I read a bit more. There definitely was introgression of West Eurasian populations into East Africa and Sudan than percolated into West Africans to the tune of about 15 million base-pairs of sequence tagged as Neanderthal. Not sure we have values for how much Yoruban ancestry is now embedded in Mbuti genomes, but it is small. So the flow of Neanderthal genomes into Central African hunter-gathers will sub-decimal dust.

But having said all that, maybe the key point Zimmer is making IS a good generalization.