settlement for East Asia, with wide-ranging implications.
Previously, it seemed equally possible that the modern humans who settled East Asia came either from Southeast Asia or, alternatively, migrated southward from northern Asia. Researchers have long noted a significant genetic difference between northern and southern East Asian populations that could be interpreted to support either scenario – or some mix of the two. Both archaeological and genetic evidence for settlement times were also ambiguous [2,3]. Timings for southern East Asia ranged from an earliest date of 30,000 years ago to 50,000 years ago at the latest, while dates for the settlement of Siberia ranged from 40,000 to 45,000 years ago, or even earlier. However, the new data from Shi et al.  suggest that our species reached southern East Asia 60,000 years ago, twice as long ago as most previous estimates, and then spread rapidly northward.
The amount of genetic diversity in present-day populations is a useful variable for inferring geographic origins and migration routes. Africa was pinpointed as the homeland of Homo sapiens because of the higher genetic diversity among Africans compared with populations elsewhere in the world, while the last geographic regions to be settled, South America and the Pacific Islands, show the lowest genetic diversity. Greater variation has been noted among Africans not only in their genes but in variables such as craniometrics, dental traits and even skin color [4,5].
The original ‘out of Africa’ hypothesis of modern human origins and subsequent pattern of global migration was based on mitochondrial DNA (mtDNA) evidence, which revealed a series of population bottlenecks and a progressive loss of diversity moving away from East Africa. mtDNA, because it is located outside of the cell nucleus, is inherited only through the female line. In contrast, the Y chromosome is passed only from father to son, and so can be similarly used to follow the male line. Both mtDNA and most Y-chromosomal DNA are non-recombinant and analysis of their inheritance is therefore more straightforward than for other parts of the genome, which are mostly scrambled samples of DNA from both parents. Human populations on the branches of the mtDNA or Y-chromosome ‘tree’ can be distinguished by sets of accumulated mutational differences – or haplotypes – in stretches of DNA. Because these mutations accumulate at a fairly regular rate over time, they can be used as a ‘clock’ to estimate the time of human population splits.
Reconstruction of human origins and migration now mainly relies on the Y chromosome because it is much larger than the mitochondrial genome, consisting of tens of millions of nucleotides compared to the 16,000 of human mtDNA. Thousands of differences can be found in Y-chromosomal DNA from different human populations. The different Y-chromosome haplotypes function as signatures for different human lineages and are often highly associated with different geographic regions, making them extremely useful for tracing human origins and migration. […]
Continue reading: Timing the first human migration into eastern Asia