Thursday, February 04, 2010

 

Cool!


Scientists have been able to deduce the colors sported by a crow-sized, non-flying dinosaur, Anchiornis huxleyi. The story of how they did it is really amazing and you should go and read the article. But I was, given my own interests, interested in this:

So why would an earthbound dinosaur need feathers, particularly multi-colored ones? A likely reason, the team concludes, is to attract mates. Other possibilities are to warn away predators or rivals, to startle and flush out prey, to trap heat and keep their small bodies warm, and to prevent wear (melanin seems to toughen feather tips). ...

If the researchers can find other samples, Vinther said it should be possible to test the mate-attraction idea, since there should be color differences between males and females, as there are in modern birds.

That would help scientists counter a vexing argument from the supporters of intelligent design.

ID advocates insist that the incremental changes that feathers underwent for tens of millions of years – from the stubby, undifferentiated bristles of some dinosaurs to the highly complex feathers of modern birds – make no sense individually without the driving purpose of flight, presumably conceived by God.

"Darwin struggled with this," Hill said. "How do you get through all the intermediate steps to suddenly make [feathers] a tool for flight."

Mate selection provides the rationale for the changes, Hill said.

"Sexual selection can drive all sorts of crazy traits that aren't really that functional for getting food and surviving," he said. "If sexual selection drove the evolution of those long, elaborate plumes to be just basically palettes for color, then all of a sudden you're pre-adapted for flight. It all makes sense all of a sudden."

Ummm ... I'm not sure how strong that argument is. For one thing, if the pre-adaptation was in males only, as in the peacock's tail, how did females come to fly? If both males and females had the long plumes, that uncouples the length of the feathers from the color canvas idea. It might be more likely the other way around: long feathers might have arisen from some other adaptive advantage or from genetic drift and became colorful because of female selection.

Still it is a wonderful bit of work and another grain of sand in the vast beach of evidence accumulated in favor of evolution.
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Comments:
John, I have something I'd like to talk with you about. I've come to greatly value your perspective over the many months I've been reading your blog and commenting on it. You can reach me at carlDOTsachsATgmailDOTcom
 
I know it is not helpful - but everyone is making too simplistic assumptions here.

It is certainly possible that female Anchiornis huxleyi preferred males with colourful feathers. As a sexual marker there is no requirement for the females to have the same display, although their genes would also help the variation spread into the next generation. The sexual preference could have arisen from the females preferring males with the most effective warning display against other males, or some other reason entirely.

Similarly the preference for longer tail feathers might be also determined by sexual preference, or it might be determined by other evolutionary selection pressures - such as improved balance. It might even be 'just one of those neutral things' caused by genetic drift.

Of course it could be that longer tail feathers provide a bigger canvas for colour display and sexual selection drives the co-evolution of these traits, but the dinosaurs are still not going to fly without many other adaptations.

I've thought for a long time that the various evolutionary explanations, although having some merit (utility), are far too simple. People tend to reduce complex situations to a single teleological cause and effect. Reality is far more complicated and is the result of a network (we don't even have suitable language) of many causes and many effects.

Damn! I've pontificated now. Sorry.
 
If only males initially had these "long, elaborate plumes", the genes for their expression would have been present. And if it becomes advantageous for females to have them as well, I suspect that a very simple mutation would allow that. I seem to remember something similar being proposed for another trait in another group, but I can't remember what it was, or where I read it.
 
Nipples on men? Keep in mind developmental differentiation of basically the same starting material.

ID advocates insist that the incremental changes that feathers underwent for tens of millions of years – from the stubby, undifferentiated bristles of some dinosaurs to the highly complex feathers of modern birds – make no sense individually without the driving purpose of flight, presumably conceived by God.
This may be more of a problem if you only look and the final (or, rather, current) condition, ignoring transitional conditions.
 
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