Gorillas, crabs and hominids

New research indicates that "crabs", or pubic lice, began to evolutionarily diverge after human-leading lineages and gorilla-leading lineages split. As there are very few ways to spread public lice, it suggests that there was some hominid-on-gorilloid action after speciation.

Eww, you might think. But this is to be expected in evolutionary terms. If it wasn't a case involving us or our near relatives, we'd say, "sigh... yet another case of divergent species occasionally doing the nasty". For instance, ducks, which have a deep evolutionary history, will often hybridise. Even if the two species didn't actually hybridise, as they are supposed to have done with chimp-leading lineage species, there may have been attempts at sex, and why would we expect otherwise?

Cross-species sex is a widespread phenomenon in vertebrate biology. We have been misled by our "intuitions", based on the one hand on an over-strict application of reproductive isolation concepts of sex, and on the other of projection of moral standards.

Alan Templeton's classic paper on species concepts has a section entitled "Too much sex". It's worth reading just for that.

Templeton, Alan R. 1989. The meaning of species and speciation: A genetic perspective. In Speciation and its consequences, edited by D. Otte and J. Endler. Sunderland, MA: Sinauer.

Late note: John Hawks notes that a better explanation is that gorillas were eaten by hominids, as they are today, which would allow transfer easily. But I still like the horizontal hominoid hypothesis.