There are certain dangers of speculating on the limits of science. From What it Means to be 98% Chimpanzee, by Jonathan Marks, referring to the possibility of humans inbreeding with Neandertals:
Could an extinct form of near-humans have interbred with us? Not only don’t we know, but we cannot know. Things we cannot know are outside the domain of science.
Strong word, that “cannot.” Unfortunately, Marks wrote this only 3 years before the Neandertal genome was sequenced, and 7 years before humans and Neandertals were proven to have interbred. From a summary of the findings:
- A newly mapped Neanderthal genome provides strong evidence that humans and Neanderthals interbred.
- Between 1-4 percent of the DNA of many humans living today likely came from Neanderthals.
- People of European and Asian heritage are most likely to carry the Neanderthal genes.
There is no shame in being wrong, but in Science, you should be circumspect about making absolute statements, and for Marks, this level of unreasonable certainty is troublesome. Marks frequently makes statements that lack scientific and logical rigor, and the critique of those statements is for another post.
I’d hope that someone writing a book about genetics would be able to imagine the possibility of finding similar genetic markers between two separate lineages of humanity, but Marks is only able to conceive of actual, present-day observations of productive mating as the proof that Humans and Neandertals could interbreed. But honestly, I no longer expect that sort of intelectual expression from anthropologists.