Paul Nelson isn’t happy that I explained that W. Ford Doolittle is not denying common descent when he says there was a large and diverse pool of organisms swapping genes at the base of the tree of life, and he presents a very revealing counter-argument:
Before I respond to PZ’s baseless charge, let’s see what mental image the following proposition generates:
All organisms on Earth have descended from a single common ancestor.
I’ll bet “single common ancestor” caused you to picture a discrete cell. And if you opened a college biology textbook, to the diagram depicting Darwin’s Tree of Life, you’d find that same image.
Maybe among Nelson’s clique, they imagine a single cell; I don’t know of any biologists who would, though. Do they also imagine a single pair of humans giving rising to the modern population, too?
Lineages do not have descent through single individuals or pairs in any evolutionary explanation. It’s always populations. Humans arose as descendants of a group of our ancestors who also apparently maintained a loose and slowly weakening genetic contact with the root stock and closely related primates — there was a gradual separation of the lineage over time and embodied in many individuals. The rise of life in general was even less tidily bounded in the absence of strong isolating mechanisms — the little buggers were promiscuously sloshing genes back and forth among all kinds of cells.
I’m afraid that all Nelson has accomplished with his complaint was to reveal yet again how naive and simplistic the creationist view of biology is. And we already knew that … there’s nothing new there at all.
Oh, and do take a look at Nick Matzke’s mocking of his claim about textbooks. He seems to think the bars on a cladogram represents single, discrete individuals? I think Nelson has just flunked Evolutionary Biology 101.