My post The paradigm is dead, long live the paradigm! expressed to some extent my befuddlement at the current state of human evolutionary genetics and paleoanthropology. After the review of the paper of possible elevated admixture with Neandertals on the dystrophin locus a friend emailed, “Remember when we thought everything would be so simple once we could finally see this stuff?” Indeed I do remember. The fact that things aren’t simple is very exhilarating, but it is also a major quash on theoretical clarity. Science is after all not a collection of facts, but it is in part facts which one can sieve through a analytic framework.
In hindsight with the relative robustness of ancient DNA results we can make some assessments about the role of human bias within particular heuristic frameworks over the past generation. From the mid-1980s up until 2000 it was victory after victory for the Out-of-Africa with total replacement model. The rise of mtDNA and Y chromosomal lineage studies seemed to buttress the idea of common descent from neo-Africans within the last 100-200,000 years for all human populations. There wasn’t much of a perturbation from this march toward paradigm ascendancy in the aughts, except that there were now also now a trickle of papers which claimed to phylogenetic “long branches” in the human genome. The 2006 Evans et al. paper, Evidence that the adaptive allele of the brain size gene microcephalin introgressed into Homo sapiens from an archaic Homo lineage, was probably the one that made the biggest media splash. But these were inferences. Subsequent analysis of the draft Neandertal genome seems to suggest that in fact the microcephalin allele in question did not introgress.
Case closed? Obviously not. Now we’re in a different era. The Evans et al. paper may have wrong in the specifics, but its general framework seems to likely have been validated: there are genetic lineages in the modern human genome which are not derived from the neo-Africans. But, let us remember that the overwhelming majority of the human genome is neo-African. A reasonable interval for non-Africans is 90-99% neo-African. But, a non-trivial minority has introgressed or admixed from other lineages. Out-of-Africa is mostly correct, but in some ways so is Multiregionalism. But how do we describe this? “Weighted multiregionalism”? “Mostly Out-of-Africa?” The old terms were nice because they were punchy and precise. If you look at Multiregionalism or Out-of-Africa in Wikipedia the newest results are noted, but it doesn’t seem that they’ve been integrated into the analytic narrative. Yet.