Modern life had a single origin

If you’ve been reading the evolution websites, you’ll know about the in this week’s Nature by Douglas Theobald. (You may remember Theobald as the author of one of the greatest creationism-refuting websites of all:If you haven’t seen it, you should.) In the new paper, Theobald makes a few conservative assumptions to show that the probability that all living species descend from a universal common ancestor is infinitely higher than any other hypothesis, including those of multiple origins of the kingdoms (Bacteria, Eukarya, and Archaea) or of rampant horizontal gene transfer betweeen species that would, by mixing genomes, make life look as though it had a single origin when it didn’t.

Fortunately, I delayed posting on this long enough so that others did the job for me: these include It’s pretty airtight evidence for evolution, since the hypothesis that trumped all others is that of a single origin of life, with the proteins of existing species showing a pattern of similarity and divergence reflecting the branching bush of evolution.

I’m not sure how creationists will respond to this, but I suppose they could maintain that the data show only that God created life in this way because he needed to give similar proteins to similar species. That, of course, would require one to believe that those similarities just happen to mimic the similarities expected under evolution. Proteins group not by lifestyle, but by ancestry. Bats have proteins that resemble those of rats more than those of birds, and whales have mammal-like rather than fish-like proteins. A marsupial mole has virtually the same niche, and looks almost the same as, a placental mole, but its proteins are more similar to those of a kangaroo.