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The Wandering Eye (Pleuronectiformes, We Hardly Knew You)
July 10, 2008 5:33 AM   Subscribe


 
Evolutionary biologists have floundered to explain how bottom-dwelling, carnivorous flatfish, such as flounder and plaice, evolved to have both eyes on one side of their head. Previous analyses of fossil evidence concluded that the change was abrupt.

What. I thought these were evolutionary biologists. What respectable evolutionary biologist proposes abrupt, massive, non-fatal morphology changes?
posted by DU at 5:41 AM on July 10, 2008


If you hit the first link and scroll down, there are a couple of good video clips.

This post isn't meant in a "IN YOUR FACE, CREATIONISTS!" way (although many of the news stories I'm linking to do use that angle). Although, I'm sure that phrase would have popped into the minds/mouths of several people who have had to debate this subject (flatfish were often used by Creationists to back up their argument).

Anyway, I was going for "Wow, isn't Natural Selection amazing (and completely irrefutable)?"
posted by chuckdarwin at 5:43 AM on July 10, 2008 [1 favorite]


DU, I think they just lacked evidence in the fossil record... until now.
posted by chuckdarwin at 5:43 AM on July 10, 2008


Impossible, since Good Science knows the earth is only about 6,000 years old.
posted by Rykey at 5:49 AM on July 10, 2008


I'm no expert, but it seems like "this creature appeared as a major new form in a single huge leap from an old one" would be a sufficiently extraordinary claim to require better than a poor fossil record to support it.

Anyway, at least it's cleared up now. The sideways flatfish really offend my engineering instincts. If you want to be flat, do it the right way, you bastards.
posted by DU at 5:59 AM on July 10, 2008


Evolutionary biologists have floundered to explain...

They just couldn't resist the pun.

But yeah, it was the explaining that was the problem -- absence of record, as Mr Darwin Himself noted -- not the understanding of it.
posted by rokusan at 6:05 AM on July 10, 2008


DU writes "What respectable evolutionary biologist proposes abrupt, massive, non-fatal morphology changes?"

Uh... the same ones that end up world-famous, get jobs at the American Museum of Natural History and teach at Harvard?
posted by caution live frogs at 6:06 AM on July 10, 2008 [6 favorites]


(All my dissertation proved was that I could write a dissertation. Maybe I should have studied fish instead of mammals?)
posted by caution live frogs at 6:07 AM on July 10, 2008


Perhaps the problem is the word "abrupt". If they are using it to mean "within a generation or two" that's just unpossible. If they mean it as "in only a few thousand years instead of a few million" well maybe.

But wait, the article actually semi-defines what it means: But reexamination of ancient fossils now supports the hypothesis that the flatfish eye position actually evolved over thousands to millions of years.

So the previous hypothesis was that it was faster than "thousands of years"?

And btw, Gould agrees with me, which is helpfully illustrated by your own quote: Punctuated equilibrium is therefore mistakenly thought to oppose the concept of gradualism, when it is actually a form of gradualism, in the ecological sense of biological continuity. This is because even though evolutionary change appears instantaneous between geological sediments, change is still occurring incrementally, with no great change from one generation to the next.
posted by DU at 6:13 AM on July 10, 2008


I had thought so all along
posted by Postroad at 6:25 AM on July 10, 2008


"Scientists had long assumed flatfishes must have arisen suddenly because they could not imagine the adaptive significance of intermediates, but this work delivers clear evidence that such intermediates did exist, and therefore, that flatfish asymmetry arose gradually."

Natural selection doesn't demand "adaptive significance". It is a measure of reproductive fitness and that's it. There not need be any more reason than other fish found the googly-eyed freak you know kinda cute.
posted by three blind mice at 6:40 AM on July 10, 2008


Evolution not only is happening with each new generation but every minutes of every day. The idea of a static species is an illusion. Well illustrated in the Pulitzer Prize winning The Beak of the Finch. It's still an idea most people can't grasp as it goes against common sense sensory experience.
posted by stbalbach at 6:52 AM on July 10, 2008


That's a good point, three blind mice, and highlights one of the weak points of the fossil record: the inability to show links between structures and behaviors. We can often make educated guesses, as in the case of Parasaurolophus, but we really won't ever know precisely how some ornaments and things were used. It seems that the study of the fossil record in this case suffered from a lack of imagination more than a lack of evidence; earlier paleontologists couldn't imagine how the asymmetrical eye positions would "work", and may not have been intellectually receptive to the idea that specimens in their hands represented transitional forms. In their defense, they didn't have CT and so on.
posted by Mister_A at 6:54 AM on July 10, 2008


But, as the Beak of the Finch notes many times, a lot of this "evolution" cancels itself out. A year of drought results in bird beaks like THIS but a year of plenty results in bird beaks like THIS amirite. It's like brownian motion. Within a certain epsilon, the species is pretty static.

It's when evolution is being driven consistently in a particular direction that you get major changes. And it actually can happen really fast. I don't remember the exact numbers, but you can theoretically evolve an elephant-sized mouse in some number of hundreds of years by just having each generation be 1% larger than the parent. (Someone should get on this.)

The problem with applying that to a flounder is that we aren't talking about some relatively simple "just make everything a bit bigger" mutation. Wouldn't there have to be multiple coordinating mutations to change the behavior, embryology, etc of this animal? All at once?
posted by DU at 7:00 AM on July 10, 2008


DU - I always understood punctuated equilibrium to mean that a slow buildup of genetic changes over time creates the potential for speciation, but that speciation occurs in a relatively short period (geologically speaking) due to a combination of environmental factors and genetic diversity. No environmental change or low genetic diversity, little chance for speciation; when both are present speciation is likely to occur rapidly.

Physical specimens such as fossils do not necessarily reflect genetic diversity, the propensity for change. I highly doubt that any evolutionary biologist would propose an abrupt change in any sense other than the geological timeframe, but pop culture interpretations of the "abrupt change" statement are nearly always going to assume this means change within a generation or two.

Of course, punctuated equilibrium is a fairly old idea by now, and it's been somewhat discounted since the initial proposal.
posted by caution live frogs at 7:16 AM on July 10, 2008


Remember, equilibrium ≠ stasis.
posted by Mister_A at 7:18 AM on July 10, 2008


I highly doubt that any evolutionary biologist would propose an abrupt change in any sense other than the geological timeframe, but pop culture interpretations of the "abrupt change" statement are nearly always going to assume this means change within a generation or two.

I agree, but the article specifically calls out "thousands of years". OTOH, this would not be the first example of a popular science article being partially inaccurate *cough*completeBS*cough*.
posted by DU at 7:24 AM on July 10, 2008


I highly doubt that any evolutionary biologist would propose an abrupt change in any sense other than the geological timeframe, but pop culture interpretations of the "abrupt change" statement are nearly always going to assume this means change within a generation or two.

Evolution can work remarkably quickly. Lizards introduced to an island off Croatia developed cecal valves (a novel structure) within some 40 years. See this National Geographic article.
posted by colophon at 3:44 PM on July 10, 2008 [2 favorites]


I found a reference for DU's comment: "evolve an elephant-sized mouse in some number of hundreds of years by just having each generation be 1% larger than the parent" -- it would take about 20-100,000 years.
posted by shavenwarthog at 2:28 PM on July 11, 2008






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