Monday, January 31, 2011

Human species?

Previously, I commented on the status of Neandertals as a separate species or just a subspecies of modern humans, Homo sapiens (here and here). Some of my fellow young-age creationists have insisted that anything descended from Adam and Eve must necessarily be Homo sapiens, so they want to make Neandertals just a subspecies of modern humans. If you really evaluate the issue, it's just biologically naive and biblically unnecessary to demand that human be equivalent to the species Homo sapiens. Oddly enough, Reasons to Believe seems to agree with young-age creationists on the species status of humans. They insist that only Homo sapiens are descendants of Adam and Eve, but they want you to think of Neandertals as non-human, so they try to exclude Neandertals from the human species. They're even willing to misrepresent published claims to do so.

For those keeping score, here's how it all stacks up:
1. I think Neandertals (and certainly Denisovans) are separate species from Homo sapiens, and we're all descended from Adam and Eve.
2. Many creationists think it's necessary to view Neandertals (and probably Denisovans also) as the same species as modern humans in order for them to be considered descendants of Adam and Eve.
3. RTB thinks that Neandertals (and probably Denisovans) are separate species from Homo sapiens and therefore not descended from Adam and Eve.

Confused yet? Sure you are... I know I am. I think positions #2 and #3 are operating on a view of species as something really special, something that could only originate by God's special creation. Biologically, that's just unrealistic. Species designations slip and slide all over the place, and this was something that Darwin emphasized in Origin. Furthermore, Darwin's biogeographic arguments alone should be sufficient to settle any question about species arising from other species.

I say all that as preface to a new piece by Ann Gibbons published last week in Science. She asked a number of individuals to share their perspective on the species status of Neandertals and Denisovans. The results were as I expected, and I thought they might be illuminating to some lingering misunderstandings of the specialness of species. For those who don't have a Science subscription, here's a few interesting snippets:
The draft versions of the Neandertal and Denisovan nuclear genomes show low levels of interbreeding between each of them and modern humans. Apply Mayr's definition strictly, and all three must be considered Homo sapiens. ... But that's a minority view among paleoanthropologists. Many consider Neandertals a species separate from modern humans because the anatomical and developmental differences are "an order of magnitude higher than anything we can observe between extant human populations," says Jean-Jacques Hublin, a co-author of [Neandertal genome researcher Svante] Pääbo's at Max Planck.
I briefly noted before that Pääbo was careful not to express any opinion on the species status of Neandertals, but here he makes that intentional ambiguity crystal clear:
"I think discussion of what is a species and what is a subspecies is a sterile academic endeavor," says Pääbo ... "Why take a stand on it when it will only lead to discussions and no one will have the final word?"
That's an extremely helpful perspective that we can all learn from.

P.S. Remember how Hugh Ross and Fuz Rana both claimed that Pääbo's research team "discovered" that the Neandertal genome was too different from the modern human genome for them to be the same species? (If not, click here to refresh your memory.) It was demonstrably false when they first said it, and now even more so. Will they issue a correction? Will they remove the offending podcast?

Gibbons. 2011. The species problem. Science 361:394.

Feedback? Email me at toddcharleswood [at] gmail [dot] com.