Evolution Evolution

4 comments August 8th, 2007at 10:57pm Posted by Eli

So, apparently, our family tree has gotten a bit forked up:

The discovery by Meave Leakey, a member of a famous family of paleontologists, shows that two species of early human ancestors lived at the same time in Kenya. That pokes holes in the chief theory of man’s early evolution — that one of those species evolved from the other.

And it further discredits that iconic illustration of human evolution that begins with a knuckle-dragging ape and ends with a briefcase-carrying man.

The old theory is that the first and oldest species in our family tree, Homo habilis, evolved into Homo erectus, which then became human, Homo sapiens. But Leakey’s find suggests those two earlier species lived side-by-side about 1.5 million years ago in parts of Kenya for at least half a million years. She and her research colleagues report the discovery in a paper published in Thursday’s journal Nature.

The paper is based on fossilized bones found in 2000. The complete skull of Homo erectus was found within walking distance of an upper jaw of Homo habilis, and both dated from the same general time period. That makes it unlikely that Homo erectus evolved from Homo habilis, researchers said.

It’s the equivalent of finding that your grandmother and great-grandmother were sisters rather than mother-daughter, said study co-author Fred Spoor, a professor of evolutionary anatomy at the University College in London.

But considerably less icky.

There remains some still-undiscovered common ancestor that probably lived 2 million to 3 million years ago, a time that has not left much fossil record, Spoor said.

Overall what it paints for human evolution is a ”chaotic kind of looking evolutionary tree rather than this heroic march that you see with the cartoons of an early ancestor evolving into some intermediate and eventually unto us,” Spoor said in a phone interview from a field office of the Koobi Fora Research Project in northern Kenya.

(…)

”The more we know, the more complex the story gets,” [Bill Kimbel, science director of ASU’s Institute of Human Origins] said. Scientists used to think Homo sapiens evolved from Neanderthals, he said. But now we know that both species lived during the same time period and that we did not come from Neanderthals.

Now a similar discovery applies further back in time.

I don’t think this is really all that shocking. Why should we assume that the evolution of homo sapiens was an almost completely straight line, with hardly any extraneous branches? Lots of animals come in all sorts of different varieties, with cousins sprouting off at all kinds of branching points, so why should we be different? Evolution does not have a plan; genetic mutation just throws a whole bunch of stuff at the wall, and natural selection determines what sticks.

Yes, the fact that creating humans was not evolution’s sole purpose does put a dent in our sense of specialness, but it’s the truth. All we are is just another animal, whose brain just happened to reach critical mass. And sometimes I’m not even sure about that.

(Note: Stephen Jay Gould was a big proponent of the “bushy” theory of evolution, in which lots of varieties of creatures evolve, with most of them dying out. I highly recommend his book on the subject, Wonderful Life, which focuses primarily on the incredibly bizarre creatures of the Pre-Cambrian Burgess Shale.)

Entry Filed under: Science

4 Comments

  • 1. shoephone  |  August 9th, 2007 at 3:14 am

    So then is there a new working hypothesis of why and how Neanderthals died out?

  • 2. Eli  |  August 9th, 2007 at 10:08 am

    Not that I know of – I think the current theory is that we outcompeted and maybe even actively exterminated them (I may be reaching on the second part, but it would probably be in character), and I can’t see where that would need to change.

    Parenthetically, there’s a book called Hunting The Ghost Dancer, by A.A. Attanasio (very good, very mystical writer, and I normally don’t like mystical), set in a time where the neanderthals (known as ghost dancers) are almost extinct, but are revered and feared for their rapport with the supernatural. Not Attanasio’s best work, but still pretty good stuff.

  • 3. shoephone  |  August 10th, 2007 at 4:24 am

    I heard one of the scientists on NPR yesterday talking about this “discovery”. She said the skull size of one of the specimans found was small enough to fit into the palm of her hand, and that carbon dating revealed that the person was full grown, about 18 years of age. Very fascinating.

  • 4. Eli  |  August 10th, 2007 at 9:18 am

    You would love the evolution/human origins exhibit at the Museum Of Natural History in NYC. The centerpiece is this little 3-foot-tall hominid couple walking hand-in-hand. There’s also a whole lot of stuff on some early human ancestor or cousin from maybe the million-year range, who I had never heard of and whose name I can’t recall.

    Yes, I’m very helpful…


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