Cutting Through The Crap

Thursday, March 17, 2011

Eye Ball


For my countless readers who disbelieve evolution but whose curiosity and desire for truth allows them to go where the facts take them, I offer this.

Fact-deniers love to point to the human eye as proof of intelligent design: such a thing could never have evolved. So here's a discussion about a recent scientific paper on the subject of eye-evolution. It's fascinating, detailed, and complex. It requires a certain level of reading comprehension and is not easy as pie. It also demands the ability to question one's neediness. Which explains why such thought is never part of the creationist discussion, or, when it is, is completely misunderstood. A sampling:

About 600 million years ago, or a little more, there was a population of small wormlike creatures that were the forebears of all modern bilaterian animals. They were small, soft-bodied, and simple, not much more than a jellyfish in structure, and they lived by crawling sluglike over the soft muck of the sea bottom. We have no fossils of them, and no direct picture of their form, but we know a surprising amount about them because we can infer the nature of their genes.

These animals would have been the predecessors of flies and squid, cats and starfish, and what we can do is look at the genes that these diverse modern animals have, and those that are held in common we all inherited together from that distant ancestor. So we know that flies and cats both have hearts that are initiated in early development by the same genes, nkx2.5 and tinman, and infer that our common ancestor had a heart induced by those genes…and that it was only a simple muscular tube. We know that modern animals all have a body plan demarcated by expression of Hox genes, containing muscles expressing myoD, so it's reasonable to deduce that our last common ancestor had a muscular and longitudinally patterned body. And all of us have anterior eyes demarcated by early expression of pax6, as did our ancient many-times-great grandparent worm.

[...]

There's another thing we know about these ancient ancestors: they had two kinds of eyes. ciliary and rhabomeric. Your eyes contain ciliary photoreceptors; they have a particular cellular structure, and they use a recognizable form of opsin. A squid has a distinctly different kind of photoreceptor, called rhabdomeric, with a different cell structure and a different form of opsin. We humans also have some rhabdomeric receptors tucked away in our retinas, while invertebrates have ciliary receptors as well, so we know the common ancestor had both.

Now this ancestral population eventually split into two great tribes, the protostomes, which includes squid and flies, and the deuterostomes, which includes cats and starfish. It should be an obvious indication of the general state of that ancestor that it represents all that those four diverse animals have in common. It also tells us that while that ancestor had eyes, they were almost certainly very simple, and could have been nothing more than a patch of light-sensitive cells, or perhaps even single cells, as we see in some larval eyes ....


I find it fascinating and thrilling. Contemplating this amazing process is exhilarating and, yes, spiritually rewarding. What an amazing planet we live on, how singular and powerful the forces at work. It makes our lives all the more valuable, our surroundings all the more wonderful to behold. For a nice diversion from nuclear holocaust and general disintegration of political thought, I recommend taking the time to read it. Just for the hell of it.

1 comment:

Joseph from Montana said...

You city guys are so smart, you reallly are. How worms evolved and folks came next. I'd ask you to visit Montana, but you might get killed if you opened your mouth in Bozeman BBQ Bill's Bar. Next time you fly over, drop me a note and I'll let you kick a heffer or brake a young buill.