Mailbag: The Neandertal fraction

Re: Neandertal DNA

I have a question about your "Neandertals Live!" entry written on May 8, 2010. When you say that living non-African populations (ancestry) derive 1-4% of their genomes from Neandertals, does this mean all living individuals of non-African descent have some genomic contribution from Neandertals? In other words, could one say if you or myself specifically have some kind of Neandertal DNA contribution? Or, does the 1-4% only refer to certain populations outside of Africa, while nothing can be said about individual non-Africans? For example, would having Neandertal genes be analogous to certain populations, like certain ethnicities, having a particular founder mutation on a haplotype, like sickle-cell anemia in people of African descent? In other words, some living groups of individuals have them, but not all living individuals have them?

The comparison results from the greater similarity of European (and other non-African) people to the Neandertal sequence, compared to African people. It takes 1-4% genetic contribution to explain this similarity.

That’s an unusual comparison, and it leads to unusual limitations. The number is genome-wide and we don’t know (yet) whether some parts of the genome are more consistently Neandertal than others. We also don’t know (yet) whether Africans have no Neandertal at all, or just 1-4% less than non-Africans.

We know nothing at all about individuals (at this moment) although I expect we’ll be able to say something about the heterogeneity of Neandertal contribution fairly soon.

I expect that some genes will have a very common Neandertal-derived haplotype outside of Africa because of selection, and that these will account for a predominant fraction of the admixture. But I can’t say we know this yet empirically.