5X5 Episode 15

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5X5 Episode 15
Examining a fossilized snake - with legs.
13th April 2008

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5X5 14 5X5 16
Skeptical Rogues
S: Steven Novella
R: Rebecca Watson
J: Jay Novella
E: Evan Bernstein
Guest
M: Mike Lacelle
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Forum Topic

Examining a fossilized snake - with legs.[edit]

The BBC: Ancient Serpent Shows its Leg

You're listening to the Skeptics' Guide 5x5, five minutes with five skeptics, with Steve, Jay, Rebecca, Bob and Evan.


S: You are listening to the SGU 5x5. Mike is sitting in for Bob this week, and this week's topic is a snake with legs. Scientists have discovered a 92-million-year-old fossil snake species, which—and I'm going to butcher the Latin name right now—Eupodophis descouensi, something like that. And this snake has two small rear vestigial legs; they are clearly legs, they have all the bony parts of legs, except no toes. But they're also probably useless. They're certainly not big enough for locomotion. You guys have all seen this by now, right?

R: That doesn't mean they're useless, though.

S: That's true; I said specifically locomotion, because modern snakes like primitive boas, have really tiny little hind leg—vestigial hind legs that they use to brace themselves during copulation.

R: That's right. Doin' it. Snake sex.

S: So it could've served that purpose, but—they're larger than any living snake, but they're certainly smaller than what you would see on a lizard of the same size, for example.

J: Steve, is it possible that those legs were not being evolved away but they were being evolved back, you know, or just from nothing?

S: Well, if all you had was the snapshot of this one creature, I guess you wouldn't know, but since we know that modern snakes have no legs except for the tiny vestigial ones on some primitive snakes, and at some point in the past there were only reptiles with legs. You know, the arrow of evolution's only pointing in that one direction.

R: I'd like to point out how nice it is that the... yet another piece of evidence in favor of evolution and it happens to be in regards to sex. I just enjoy that extra little oomph there.

M: Don't those scientists know that they just created two gaps?

R: That's true; there's one on either side.

J: Yeah, there's two more gaps now.

S: Yeah.

R: And also, I looked this up on a Christian forum just to see how people were reacting. A fundamentalist Christian forum. And a lot of people are saying "Well, you know, in the Bible it said that the snake had legs originally, and God took them away as punishment for that whole apple debacle." Yeah.

J: So, what did God say? Did God go, "I want those snakes legless, Michael."

R: I think he said "I'd like those snakes legless over the next couple of millions of years."

J: Yeah, but take your time with it.

S: Yes, slowly over time. Yeah, well, one—Answers in Genesis cautions believers not to use that argument because they say, quote, "this fossil was probably formed in Noah's flood, hence the creature represents was in existence some 1600 years after the cursing of the serpent to crawl on its belly." So there you go. So there's some dissension in the ranks there.

R: That makes much more sense.

E: They also say "development of leglessness is not evidence for molecules-to-man evolution, which requires addition of new genetic information. Loss of legs could be achieved through degeneration of the DNA information sequences that specify leg development."

S: Yeah. So, this is full denial mode, you know, from the creationists. And of course, as always, they miss the point. The point is that evolution makes certain predictions. One of those predictions is as we look into the evolutionary past, we will find creatures that morphologically are between living creatures and the ancestors that they probably or must have come from. Snakes came from legged reptiles, therefore we must find snake-like ancestor creatures that have halfway-formed legs, and that's what we find, that that is the prediction of evolution. It's in the temporal sequence; it's in a morphological sequence; it's a validated prediction of evolution and there's just no way to avoid that.

R: Right, and you shouldn't be confused by the fact that this happens to be an organ that's going away in evolution, as opposed to an organ that's being developed. There's no difference there; there's no—it's not like they're dropping information as opposed to adding information; it's merely changing.

S: Yeah, it's just turning off the genes for the legs. They're just altering the way—how they get activated. I'm sure the information for legs is still probably mostly there, just not being activated or turned on. That's the whole "evolution can't produce an increase of information" thing, but of course there's other lines of evidence to show that yes, evolution can increase information. New genes, new structures can form over time. The thing that's so dramatic about the loss of structure is that you have something like a vestigial snake limb or hind leg that is too poorly formed to function for locomotion but has the leg parts that functioning legs do. If that was a structure that was used just for stabilization during copulation, why would it have the leg bits, you know? Why wouldn't it just be its own thing? So, vestigial structures like that give us that, you know, Q.E.D., that dramatic evidence for evolution that you don't get going the other way.

S: SGU 5x5 is a companion podcast to the Skeptics' Guide to the Universe, a weekly science podcast brought to you by the New England Skeptical Society in association with skepchick.org. For more information on this and other episodes, visit our website at www.theskepticsguide.org. Music is provided by Jake Wilson.


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