What part of "increase" don't you understand?
The genome named as being “Sub Saharan”— does not assure it being “black” neccessarily or exclusively. I understand the poor use of the word’— “increase” in this broad brush application well— it’s another example of the “scholarship” of “journals” like Nature. Having a background in biochemistry/genetics has that effect on how I see this publication, to cause one to asks— “why is this being pushed with such poor science”? There is an answer.
Check out the Y-DNA haplotype of the “sub saharan” genome. There were many other genetic contributions, post Roman era. Should add, using genetic material from the mummies (cause that is all there is, and subject to the ability to date these samples) selects out the wealthy- the ruling class - not the general population of the masses— who came from everywhere.
Just for example— prior to Roman era was of course the Greeks, Macedonians, etc. Post Roman?-— The Tuaregs derive from from the Crusaders— European Crusaders, is just one example. You point out another prominent “displacement” by the Semitic Assyrians (that had to include genes from Alexander’s reign).
https://en.wikipedia.org/wiki/Y-DNA_haplogroups_in_populations_of_Sub-Saharan_Africa
Point was making is that this kind of “scholarship” is both faulty in logic and method, and.. politically driven— by even current African politics (see: obamaumao is helping form the NBA for africa—the kenyan in chief/muslim slaver family).