"If a modern human female was giving birth to a hybrid baby, part Neanderthal, could there have been obstetric problems?"

Chris Stringer author of the recent book Lone Survivors discusses cross-breeding between various branches of humanoids, " We’ve had the genomes of Neanderthals reconstructed, and yes, indeed, it shows that people outside of Africa have, on average, about 2.5 percent of an input of Neanderthal DNA in them. And, of course, it’s led to a rethinking of our relationship with them; clearly there was viable interbreeding." The various cross-species breeding is most evident with Neanderthals but recall there are a lot of players in the mix: "if we went back 100,000 years, which is very recent, geologically speaking, there might have been as many as six different kinds of humans on the earth."

Stinger gives a few more details: "Western Asia becomes a critical area for this possibility of interbreeding. It could have been 25 Neanderthals mixing with 1,000 modern humans. It doesn’t have to be a lot of Neanderthals, but clearly there might have been interbreeding somewhere like Israel or Lebanon or Syria — all possible places where we know Neanderthals lived, and at times modern humans also lived."

Why does this matter? Well, it changes how we think about what it means to be human.