Monday, November 1, 2010

Evolution as Fact Addendums

I cross posted my fairly mild (for me) discussion of evolution over at Book View Cafe Blog. You can see it here.

There was one predictably difficult comment about issues people had with evolution as a fact.

I responded and here are my responses.

Paraphrased: What are the foundations of evolution as the origin of speciation?

A “species” has at its heart effective reproductive isolation such that selection can act upon a group without being compromised by outside genetic input. There was a frog I learned about in college (whose species name I do not recall) that lived in two locations, at the canyon rim of the site and in the canyon valley. The two animals appeared to be physically identical. However, upon close examination the they did not appear to interbreed. Even in the laboratory. Investigation revealed that one of the groups (I forget which) was making its call at twice the rate of the other. This effectively reproductively isolated it. Subsequent investigation showed that the “quick” frog group had undergone chromosome doubling– rare in vertebrates but it does happen. Consequently, it was now reproductively isolated from the parent group. The discussion at that time was whether this was a new species or a sub-species, since it appeared to be physically identical. I would argue that the intransigent nature of the reproductive isolation (it’s pretty unheard of to un-double a chromosome) made it a species. Regardless, now the new group could be selected against without the effect being diluted by influence from the parent group.

There’s an interesting faq about speciation here:

The NSF also has a good evolution section and here are some articles about it:

Paraphrased: I'm having trouble with an explanation of how everything go there by accident, especially us. Scientifically speaking, I've see no significant evidence of it.

Just some small additional points: evolution is the model for how organisms changed over time from the point at which natural selection could occur– once life began, for example. No one has a good model of how life began and until that occurs no one can say what role natural selection played. The natural selection model applies extremely well– to the point of “scientific theory”– once life occurred.

Second, no reputable scientist will ever say that a given organism got here “by accident”. Evolution is not an accident. Evolution results from circumstances presenting an opportunity for the natural variability of organisms to make a difference in reproduction. If there is an advantage to being fast in the animal’s circumstances that animal is going to breed more effectively and pass on that trait to its offspring. There is *nothing* accidental about that.

There is chance and circumstance at two ends of the selection process. The variability present in animal populations is one arena where changes that have a random character to them occur. Even this over time can have less randomness than one might first think. Cuttlefish, for example, have a variability within their reproductive strategy. One subgroup has a battle for dominance approach to win over a female. Another sneaks in and makes itself look like a female until it can present itself for mating. *Both* strategies occur in the same population. That sort of variability has been preserved.

The other area that is more truly random is the nature of the surrounding circumstances– the ecology and physical surroundings of the organism. But here, too, animals can adapt to each other as well as to the physical environment, thereby altering odds in their favor.

But the randomness of the physical geography over time also has an influence. One of my professors said that you only really know an organism if you can observe it over a few tens of thousands of years. Because the organism that is presented to you isn’t just the organism that succeeded in the environment you’re observing it in, it’s the organism that survived all of the droughts, rains, ice ages and meteor strikes prior to the environment you’re observing it in.

Finally, I think the crux of the problem isn’t other animals; it’s our own evolution that matters to us. The descent of man is pretty well worked out now in that the basic sequence of species is known. What we don’t know (at least I don’t think we know. Others probably know more) are the selective pressures that caused the changes.

And then *Something Happened* about fifty-to-eighty thousand years ago that put us on the trail to where we are now. We don’t know what that was. Whatever it was it hasn’t seemed fossilize.

But that species fifty thousand years ago did become us. Not through any set of random events but by winnowing out those who *weren’t* us and mating with those who became us. Again, the selective pressures are obscure though there is some interesting work coming out of South Africa suggesting we started eating fish.

For reasons that are difficult for me to understand it is hard for a lot of people to accept “Man still bears in his bodily frame the indelible stamp of his lowly origin.” We are tremendous beings. And that magnificent heritage is the result of thousands of decisions of people over thousands of years. How could we possibly expect those decisions not to help form who we are? And if those decisions are pushed back far enough how could we not expect those that made them would not be human?

Personally, I find this a wonderful idea. It says, concretely, we came from somewhere through the actions of those much like ourselves. It says we’re going somewhere; that our actions and decisions bear long term consequences not in some hereafter but here, now, and in the future. It gives heft and meaning to what we do right now in the physical world around us. We are responsible for what we do and what we do matters. As did the actions of Ogg, fifty thousand years ago, sitting out in front of a cave in South Africa, watching the fish jump and wondering if they were good to eat.

No comments:

Post a Comment