The phrase "ancestral population" refers to a group of individuals who are related to each other in the past and are the common ancestors of a present-day population. Full definition
Moeller is beginning to assemble a snapshot of the microbes in the guts of our ancient ape ancestor — in essence, a paleo gut that fit our paleo diet — and hopes to go even further back in time if, as seems likely, all mammals have evolved their unique microbiota from a common ancestral population in the distant past. (sciencedaily.com)
Thanks to this new genome, researchers have been able to determine that farmers from the Mediterranean route and the inland route are very homogeneous and clearly derive from a common ancestral population that, most likely, is that of the first farmers who entered Europe through Anatolia. (science20.com)
This doesn't change for thousands of years as these populations remain in apparent isolation in the shelter of the mountains — possibly cut off from other major ancestral populations for as long as 15,000 years — until migrations began again as the Glacial Maximum recedes, and the Yamnaya culture ultimately emerges. (sciencedaily.com)