How does adaptation REALLY work?

[Phil_Saoud]

Originally posted by JDeMobray:
**“Natural selection is not random, nor does it operate by chance. Natural selection preserves the gains and eradicates the mistakes. The eye evolved from a single, light-sensitive cell into the complex eye of today through hundreds, if not thousands of intermediate steps, many of which still exist in nature (See R. Dawkins, “The Blind Watchmaker”, New York:Norton)” - Michael Shermer, “Why People Believe Weird Things”
**

Nobody has claimed that natural selection is random. It’s the mutations that are being selected that occur randomly.

As for those intermediate steps, my thinking is that many of them are useless without the later steps. Therefore, there would have been no reason to select them for survival. Of course, there’s no reason to select them for extinction either. Given the right sequence of events, the vertebrate eye could have evolved using only this process but the odds against it are astronomical. And yet we have eyes. Therefore there are probably other factors, as yet unexplained, at work. Many aspects of Lamarks work were probably correct and, to his credit, Darwin revised his “theory” several times to account for these.

I’m interested in seeing what “The Blind Watchmaker” has to say about this. (I’m also hoping that I won’t have to apologize to Ben the internet guy).

Thanks for the reference.

[JDeMobray]

Originally posted by Phil Saoud:
** As for those intermediate steps, my thinking is that many of them are useless without the later steps. Therefore, there would have been no reason to select them for survival. Of course, there’s no reason to select them for extinction either. Given the right sequence of events, the vertebrate eye could have evolved using only this process but the odds against it are astronomical. **

Okily-dokily, another source you might want to check out is Richard Hardison’s book, “Upon the Shoulders of Giants.” Among the interesting, and topical things he writes about, one in specific is a computer program.

We all know the old monkeys with typewriters trick, right? Well, the exact chance of a monkey at a typewriter randomly typing in “To be or not to be” is 26 to the power of 13 tries. (Lousy lack of superscript). However, by preserving every correct letter, and eradicating each incorrect letter, the process operates much faster. How much faster? Hardison documents an average of only 335.2 tries. It takes a computer less than ninety seconds (probably would take a monkey a little longer), and only about four and a half days to produce the entire play.

How is this relevant? Well, in both cases we’re starting with a known thing (the human eye, or Hamlet’s soliloqy and attempting to determine how many random tries it would take to produce it. But the tries, in neither case are really random; just like evolution, Hardison’s computer eliminates the “mistakes” and arrives at the target a whole lot faster.

Also, you’re making the assumption that some of the intermediate steps are useless. I would presume that if you’re willing to start with a single light-sensitive cell then each possible improvement, no matter how slight may provide an adaptive advantage. Let me again refer you to a more recent work, Richard Dawkin’s “Climbing Mount Improbable”, from 1996.

[Jois]

Hefty debate and not too crabby so far…

Not to start WWW3, but hasn’t the eye been reinvented three times by evolution?

Think about it, I’ll try for a source.

Good explanation, Coosa.

I think I’ll toss in this bit: Siamese cats can have solid colored fur in warm climates - the areas that get cold get colored fur as a reaction to being cold. Legs, ears and tail all respond to this temperature. Why that would be helpful to the animal I don’t know. But not every change is harmful or helpful.

Jois

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Are you driving with your eyes open or are you using The Force? - A. Foley

[JDeMobray]

Originally posted by Jois:
** Why that would be helpful to the animal I don’t know. But not every change is harmful or helpful.

**

Exactly! Mutants are not monsters. Most mutations are small genetic or chromosomal aberrations that have small effects - slightly different ear shape, a new shade of fur. Some of these changes may provide benefits to an organism in an ever-changing environment.

Moreover, Ernst Mayr’s theory of allopatric speciation demonstrates precisely how natural selection can work in conjunction with contingencies of nature and mutations to produce completely new species.

[coosa]

Thanks, Jois, although I probably shouldn’t have used the pointed allele as an example, since, as you pointed out, it is a temperature-sensitive mutation. The amount of pigmentation in the coat is affected by the predominant temperature during the molting season, when the new coat is growing in:

“If a Siamese is kept in a cool environment during themolting period, the new coat will be appreciably darker than the old. Conversely, if a bandage is applied to a small area of shaven skin, the new growth of hair under the bandage is white.” *Feline Husbandry: Diseases and Management in the Multiple-Cat Environment, Dr. Niels C. Pedersen.

I can think of two examples of independent evolution of the eye - the type we mammals have and the compound eye of the insect. What is the third?

Didn’t wings also evolve independently at least twice? In one instance in birds, and in the other in mammals (bats). And I’ve wondered if flying squirrels, sugar gliders, etc. might not be an example of wing-evolution in progress.

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I have a firm grip on reality - now I can strangle it.

[Jois]

My college biology says, " Eyes have evolved independently several times in the course of evolutionary history." And then doesn’t go on to make a nice list. In Dawson’s “Climbing Mount Improbable” he states, “It has been authoritativley estimatedthat eyes have evolved no fewer than 40 times, and probably more than sixty time, independently in various parts of the amimal kingdom. In some cases these eyes use radically different principles.” Chapter 5, p 138 paperback 1997. ::Gulp:: Now should I dare check how may times wings evolved?

Back to the text, it specifically mentions:
Compound eye of arthropods
Eye of the octopus
Vertebrate eye
The lack of more detail a kindness, I’m sure, to basic bioloby students.

Are you driving with your eyes open or are you using The Force? - A. Foley

[hardcore]

Wings evolved at least 4 times: Birds, mammals (bats), pterosaurs (pterodactyls) and insects.

To anyone who thinks Darwin had a problem with eye evolution, let me quote from the man himself in The Origin of Species:

Yet reason tells me, that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist; if further, the eye does vary ever so slightly, and the variations be inherited, which is certainly the case; and if any variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, can hardly be considered real.

If you think the odds of eye evolution are astronomical, then show me. Calculate it.

[Smeghead]

[tangent]

Originally posted by coosa:
While I’m not positive this is universal, female mammals are generally born with all of their eggs already present in the ovaries…This means there is a very short time during which DNA alteration can occur on the female side of the equation - any changes must happen during fetal development at the time the eggs are developing.

However, male mammals produce new sperm constantly, in the millions. There is a much greater chance of a male’s sperm being affected in some way, and this change being passed on to whatever offspring is the result of that individual sperm. “Radiation” is not the only source of mutation - ingested or inhaled chemicals of various kinds that exist in nature can affect normal sperm production, and there are also simple ‘copying errors’ - when millions of sperm are being replicated every week, occasionally something is going to get screwed up and come out a tad different. Ever think about the possibility that you menfolk are the primary source of genetic variance?

Sorry - this isn’t really on the main topic, but I wanted to respond to this.

I don’t think it’s this simple. Yes, egg cells sit in females longer than sperm cells sit in males. And yes, mutations caused by replication errors can only occur while the egg cells are in development. But while those egg cells are sitting there for all those years, plenty more mutations can happen - radiation, chemicals, whatever, can all act on that DNA.

Similarly, while there may be more chances to get replication-induced errors in sperm, they have a correspondingly shorter time to sit around and be bombarded by environmental insults. I would guess that mutation rates are about equal in sperm and egg. Well, if not equal, also not different enough to say that one gender is primarily responsible for variability.

Also, any given ovum is much more likely to turn into a full-blown organism than any given sperm, speaking purely from probability, which will greatly impact the equation.
[/tangent]
Thank you for your tolerance.