"What remains unclear is the outcome of the interbreeding experiment posed in science-fiction novels. Did some invading Cro-Magnon men mate with some Neanderthal women? No skeletons that could reasonably be considered Neanderthal-Cro-Magnon hybrids are known. If Neanderthal behavior was as relatively rudimentary, and Neanderthal anatomy as distinctive as I suspect, few Cro-Magnons may have wanted to mate with Neanderthals. Similarly, although humans and chimps continue to coexist today, I'm not aware of any matings. While Cro-Magnons and Neanderthals weren't nearly as different, the differences may still have been a mutual turnoff. And if Neanderthal women were geared for a twelve-month pregnancy, a hybrid fetus might not have survived. My inclination is to take the negative evidence at face value, to accept that hybridization occurred rarely if ever, and to doubt that living people of European descent carry any Neanderthal genes." (Chap. 2, p. 53)

"Breakdown of murders caused by sexual...