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New African genomes: Complicated migrations and strong selection - Ars Technica

New African genomes: Complicated migrations and strong selection - Ars Technica

Oct 28, 2020 2 mins, 7 secs

To understand our shared genetic history, it's inevitable that we have to look to Africa.

Unlike elsewhere on the planet, however, African populations were present throughout our history—they weren't subject to the same sorts of founder effects seen as populations expanded into unoccupied areas.

Sorting out all of this would be a challenge, but it's one that has been made harder by the fact that most genome data comes from people in the industrialized world, leaving the vast populations of Africa poorly sampled.

But identifying these populations can be hard when there are so many; the study mentions that there are over 2,000 ethnolinguistic groups in sub-Saharan Africa, and only a small number of those have been sampled.

But even there, it's limited, adding only 50 new ethnolinguistic groups and two vast regions of the continent represented by people from a single country (Zambia for Central Africa and Botswana for Southern Africa).

They do find, however, that looking beyond West African populations would give us the biggest increase in previously undescribed variation.

The second-largest difference mirrored the geographic distance between Niger-Congo speakers in West Africa and those in Southern Africa.

The researchers use this data to argue that the Bantu Migration passed through Zambia on its way to Southern and East Africa, but their data includes a lot of people from Zambia, so it's not clear whether that might have biased their results.

One looked genetically like East Africans but was located in West Africa.

People from the far west of Africa have a large majority of their DNA from what you could call a West African source.

But as you move east into Central Africa, there's an increasing amount of what you'd have to call West-Central African DNA, which is then joined and later displaced by Central African and then a smattering of Southern and East African sources.

There's a sudden shift to a majority from East African sources as you exit Central Africa moving east, with an increasing contribution from Southern Africa if you turn south a bit.

And, these being African populations, there's evidence of selection for that in some of them.

But hemoglobin isn't the only route to malaria resistance, and some populations show evidence of selection for a different gene (G6PD).

At this stage, we can examine a piece of DNA and determine that it probably originated in, say, a West African population.

There's evidence that, much as Eurasian populations picked up archaic DNA from Neanderthals, African populations picked up DNA from earlier branches from the human family tree.

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