Genetic studies of individuals from geographically diverse human populations help to clarify the dispersal of modern humans from Africa to every corner of the Earth.
From our evolutionary birthplace in Africa, modern humans have migrated to nearly every habitable corner of Earth, from the inhospitable frozen wastelands of Siberia to the muggy African plains.
The number, timing and routes of human dispersals out of Africa have implications for understanding our past and how the past influenced contemporary patterns of human genomic variation.
Three studies online in Nature (Malaspinas et al., Mallick et al. and Pgani et al.) have described 787 new, high-quality genomes of individuals from more tan 270 populations across the globe, providing apportunities to refine and extend current models of historical human migration. Mallick et al. and Pgani et al. made great efforts in cataloguing genetic data from under-studied indigenous populations, which are often difficult to access and are rapidly disappearing. These include African populations, which have considerable genetic, linguistic and cultural diversity. Similarly, Malaspinas et al. describe the first extensive survey of human genetic diversity in the poorly studied Australia.
Three studies online in Nature (Malaspinas et al., Mallick et al. and Pgani et al.) have described 787 new, high-quality genomes of individuals from more tan 270 populations across the globe, providing apportunities to refine and extend current models of historical human migration. Mallick et al. and Pgani et al. made great efforts in cataloguing genetic data from under-studied indigenous populations, which are often difficult to access and are rapidly disappearing. These include African populations, which have considerable genetic, linguistic and cultural diversity. Similarly, Malaspinas et al. describe the first extensive survey of human genetic diversity in the poorly studied Australia.
The new high-quality human genetic diversity information afforded by these studies allows new inferences to be made about our migration out of Africa. There are currently two conflicting models for such human dispersal. The first hypothesizes a single migration that occurred around 40,000-80,000 years ago, which means that all present-day non-Africans trace their ancestry to a single population. On the contrary, the multiple-dispersal model states that an initial migration occurred 120,000-130,000 years ago, settling the southeast of Asia and Australasia. This early dispersal was followed by a second migration from Africa, which resulted in the peopling of Eurasia.
Pagani et al. found that about 2% of genomes from individuals of Papua New Guinea ancestry indicate that their ancestors separated from Africans earlier tan did other Eurasians, being consistent with a multiple-dispersal model. Cranial morphology and other genetic data also support the idea of an early expansión.
Figure 1. Cave painting in Laas Geel (northwestern Somalia). Three genetic studies of individuals from geographically diverse populations provide clues about human history, incluiding when and how many times humans moved out of Africa and throughout the world.
Malaspinas et al. and Mallick et al. consider a different sequence of events, in which all contemporary non-Africans branched off from a single ancestral population. Malaspinas and colleagues provide evidence that, on leaving Africa, modern humans immediately separated, leading to two waves of dispersal. One wave led to the peopling of Australasia, whereas the other contributed to the peopling of Eurasia. Mallick and co-workers propose that this early separation instead occurred between west and east Eurasians, meaning that present-day people in Australia and Papua New Guinea might be descended from the same wave as east Asians. However, neither Mallick et al. nor Malaspinas et al. exclude the possibility of multiple out-of-Africa dispersals. Indeed, their models are consistent with earlier dispersals, as long as these early voyagers made little or no contribution to the gene pool of contemporary non-African population (which is essentially what Pagani et al. find).
These studies fill in some missing pieces in the puzzle of human history, but many fascinating questions remain. The continued sampling of human genomic diversity promise to reveal more secrets about our past. In my opinion, it is vital to know the path (or paths) that early human took to expand through Earth, in order to be able to answer great questions related to anthropology and genetics. Even so, it is still necessary further investigation to clarify the migration of modern humans from Africa. We have to take into account that these events occurred thousands of years ago, which complicates the investigation enormously. In these past few years much progress has been done in this field, thanks to the new technology in the analysis of human genomic diversity, but I believe newer technology will be needed that could shed somo light on this matter. What is certain and what all of us agree is that the discovery of this fact will be a milestone in modern science.
References
1.- Malaspinas, A.-S. et al. Nature http://dx.doi.org/10.1038/nature18299 (2016).
2.- Mallick, S. et al. Nature http://dx.doi.org/10.1038/nature18964 (2016).
3.- Pagani, L. et al. Nature http://dx.doi.org/10.1038/nature19792 (2016).
4.- Baudelaire, C. Journaux intimes (Crès, 1920).
5.- Stringer, C. B. & Andrews, P. Science 239, 1263-1268 (1988).
No comments:
Post a Comment