I've always remembered that -- the word "species" is an artificial construct, and is the hardest concept in biology to come up with a consistent definition for. No matter how you define it, you come up with exceptions and qualifications (something I dealt with a while back in my post "Grass, gulls, mosquitoes, and mice"), and it's only our determination that nature should be pigeonholeable (to coin a word) that keeps it in the textbooks.
We had a lovely example of that announced this week, when we learned that a stunningly well-preserved 3.8-million-year-old skull from Ethiopia had been identified as Australopithecus anamensis. This species had been thought ancestral to A. afarensis (the species to which the famous Lucy belonged), but the Ethiopian skull (nicknamed MRD after Miro Dora, the site where it was discovered) is the same age as the earliest clearly A. afarensis remains.
So it looks like the two coexisted at least for a while, which is actually a much more common thing than the textbook one-species-slowly-morphing-into-another model. Take, for example, our own (much more recent) ancestry, when only fifty thousand years ago there was enough interbreeding between Neanderthals, Denisovans, and anatomically-modern humans that we still find significant traces of each of those lineages in our own DNA. (When I had my own DNA sequenced, I was proud to find out that I had 284 clearly Neanderthal markers, putting me in the 60th percentile and possibly explaining why I eat my t-bone steaks rare and like running around with little to no clothing on.)
The current discovery, though, is awfully cool. Here's the skull itself, and a reconstruction of what its owner might have looked like, by the amazing John Gurche:
[Images courtesy of Jennifer Taylor, Dale Mori, and Liz Russell (right); and John Gurche and Matt Crow (left)]
As an aside, John Gurche lives in the same little upstate New York village that I do, and I was privileged to teach all three of his kids. His son, Loren, is now a paleontologist in his own right, and even when he was an eleventh grader in my AP Biology class he so clearly knew more about extinct animals than I did that I gladly asked him to contribute every time the topic came up in class.
Anyhow, the whole thing is wicked cool. Picture it; an African savanna with not just one, but several different kinds of proto-hominins running around, some of them quite human-like and others more similar to our ape ancestors. I'm always a little astonished at people who find the idea of our non-human ancestry demeaning -- I think it's grand that we're connected, in a series of unbroken links extending back three billion years, to every other life form on Earth.
And the whole thing took place, for the most part, in a smooth set of small changes, almost indistinguishable without the advantage of a huge time scale. As Charles Darwin put it in The Descent of Man, "In a series of forms graduating insensibly from some apelike creature to man as he now exists, it would be impossible to fix on any definite point where the term 'man' ought to be used."
This week's Skeptophilia book recommendation is about a subject near and dear to my heart; the possibility of intelligent extraterrestrial life. In The Three-Body Problem, Chinese science fiction writer Cixin Liu takes an interesting angle on this question; if intelligent life were discovered in the universe -- maybe if it even gave us a visit -- how would humans react?
Liu examines the impact of finding we're not alone in the cosmos from political, social, and religious perspectives, and doesn't engage in any pollyanna-ish assumptions that we'll all be hunky-dory and ascend to the next plane of existence. What he does think might happen, though, makes for fascinating reading, and leaves you pondering our place in the universe for days after you turn over the last page.
[Note: if you purchase this book from the image/link below, part of the proceeds goes to support Skeptophilia!]