Modern humans descended from not one, but at least 2 ancestral populations that drifted apart and later reconnected, long before modern humans spread across
According to the paper, they tested ten different split-and-merge scenarios and this one was the most likely. But they give some important caveats, including:
They assume that the smaller group had a more-or-less constant population size—if it fluctuated significantly, some of their other predictions on the dating of the split and merge might be off.
They can’t rule out more complicated scenarios, like three or more splits and merges (but they can rule out the simpler scenario of no splits).
They do say that they tested their model on a number of other species (including chimps, bats, and dolphins), and got results consistent with those species’ known evolutionary histories.
According to the paper, they tested ten different split-and-merge scenarios and this one was the most likely. But they give some important caveats, including:
They assume that the smaller group had a more-or-less constant population size—if it fluctuated significantly, some of their other predictions on the dating of the split and merge might be off.
They can’t rule out more complicated scenarios, like three or more splits and merges (but they can rule out the simpler scenario of no splits).
They do say that they tested their model on a number of other species (including chimps, bats, and dolphins), and got results consistent with those species’ known evolutionary histories.