More Hobbit press, and “reverse evolution”

There’s a nice article in the New York Times about the Hobbit, written by John Noble Wilford, who seems to cover the human evolution beat pretty well.  It’s a nice summary of what the major hypotheses are and have been over the past few years.  Particularly, they address the idea that H. floresiensis might be the last vestiges of an ancient migration out of Africa by one of the Australopitecines or maybe Homo habilis.

There’s always that possibility.  I’m certainly not ready to discount that it may be a pathological human, or even a pathological H. erectus, but I also haven’t been keeping up with the Hobbit literature as much as I probably should be.  An ancient migration out of Africa is usually dismissed as impossible because the little Australopithecines didn’t have long enough legs to make long-distance migration efficient.  I’ve always found that argument a little confusing, though.  It’s not as if the individuals themselves had to have been walking long distances.  They could have been just expanding the outskirts of their range, little by little with each generation, or even season.  And one needs only to point to the New World Monkeys to show that long-distance migrations can indeed occur with small bodied animals, so long as sufficient resources are present on a natural raft.

The article is good, but one paragraph did jump out at me and send me into nit-pick mode:

Or could the hobbits be an example of reverse evolution? That would seem even more bizarre; there are no known cases in primate evolution of a wholesale reversion to some ancestor in its lineage.

I’m not sure why this is in here.  Nobody thinks that the Hobbit is “reverse evolution,” because such a thing doesn’t exist.  While some interpretations conclude that Flo has an australopithecine-like wrist, that doesn’t mean that it’s identical to an australopithecine, or even that the wrist is identical to an australopthecine’s wrist.  What it means is that, in a statistical analysis, the capitate groups more closely with australopithecines than with modern humans.  The Hobbit’s trapezoid also groups more closely with those from chimps and gorillas than it does with humans, but again, this doesn’t mean that it was identical.

Furthermore, not only are there no cases of “wholesale reversions” in primate evolution, but I’ve never heard of such a thing happening in any lineage at all!  Sure, there are atavisms, or reversions back to a “primitive” trait, but those result in a descendent with an ancestor-like trait, not a perfect duplicate of the ancestor.  “Reverse evolution” doesn’t happen.  Once an animal evolves, it can’t un-evolve.  It can loose traits, or re-evolve a basal trait, but a human isn’t going to “reverse evolve” into an australopithecine, and a bird isn’t going to “reverse evolve” into a dinosaur.  That bird may re-evolve teeth, but that wouldn’t make it a dinosaur.  The analysis of the wrist may lead us to the conclusion that the ancestor of the Hobbits left Africa before our modern wrists had evolved.  It may even lead us to the conclusion that the Hobbits left Africa with a modern wrist and then evovled a wrist that looks more primitive, but even that’s a stretch.  What it doesn’t lead us to conclude is that the ancestor of the Hobbits left Africa and then reverse evolved back into Australopithecines.

References:

Tocheri et al. (2007) The Primitive Wrist of Homo floresiensis and its Implications for Hominin Evolution.  Science 317: 1743-1745.   DOI: 10.1126/science.1147143

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One response to “More Hobbit press, and “reverse evolution”

  1. RBH May 2, 2009 at 7:13 pm

    I’d still like to see another skull. One data point does not a new class make.

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