[amalia (OP)]

Tim contacted us with the following question:
If we share 99% of our DNA with chimpanzees then we must logically share say around 99.7% of our DNA with Neanderthals and perhaps 99.6% with Denisovans. So why do scientists say we only share 2% or 4% of our DNA with Neanderthals and Denisovans?
Do you know the answer?

[Halc]

The 2-4% figure is the likely amount of parentage Neanderthals make up in our ancestry.
So if you go back enough generations in your family tree, 2-4% of the ancestors are pure Neanderthal.  That can't be correct because there are people with zero Neanderthal ancestry still living, but even those share well over 99% of the DNA with them since the two sub-species share a common ancestry at some point (a point recent enough that the two could interbreed).  That's not saying anything, since humans and tulips share a common ancestry if you go back far enough, but that's far enough that we share far far less DNA with a tulip, and no tulip was ever my ancestor.