Biologists have long recognized that the boundaries of one species may blur into another—by the process of hybridism, for instance. And the notion of species is especially insecure in the realm of bacteria and archaea. But the discovery that horizontal gene transfer (HGT) has occurred naturally, many times, even in the lineages of animals and plants, has brought the categorical reality of a species into greater question than ever. That’s even true for us humans—we are composite individuals, mosaics.
It’s not just that—as you may have read in magazine articles—your human body contains at least as many bacterial cells as it does human cells.
The discovery was that sizeable chunks of the genomes of all kinds of animals, including us, have been acquired by horizontal transfer from bacteria or other alien species.
DNA can be carried across boundaries, from one genome to another, by infective agents such as bacteria and viruses. Such horizontal gene transfer, like sex, has been a source of freshening innovation in otherwise discrete lineages, including ours—and it is still occurring.
This is an aspect of evolution that was unimagined by Charles Darwin. Evolution is trickier, far more intricate, than we had realized.
Read full, original post: Blurring Life’s Boundaries