Title

Did ancient humans really mate with almost anything they encountered on two legs, or is this a flawed story that is simply too big and too romantic to be questioned?

Abstract

It is now regarded as incontrovertible truth that non-African humans carry a few percent Neanderthal DNA as a result of historical inter-breeding.  This is despite many aspects of biology that make this unlikely, including the probable low fertility, low viability and low attractiveness of hybrid offspring, the extent of overlap in time and space between the populations and the lack of introgressed sex chromosomes or mitochondrial DNA. 

What is fact is that non-Africans are more related to Neanderthals than Africans.  However, there are two possible explanations: either non-Africans are brought closer because they carry introgressed fragments, or Africans have diverged more through a higher mutation rate.  To date, all papers that I have read in the mountain of literature reporting introgression assume that mutation rate is constant, leaving only one possible inference, inter-breeding.

I have spent the last 6 years or more devising ways specifically to distinguish between inter-breeding from mutation slowdown.  In every single case, a fair test favours mutation slowdown rather than inter-breeding, often to the point where any inherited legacy is indistinguishable from zero.  Here, I present a selection of my most recent results which I discuss in light of how and why the accepted story became so firmly established.