The Washington Post has an article up on recent controversies regarding the relationship between Neandertals and our own lineage. Nothing too surprising, though I did note one point:
But one genetic trait of modern Europeans makes him [Chris Stringer] doubt there was any major Neanderthal input — the fact that most humans today are genetically ill-adapted to cold weather. Only some native Indian populations, as well as people in the north of Eurasia and aborigines in Australia (who experience deep cold at night), have good genetic defenses to cold. Since Neanderthals lived in Europe for hundreds of thousands of years, through ice ages and frigid conditions, they would have become genetically suited to such conditions, Stringer said. The fact that Europeans are not, he added, suggests that any Neanderthal contribution to their makeup is limited.
The logic here is that if interbreeding occurred then cold adaptations should have introgressed. I don’t know enough about human biology to speak to the veracity of Stringer’s assertions about cold adaptations, but let’s take him at face value. Let’s also assume that some interbreeding did occur. Why didn’t northern Europeans end up like Neandertals with a whole suite of cold adapted genetic responses? Well, some did, but in any case, this might be a situation where antagonistic pleiotropy was a significant constraining force. Neandertals might have developed all sorts of genetic responses to cold climates which imposed fitness costs. For Neandertals the costs might have been tolerable because there was no other option. Modern humans on the other hand might have developed alternative strategies (e.g., better clothing) which didn’t necessitate these genetic costs.
Addendum: I do want to note that we should be cautious about Stringer’s assertion, northern peoples do seem to have cold adapted metabolisms.