Evolution of vertebrate eyes

Posted 21 December 2007 by PZ Myers

A while back, I summarized a review of the evolution of eyes across the whole of the metazoa — it doesn't matter whether we're looking at flies or jellyfish or salmon or shrimp, when you get right down to the biochemistry and cell biology of photoreception, the common ancestry of the visual system is apparent. Vision evolved in the pre-Cambrian, and we have all inherited the same basic machinery — since then, we've mainly been elaborating, refining, and randomly varying the structures that add functionality to the eye.

Now there's a new and wonderfully comprehensive review of the evolution of eyes in one specific lineage, the vertebrates. The message is that, once again, all the heavy lifting, the evolution of a muscled eyeball with a lens and retinal circuitry, was accomplished early, between 550 and 500 million years ago. Most of what biology has been doing since is tweaking — significant tweaking, I'm sure, but the differences between a lamprey eye and our eyes are in the details, not the overall structure.

Continue reading "Evolution of vertebrate eyes" (on Pharyngula)

10 Comments

Mr_Christopher · 21 December 2007

What theory about the development of eyes do Wells and Dembski offer in their new IDC textbook? How do they explain the origins of the eye?

How do any IDC "theorists" explain the eye?

D P Robin · 21 December 2007

Mr_Christopher: What theory about the development of eyes do Wells and Dembski offer in their new IDC textbook? How do they explain the origins of the eye? How do any IDC "theorists" explain the eye?

Don't we already know? "The eye is too complex to arise randomly. The Designer did it." End of "discussion". 8^(

PvM · 21 December 2007

We shall soon see ID creationists ignore or deny the evidence while failing to provide a competing explanation.

What a scientific sham ID truly is.

PvM · 21 December 2007

Wells and Dembski on the eye

Choose a biological system that is too complex, and one can't even begin to calculate the probabilities associated with its evolution. Consider the eye. A widely held myth in the biological community is that Darwin's theory has explained the evolution of the vertebrate eye. In fact, the theory hasn't done anything of the sort. Rather, Darwinists have identified many different eyes exhibiting varying degrees of complexity, everything from the full vertebrate eye at the high end of the complexity scale to a mere light sensitive spot at the low end. But merely identifying eyes of varying complexity and then, as it were, drawing arrows from less complex to more complex eyes to signify evolutionary relationships does nothing to explain how increasingly complex eyes actually evolved:" The gaps between eyes of differing complexity become unbridgeable chasms once one begins to ask about the actual changes in genes, embryological development, and neural wiring that had to take place to evolve full-fledged vertebrate eyes from simpler precursors. Yet, instead of conceding that these gaps constitute disconfirming evidence against their theory, Darwinists strike a pose of invincibility: "Prove us wrong," they say in effect. "Show that it didn't happen that way." By so shifting the burden of proof, Darwin's theory trumps alternative theories every time.

As usual the authors seem to be presenting a good case for their ignorance of what science has to say about the evolution of the eye Of course ask them how ID explains it and the response will likely be that ID is not up to the task.

RJM · 21 December 2007

This "God of the Gaps" BS is really getting tiring. It reminds me of the old (related) saying about Creationism:

"Identify a gap in the fossil record, then find a transitional form that perfectly fits in the gap, and a Creationist will conveniently respond that there are now two gaps!"

Dale Husband · 22 December 2007

The eye is a perfect example of a form that looks intelligently designed at a glance, but a closer look totally demolishes that notion.

The vertebrate eye is wired backwards, with the optic nerve fibers on top of the cones and rods that act as light receptors. This makes no sense, and results a loosely attached retina that a sharp blow can detach easily and a blind spot that renders a part of the visual field useless. Only an idiot would have made such a rotten design. Which would explain why most Creationists seem to be idiots themselves!

Then there are the muscles of the human eye. There are six. A better design would have only three.

And what about the fact that many of us eventually need glasses and suffer from cateracts in old age?

Ichthyic · 22 December 2007

which is exactly why only cephalopods are intelligently designed (just check out the anatomy of THEIR eyes - no flaws), and the designer must be Cthulu or Dagon.

we're just random flotsam on the evolutionary ladder cephalopods are gradually climbing before becoming masters of the universe.

PZ knows this, and not so subtly keeps hinting at it on his blog every friday.

PZ Myers · 22 December 2007

Then there are the muscles of the human eye. There are six. A better design would have only three.

That isn't right. You've got three axes of rotation, and you need opposing pairs of muscles, so six pretty much is the optimum number...although you could make a case that rotating the eye about its central axis is not a necessary function, so the superior and inferior oblique muscles are a bit redundant.

Ichthyic · 23 December 2007

[quote]although you could make a case that rotating the eye about its central axis is not a necessary function[/quote]

oh no, being able to roll my eyes at creobots is quite a necessary function.

hey, maybe that IS evidence of intelligent design?

Lab Lemming · 2 January 2008

PZ says:

"...in the pre-Cambrian... (snip) ...between 550 and 500 million years ago."

One of the wonders of radiometric age determinations is that they allow us to learn that the Precambrian ended 542 million years ago. Thus the dates that you give above are mostly inconsistent with your Eon.