We just watched the BBC 2 part documentary "Neanderthals - Meet Your Ancestors "

Current theories are that 'modern' humans migrated out of Africa and interbred with their distant cousins
to produce Europeans.

Present day Europeans carry part Neanderthal DNA.

Modern humans who stayed in Africa don't.

Part 2 of the documentary suggested [too briefly] how this might affect health conditions differently
for Europeans and Africans...

Not a bad 2 hours of TV...