The ancient DNA evidence has completely revised this picture.

The interactions between ancient human groups were not rare, marginal encounters.

They were sufficiently frequent and sufficiently fertile to leave lasting genetic contributions in modern populations.

Modern humans of non-African ancestry carry Neanderthal DNA that can be shown to influence their immune system, their skin, their susceptibility to disease.

Populations of Oceania carry Denisovan DNA at levels that imply substantial ancient interbreeding.

And now, with Denny, we have direct evidence of a first-generation hybrid — an individual born to parents from two different ancient human lineages who was not a rare aberration but a product of a world where such encounters could happen and did happen.