He purports to show that the percentage of Neandertal DNA depends on distance from Ethiopia. Figure 4 doesn’t however seem to show that, instead having an west-east gradient across Eurasia. However his model should show a step function, as under it each bottleneck should produce a more homozygous and slower evolving population - he should be predicting that Native Americans have more archaic DNA than Eurasians, though by a small amount as the bottleneck was relatively recent.(Possible counterargument - homozygosity increasing on the frontier of population expansion, which would smear out the steps.)
He rather glosses over the distribution of Denisovan DNA, which is rather more unevenly distributed than that of Denisovan DNA. Why are neandertal alleles found in Africa, but not Denisovan ones? Why are archaic African alleles only found in Africa?
He assumes an out-of-Africa bottleneck. But he also offers an alternative explanation (African populations evolving more rapidly) for much of the evidence for the out-of-Africa model. But he still has the mtDNA and non-pseudoautosomal region of the Y chromosome to support out-of-Africa.
His model should predict that Eurasian AMH alleles are less distant from Neandertal ones that African ones. By focusing on base pairs, rather than on longer stretches of DNA up to nearly full genomes, he has missed the opportunity to perform additional tests on his hypothesis.
How much faster does he propose African populations are evolving? Is this a plausible number?