Thursday, April 10, 2008

Loss of Legs, or Acquisition of Traits?


French researchers uncovered a 92-million year old fossil of a snake with two "unmistakeable leg bones".  The interesting thing here is not that we have a beautiful example of a transition fossil (or a fossil of a descendant of a transition species), we have plenty of those, but it's entertaining to watch creationists once again move the goal-posts for the burden of proof on evolution.

Over at AiG they have scrambled to explain away such a nice bit of evolutionary history.  Here's a funny quote:

"Bible believers should be wary of rushing in with comments about the serpent in Genesis. This fossil was probably formed in Noah’s Flood, hence the creature it represents was in existence some 1600 years after the cursing of the serpent to crawl on its belly."

Not quite sure where the evidence for this lies, or even what it is supposed to mean.  So basically, serpents where cursed to crawl on their bellies, but then another snake with small hind legs was designed?  (Incidentally, why did god curse some lizards and not others?  And while I'm at it, why curse any of them just because the devil dressed up like a one?  Seems sort of reactionary if you ask me).  He was, however, kind enough to leave rudimentary legs on the cursed serpents.  Is this because he felt bad for them having to copulate without legs?  I'm sure we can all imagine how difficult that would be, and it was kind of him to make this beneficent gesture.  Maybe he felt bad for overreacting.

They also go to the oft utilized but always silly - scientists debate the details, therefore they are wrong - argument:

"The findings are controversial. Some evolutionists claim that snakes came out of the sea, from something like a mosasaur. Others insist on a land-based origin. The controversy still rages. In other words, the fossils are open to interpretation."

This is factually incorrect, but more importantly, it's stupid.  Scientists debate the details, but either way, they agree that the snakes evolve.  You can't have your cake and eat it too.  If you believe that scientists are completely wrong about evolution, you can't use their arguments to support your own.  They're wrong, remember?

There was, at one point, a debate as to whether snakes lost their legs on land or in water. There was fossil evidence that suggested it may have happened in the ocean.  In the end researchers used molecular techniques to create a family tree of snakes and lizards, and found that the only ocean-dwelling lizards known (they're now extinct, but are closely related to monitors) are too far up the evolutionary tree to be the descendants of snakes, suggesting that legs were lost on land and then some snakes moved back into water.  It's still possible that another fossil will come along and change that, but this is what the evidence says for now.

Another contradictory point made by AiG:

"Even assuming it could be established that the ancestor of snakes today had legs, creationists have no problem in principle with loss of features through natural processes. Development of leglessness is not evidence for molecules-to-man evolution, which requires addition of newgenetic information. Loss of legs could be achieved through degeneration of the DNA information sequences that specify leg development."

How is this any different from evolution?  Loss of a feature is gain of a trait.  In fact, they've explained this one aspect of evolution fairly nicely in the last sentence.  However, for this to explain the loss of legs, you have to believe in natural selection.  You believe that degeneration of DNA leads to new traits, and that these traits can then be selected for if they are advantageous.  If you don't believe that it's advantageous, then how could degenerate DNA persist in snakes?  So, if you agree that natural selection can occur from loss of information, why are things like gene duplication so hard to accept?  They have been observed and documented!  It really boils down to an argument from incredulity, or one from ignorance, take your pick.  You can't imagine, or don't understand how such a thing could happen, therefore it didn't.  Not exactly convincing logic there.

I know, I know.  I'm arguing against people who have already made up their minds.  But the fallacies here are unforgivable.

DS

1 comment:

snail.sfury said...

So, that were some interesting bits of knowledge about legged snakes.

As for the creationist stance... as a European, with fewer creationists around, I find it somewhat alien, quite silly, and pretty disturbing.

This page is a bit newer and gives a more extensive creationist argument than the one you mention (but using some of the same text).

I don't really know how representative it is of creationists in general...

The "Possible biblically consistent explanation" is too childish for me to go into here (even if there's some real science woven, rather undeservedly perhaps, into the crap). Let's see for the "Proof of evolution?" bit.

When evolutionists say "snakes with small legs evolved from something else", they are making no claim (at that point) whether this was by addition or alteration or removal or suppression of genetic information. This kind of snake fossil is indeed not necessarily 'proof of evolution-in-the-sense-of-acquiring-novel-traits'; but evolutionists never claimed that that was the only kind of evolution possible. So the creationists (on those pages) shoot at the wrong target.

They also get muddled with homology and analogy (homoplasy). They say that IF (could be in principle) the snake legs are an example of homoplasy, that goes counter evolutionism, as

" [...] homology is alleged to be the evidence for evolution (despite many problems—see Common structures = common ancestry?) Appeal to homoplasy is really explaining away evidence that doesn’t fit the paradigm, and indeed such explaining away is ubiquitous. "

But of course homoplasy is perfectly reasonable within an evolutionist framework. Maybe it doesn't point so much at the descent-with-modification aspect of darwinism as homologies do, but it points more at the adaptation-to-similar-niches aspect, which is an integral part of 'the paradigm'.

[They also seem to conflate the 'turning off' of genetic code during ontogeny and the turning off (or elimination) of genetic code on an evolutionary scale. In the 'biblically consistent' bit.]

So yeah, just more to add to your list of fallacies.

In the end, fencing with fossils is a bit of a wearisome game, as there will always be gaps in the fossil record, making it hard to prove some things conclusively. This is especially so for traits that disappeared, reappeared, lasted longer in certain lines than in others, etc. I suppose one can always concoct some mixture of fossil evidence or fossil gaps, good (or less good) scientific ideas, and baseless religious stories. In the end, to grasp evolution you also need a certain logic and factual open-mindedness, and a willingness to question everything down to what the vicar or the pope says, which just doesn't rhyme with "revelation"-based belief.