Evolution: The Scientific Evidence

[cheesehead]

Originally Posted by Zeta-Flux

What isn't entirely clear to many is that this is the process which leads to speciation.

When I first saw creationists' writing that they agreed that microevolution occurred, but not macroevolution, I didn't quite get it. There's no reason why the first could not lead to the second.

Now, I see that the idea of "kind" is very important to them -- if I understand correctly, they contend that no microevolution could change a species into a reproductively-separate one because that would be a (impossible) crossing of the boundary between "kinds".

But there's no scientific evidence for the creationists' "kind" phenomenon.

some speciation might be (and probably is) the result of

< snip >

intelligent interference.

But there's no evidence of that last alternative, if you're referring to the Intelligent Design theory rather than humans' selective breeding of domesticated species.

OTOH, there's quite a bit of evidence from psychology that some people want there to be a supernatural (and intelligent) parent-figure, and will go to great lengths to contend that that wished-for figure exists in reality.

[davieddy]

Cheesehead.
I appreciate how preoccupied you are with this thread, but is there
any chance of you acknowledging axn1's and my sorting out
of the error in your tortuous "solution" to the train puzzle?

David

[Zeta-Flux]

cheesehead,

Of course we can. Hosts with resistance conferred by genetically-transmitted properties will tend to have more offspring, so that genetic resistance will spread.

My point was that we do not know which genetically transmitted properties, in particular, will help an organism be resistant to an as-yet uncreated super-virus.

When I first saw creationists' writing that they agreed that microevolution occurred, but not macroevolution, I didn't quite get it. There's no reason why the first could not lead to the second.

Now, I see that the idea of "kind" is very important to them -- if I understand correctly, they contend that no microevolution could change a species into a reproductively-separate one because that would be a (impossible) crossing of the boundary between "kinds".

But there's no scientific evidence for the creationists' "kind" phenomenon.

I think you have begun to understand their position. I would disagree with your statement that there is no scientific evidence. Or, at the very least, these people claim there is evidence. Whether you or I agree with their use of the evidence is another matter.

But there's no evidence of that last alternative, if you're referring to the Intelligent Design theory rather than humans' selective breeding of domesticated species.

I would also include the creation of new genetic information in laboratories. And no, I wasn't speaking of the ID theory in particular.

[Zeta-Flux]

(Wanted to add: As I understand it, IDers claim scientific evidence for their theory. For example, irreducible complexity. Whether this evidence holds up to scrutiny, or establishes their theory, is another issue.)

[Prime95]

Originally Posted by ewmayer

Among any species, those individuals who possess some trait which gives them a better chance to survive and thrive in their local environmental milieu will consequently have a better chance of reproducing and thus passing their genetic traits on to succeeding generations.

One thing that has been perplexing me of late: homosexuality and evolution. Current belief is that homosexuality is a genetic trait rather than caused by one's upbringing. That leads to the troubling question: if homosexuality is genetic, what traits do homosexuals have that give them a "better chance of reproducing and thus passing their genetic traits"? It seems to me that evolutionary pressures would have wiped out such a gene.

My best guess is that it is either a recessive gene and/or part of a group of genes that do have beneficial traits and that most of the time when the male and female genes are mixed together the beneficial traits appear and much less frequently the homosexuality trait appears.

How do you explain the apparent paradox? Any ideas on what these beneficial traits might be? Any other thoughts?

[ewmayer]

Originally Posted by Zeta-Flux

then again some speciation might be (and probably is) the result of "wild" mutations, unusual pressures on a population, or intelligent interference.

Ok with (a) and (b), but (c) doesn't quite fit in here. One of the these thing/Is not like the other...

1) To date, there is simply no evidence that anything other than the above-described natural processes is required to explain *any* aspect of evolution and speciation, i.e "life on earth." This is far from saying that the theory of evolution - just like any other science dealing with immensely complex systems and many-varied "messy" natural processes - is "complete".

2) Just because we don't know all the answers (nor even many of the question) doesn't require us to willy-nilly go about inventing magical agencies to fill in the gaps in our knowledge. Such just-so invention is the province of religion and spiritualism, not of science.

3) Even if there were evidence - which there ain't - of something supranormal at work behind the scenes, busily designing away, you must admit any such "designer" would have some exceedingly curious properties, even judged by the kinds of "God can do whatever he wants" tropes commonly used by religionists. For example, despite the supposedly all-powerful (or at the very least all-clever) aspect which would be required to deliberately *design* even the humblest biological system, the Designer yet leaves glaring, massive flaws and suboptimalities littering the scene - the aforementioned genetic defects, along with the slew of other aberrations and things that go wrong (e.g. cancer and birth defects) and which cause untold suffering among their victims. Not to mention inside-out retinas, nipples on men, parasites, pathogens, you name it. Such a designer would be either far from "intelligent" (or maybe he's simply not a "details man"...) or would be one sick, sadistic f*** to pull stunts like that. Are you prepared to accept that, as you must if you want to believe in ID and not appear to be a colossal, cherry-picking, selected-evidence-ignoring hypocrite?

Oh wait, I believe this is where the religionists - erm, I mean, "intelligent design - and-yes-it-really-is-a-science-even-though-it-sounds-just-like-religion - proponents" inject yet another piece of wishful thinking into the gumbo, and come up with a "good designer" and and "evil designer" - let's abbreviate them GoD and ED for convenience. GoD is responsible for all the good ideas, but his naughty bastard half-brother ED just can't resist sneaking into GoD's workshop while GoD is asleep, and sabotaging GoD's best-laid plans, in such sneaky ED fashion that GoD doesn't realize this until it's too late and the latest model has already gone out the door. The Navajo called this guy Coyote, the Norse called him Loki, the Christians call him Satan ... whatever, but he/it ain't science.

4) As the above demonstrates, ID is, by its very nature, *not* science.

[MooooMoo]

Originally Posted by Prime95

One thing that has been perplexing me of late: homosexuality and evolution. Current belief is that homosexuality is a genetic trait rather than caused by one's upbringing. That leads to the troubling question: if homosexuality is genetic, what traits do homosexuals have that give them a "better chance of reproducing and thus passing their genetic traits"? It seems to me that evolutionary pressures would have wiped out such a gene.

My best guess is that it is either a recessive gene and/or part of a group of genes that do have beneficial traits and that most of the time when the male and female genes are mixed together the beneficial traits appear and much less frequently the homosexuality trait appears.

How do you explain the apparent paradox? Any ideas on what these beneficial traits might be? Any other thoughts?

My guess is that homosexuality is probably caused by a spontaneous mutation.

[Prime95]

Originally Posted by MooooMoo

My guess is that homosexuality is probably caused by a spontaneous mutation.

To me, it seems too prevalent (2 - 12% of the population(?)) for that explanation.

[xilman]

Originally Posted by Prime95

To me, it seems too prevalent (2 - 12% of the population(?)) for that explanation.

Perhaps an oblique comment may be illuminating.

Worker honey bees are infertile and have no chance of passing on their genes. Why, then, have infertile bees evolved?

Yes, you saw it here --- the Socratic method in action.

Perhaps human homosexuals provide a social role that enhances the likelihood of their genes to be passed on to offspring. From the genes' point of view, it doesn't matter that much whether the gene is passed on directly or from a close relative.


Paul

[ewmayer]

It's an interesting question. I would point out that there is as yet no unambiguous evidence that points to a clear *genetic* (as opposed to developmental) cause for homosexuality. We know that conditions in utero can exert a profound effect on many aspects of especially neurological/biochemical brain development, and the fact that gays are otherwise physically completely normal points to that as a more likely cause.

That of course still begs the question, just in a slightly different form: if there is an aspect of fetal development which is so prone to producing reproductively "challenged" individuals (in this case challenged by lack of inclination rather than ability), why would selective pressure not have reduced or eliminated this feature of in utero fetal development? I can think of 2 quite plausible possible reasons:

1) Since homosexuals are in fact reproductively capable, perhaps the basic biological urge to reproduce still exerted itself in evolutionary history to a great enough extent that overall reproductive success was not affected. That is rather vague, but there is a basic prediction that follows immediately, namely this: For this to be plausible, it requires that *bisexuality* should actually be a more common condition than pure 100% homosexuality - in other words, most individuals who feel significant sexual attraction to the same sex *also* feel sufficient attraction to the opposite sex that mating for reproductive purposes still occurs (or at least did over millions of years, on balance - religious proscriptions being a rather recent phenomenon) at something close to the normal level.

2) The percentage of homosexuals (which does appear to be appreciably > 0) whose attraction to the same sex is sufficiently strong as to effectively impair reproduction should still have the capacity to contribute enough to the survival of the group (we're talking especially small tribal groups, the kind that dominated human evolutionary history until very recent times) so as to compensate for their diminished reproduction. In fact there are many examples of this in other species: in wolves for instance, only a small subset of the pack are making the babies, whereas the others are helping in what are basically support roles. If Durk is a gay caveman (a "gayve-man" in modern PC-speak) who happens to feel nausea at the sight of a cave-gal, he might still be a really good hunter, protector and cave-babysitter. The latter skills help Durk's famously skirt-chasing cave-brother Thag have and successfully raise a big ol' passel of cave-children, more than he would have been able to had Durk been busy rearing his own kids. Durk's genes still make it into the next generation, but indirectly, as a result of his and Thag's sharing half their genes. Problem solved.

[Prime95]

Originally Posted by xilman

From the genes' point of view, it doesn't matter that much whether the gene is passed on directly or from a close relative.

That is a semi-plausible explanation. I suspect a gene would have to "work harder" to be passed on indirectly. That is, wouldn't a gene that increases an individual's survival rate by 10% have a better chance of passing itself on than a gene that increases your family's survival rate by 10% (or maybe not depending on the size of the family!)?

One could also argue that homosexuality reduces the average number of direct offspring but is balanced by some increase in the direct offspring's chance of survival.

Can mathematical modeling of evolution give us some clues? For example, take recessive gene diseases like hemophilia, sickle-cell anemia. If you assume it eliminates that individual's chance of passing on the gene, but unaffected family members still can, then a mathematical model would probably predict a low prevalence of the disease in the total population.

If models were good enough, you could adjust the "percent of homosexuals that pass on their genes directly" and "increased survival rates because of beneficial aspects of homsexuality", run the model and see which settings explain the current prevalence in the population.