The roots of modern man lie in eastern Africa, so the scientific consensus maintains, supported by ample evidence. And, before we left our cradle to spread throughout the world, a lot of interesting things happened there. Two recent studies present clues about some intriguing and complex first steps of Homo sapiens.
The first one, published in PLOS ONE, looks at fatty acids and early human expansion throughout Africa.
Docosahexaenoic acid (DHA), an important LC-PUFA.
(Source: Wikimedia Commons, author: Timlev37)
Brain food?
(Source: Wikimedia Commons, author: Blu3d)
Our brains are quite fat, and, as such fatty acids are important for its proper functioning. More specifically, long chain polyunsaturated fatty acids (or LC-PUFAs) are crucial for the development, structure and functioning of the brain. These LC-PUFAsare relatively rare in our food, and one of the main sources is fish-oil. No wonder then, that our early big-brained ancestors seemed to be bound to the great lakes in eastern Africa. But, after many tens of thousands of years, they started spreading throughout the continent at around 60-80 kya, apparently released from their LC-PUFA imposed shackles. What happened?
The researchers looked at the FADS (fatty acid desaturase) gene cluster, variations of which have been associated with an increased conversion of plant-based medium chain polyunsaturated fatty acids (or MC-PUFAs) to the important LC-PUFAs. Through analyzing the genomes of 1092 individuals, they managed to find that high-efficiency FADS variations spread throughout African populations at about 85 kya. Aha, a clue to understand the within-Africa spreading of our ancestors, the authors suggest.
But, even before all this traveling far and wide, there was plenty of interesting genetic divergence going on, so the second study, published in Science, shows.
The researchers investigated over 2 million SNPs in 220 Southern African individuals. (SNPs or single nucleotide polymorphisms are differences in the genome at a single ‘letter’, A, T, G, or C.) In doing so, they found that the Khoe-San, an ethnic group in southern Africa (actually a unification of two groups, the Khoi and the San), diverged from other African populations over 100 000 years ago, marking the earliest known divergence of all living people.
A San tribesman (Namibia).
(Source: Wikimedia Commons, author: Ian Beatty)
Furthermore, the authors found that the Khoe-San diverged themselves about 35 000 years ago, dividing into a South African group and one that settled in what is currently northern Namibia and Angola. By comparing these groups, evidence of local adaptation was found in traits such as muscle function, immune response, and UV-light protection. And, from before the early human diversification event 100 kya, there was evidence of selection concerning skeletal and neurological development.
All this early genetic variation suggests an early human history full of “admixture and stratification”. Our early Homo sapiens history turns out to be a complicated affair. Luckily, current African, and global, genomic diversity contains interesting clues.
Elementary, those dear genes.
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Mathias, R.A., Fu, W., Akey, J.M., Ainsworth, H.C., Togerson, T.G., Ruczinski, I., Sergeant, S., Barnes, K.C., & Chilton, F.H. (2012). Adaptive Evolution of the FADS Gene Cluster within Africa. PLOS ONE, 7 (9) DOI: 10.1371/journal.pone.0044926
Schlebusch, C.M., Skoglund, P., Sjödin, P., Gattepaille, L.M., Hernandez, D., Jay, F., Li, S., De Jongh, M., Singleton, A., Blum, M.G.B., Soodyall, H., & Jakobsson, M. (2012). Genomic Variation in Seven Khoe-San Groups Reveals Adaptation and Complex African History. Science DOI: 10.1126/science.1227721
