Update: It maybe that "idiot commenter" speaks English as a second language , and so was not expressing his skepticism with sufficient nuance for my taste. That being said, this post stands as a warning to those who would waste my time. -God Bless, Razib This commenter starts out by admitting that he didn't follow all my reasoning in my post on Neandertal admixture, but proceeds to take a patronizing tone. What bullshit. I know that some of my posts make recourse to terms which are a bit technical, in fact, terms which I myself didn't grasp well until a few years ago, and whose conceptual implications and structure were somewhat fuzzy until only recently. But, it really isn't rocket science, and the basic analytic framework isn't much beyond 8th grade algebra, at least in its most general and broadest scope. Homework for those who have problems "following the reasoning": 1) Coalescent theory. 2 Selection coefficient. 3) Introgression. 4) Neutral theory. To respond to a few specific issues that idiot commenter brings up: a) Introgression of alleles (ergo, traits) maybe non-trivial despite trivial ancestry across the genome. b) Species concept debates make me highly skeptical of claims for crisp cladogenesis at a specific time and place. c) I suspect that there are multiple fitness optimums for a given environment, so the same adaptive strategy may not be found across all cognate environments for a given species. On the specific issue of why if there was admixture between Neandertals and moderns moderns do not exhibit Neandertal robust physiognomy, there are many reasons one could posit. Consider a plausible reason: modern human clothing was better at insulation than Neandertal clothing, so an extreme body morphology which maximized volume in relation to surface area was not needed (and this body form might be deleterious for whatever reason, since the Inuit approach Neandertal proportions one might look to them to see what those negative consequences might be for stocky robusticity). Nevertheless, this simply won't work for skin color, there are adaptive reasons why light skin is beneficial at high latitudes, and before a diet rich in vitamin D fortified foods emerged there was no cultural work around. Now, toward idiot commenters, why did I point to skin color and MC1R? Because the coalescence for the polymorphism extant on this locus suggests a last common ancestor around 800 K BP. Do the baby math. And finally for idiot commenters, introgression does not imply massive interbreeding or appreciable modern Neandertal ancestry! That is why there is a specifical term for it. Addendum: And no one better fucking tell me I should be nicer to commenters. In case you didn't knotice, I don't blog to maximize a comfortable readership, or foster a sense of "community." Addendum II: I should also note that there is a strong alternative candidate for why MC1R is so polymorphic: frequency dependent or diversifying selection. The various tests for selection though give conflicting results, so there is a cloud of doubt on this topic, so the possibility of introgression still stands as a non-trivial probability. It is interesting to note that in Europeans MC1R is strongly polymorphic but in East Asians it is being strong by positive selection toward fixation on one allele.