Pages

Tuesday, April 8, 2008

A Fish-eyed View


Yesterday, I got into a discussion(or should this be pseudo-argument) about vestigial fish eyes and holes in Darwinism with my husband.
A few weeks ago, he had talked about 'Mutations cannot be random, they have to help the organism adapt to its surroundings better', while my understanding was that, mutations were random, and the ones that enabled the animal to survive its environment better were the ones that would be propagated down the generations. But arguing with S is somewhat like waving a red flag at a bull. So I held my peace.

Yesterday, he brought it up again, this time adopting my original contention as his baseline, and trying to cast me as opposing it.
He said: "I've been reading about Darwin's theory on a very good website. I've a better understanding of it now."
Me: "Which website?" ( Hoping it was not some creationist leaning site)
Him: "Stanford University, I think" (Me: inner sigh of relief)
Him: "I have a problem with some holes in Darwin's theory though. Why would fishes lose their eyes in a dark cave, when it isn't an adaptation that benefits them directly? The presence or absence of eyes shouldn't really matter in such a situation, so why should they 'lose' the eyes they may have had originally?
Me: Maybe the loss of eyes was tied to some other change that improved their chances of survival, that we don't know of yet.
Him: That doesn't make sense.

Yadda...yadda...yadda for the next half hour.

And so it continued today over Skype chat.

Me: Why Do Good Eyes Go Bad?

Cave-dwelling tetra fish (Astyanax mexicanus) are blind; they have small vestigial eyes that do not work. Then why have them at all? Biologists have long struggled to explain how natural selection could fully account for such degenerations, and recently they have found another possible answer: genetic mutations that hamper eye development also may increase the number of taste buds. Thus, mutations that happened to give the fish an advantage in tasting and smelling—a huge benefit in a dark environment—might also have inadvertently, and harmlessly, caused the degeneration of their eyes.

Him: Man, that sounds fantastic "genetic mutations that hamper eye development also may increase the number of taste buds"!!
Me: Some tradeoff. But does this answer your question?
Him: No, it is too fantastic.
Me: You didn't seem to believe my argument yesterday.
Him: Not this either.
Me: Contrary is always difficult to believe... You can say bats have poor eyes so the species that devised sound to navigate had a better chance to survive... that is believable.
(Er...isn't that what the last line of the paragraph(highlighted in green) saying?)
Him: But [the] contrary is hard to digest... [i.e] better sound sensitivity hampered eyesight (like in this case developing better taste bud hampered eyesight)
Me: What I mean is that this line of argument: that some other unexplained factor that conferred greater advantage but led to vestigial eyes, won the day. You were dismissing that offhand. Maybe these biologists haven't found the right thing yet, but the possibility cannot be ruled out.
Him:I am not ruling out... hard to accept that explanation is "scientific"
Me: Why?
It's still a hypothesis that could explain, provided they are able to prove it holds through observation.
Him: I accept it as hypothesis but not as proof or even a "substantiated" theory.
Me(and I really need to get my blogging done) : That's good. At least you accept it's a valid if unproven hypothesis.
Him: Yes.
Me: Let me put it this way: it's not implausible that improved sense of taste and smell that resulted due to a random mutation, but also rendered the eyes less usable, was a trait that improved the fish's ability to survive and reproduce in the dark cave.
So some several generations later, we have the vestigial eyed fish in the dark cave, and normal 'control' species they were derived from in a lighted environment above the dark cave.
Me ( now in must-have-last-word mode): Regarding vestigial features as interpreted by Darwin.
Him: I have a call now.

From the link I last sent him, I found the explanation for his interpretation of what 'vestigial' means.

Those who question the existence of vestigiality usually claim a different definition for vestigial, giving a strict interpretation that an organ must be utterly useless to qualify.[19] This is a definition often used in dictionaries[20] and children's encyclopedias.[21] Biology textbooks[22][23] and scientific encyclopedias[2] usually describe an organ as vestigial if it does not serve the same function in the modern animal as the cognate organ served in an ancestor, even if the modern organ serves a completely different use (preadaptation).

Those who consider the true meaning of vestigial to be "completely without use" tend to claim that the meaning has been changed over time as structures thought to be vestigial were found to have other uses.[24] However, documentation indicates that from the theory's beginnings in the 19th century, vestigial structures have invariably been understood to "sometimes retain their potentiality"[6], becoming either "wholly or in part functionless".[25] It was thought that "not infrequently the degenerating organ can be turned to account in some other way".[26]

No comments: