[camle]

if there’s a ‘common ancestor’, doesnt’ that mean that somewhere along the line SOMEbody mated?

[Pharmboy]

Well, not with each other, and that is the point of this sloppy article. If there was an ancestor out of Africa who gave rise to both Neanderthals and our direct proto-human ancestors, then both Neanderthals and humans would share genes with each other AND with the common ancestor.

[allmendream]

Well of course.

Say that we have population A - this population gave rise to all human and all neanderthal populations.

Population A gave rise to population B and C and D and E and F. Populations B and C were closely related, interbred, and shared common ancestry with each other more than either does with D, E and F.

Population B leaves Africa and is the founding population that gave rise to Neanderthal.

Populations C, D, E, and F stay around Africa.

Later population C leaves Africa and is the founding population for all non-African humans. Population D, E and F stay in Africa.

Population C that gave rise to all non-African humans STARTED OUT more closely related to population B, and needed no interbreeding with population B to be more similar.

Population B dies out, leaving only populations C, D, E, and F - the founding populations of all modern human population groups.

The similarity of populations B and C could have come about because they started out more similar due to them sharing a more recent common ancestor. OR it could have come about because there was a bit of interbreeding between populations B and C. OR it could be a combination of both scenarios.