We cannot avoid recognizing these late Neandertals as the same sort of creatures as ourselves: upright, talking apes with a capacity for technological innovation and symbolic behavior. Questions about interfertility take on a lesser importance in the light of that admission.
Ever since Neanderthals were discovered more than 150 years ago (see Chapter 5), scientists have debated just about every aspect of their biology. Based on the distinctive features of Neanderthals (Chapter 4) is easy to see why King considered Neanderthals to be a different species from humans, christening them Homo neanderthalensis. Like other scientists of his time, King also inferred mental capacity from the shape of the cranium, considering Neanderthals to be low-brows in more than one sense of the word. Between 1911 and 1913, paleontologist-artist Marcelin Boule published illustrations depicting Neanderthals as stooping hairy beasts with grasping toes. This too did not help Neanderthals with their image problem. Boule's conception held sway until 1957, when Straus and Cave showed that Boule had misread the evidence, and that Neanderthals walked upright just as we do (281).
Ideas about Neanderthals began to change in the 1950s, in part because the field of physical anthropology itself was transforming. In the wake of World War II, physical anthropologists repudiated the idea that there are races or types of humans with distinct physical and mental attributes. Instead, the consensus view was, as it is today, that there are no clear physical or mental divisions among human populations along racial lines, that mental attributes are not linked to physical attributes, and that there is no evidence that human populations differ in intelligence. Racist thinking, it was argued, had led to a serious misunderstanding and Neanderthals were welcomed back into our species. Our modern understanding of species rests on evolutionary biologist Ernst Mayr's concept of reproductive isolation – species evolve independently of one another and become distinct if they do not exchange genes. As part of our species, the implication was that when and where Neanderthals and anatomically modern humans coexisted, they could have interbred to produce fertile offspring. By extension, today's humans (though in need of a time machine to do it) could have mated with Neanderthals and had children who themselves were fully capable of reproducing.