Wednesday, March 21, 2012

Yes you DO get loss of genetic diversity with evolution Part 10

Draft to be changed as I can get to it.

[Faith]Consider the dog example while we're at it. Every breed of dog MUST show reduced genetic variability compared to its population of origin because if you want it big you're going to have to eliminate everything that tends to smallness, if you want it good natured you have to eliminate everything that breeds for ferocity, and so on
[Subbie] This is only true if the "first dog" had all possible dog genetic information, and subsequent dogs were created by taking out all the stuff that wasn't necessary for that breed of dog. This idea is ridiculous.
The first dog doesn't usually display a perfect collection of all the desired traits a breeder is seeking, just a tendency. Breeders select animals for the traits they desire. If they want bigness they breed with big dogs, if they want sweet natures they breed the sweetest ones in the litter, trying to IMPROVE the particular trait they are interested in, selecting those individuals from subsequent generations that have the best expression of that trait. They chose the original dog because it had such a trait but its descendants are selected to improve on it. Then they breed it with other dogs with the same trait. You don't need ALL original dog traits, just dogs that have the trait you want. When an unwanted trait shows up they are careful to keep that animal from breeding. Over time the traits they are seeking become established and the ones they don't want get eliminated. This is elementary my dear Watson, no doubt highly oversimplified (you don't usually get a single trait without a company of other traits along with it for instance) but nothing at all ridiculous about it.

Then Taz:
[Faith]A nearly obliterated population such as the seals which were hunted to near extinction, may actually come back in large numbers, but they will come back with much reduced genetic variability compared to their original population. Surely this is obvious?
[Taz] No, it's not obvious, because you are using it in the wrong way. It's like saying each individual atom of my computer is colorless therefore my computer is colorless. There's a fallacy for that. Try to guess what it is. While it is true that the seal population came back with less genetic variation than before, we're talking only a couple generations. You are trying to apply a couple generations of seal as an example of evolution. If I didn't get drawn in by your honest tone, I would have said strawman.

What happened with the seal population you described is called a bottleneck, where an event triggered a loss of many traits and the resulting allele frequency is completely different than the one before. In this particular case with the seal, the event is called over-hunting.

Because we know for a fact that each individual in that population carries at least several mutations compared to its parents, if left undisturbed it is inevitable that genetic variation in that population will increase given enough time. By enough time, I'm talking about at 50 generations or so, not a couple.
And again we are denying the obvious to focus on the nonexistent savior of evolution, (beneficial) mutation, and the unprovable effect of lotsanlotsanlots of TIME. Again, built in alleles are quite enough to produce a huge array of variations in most species, while mutations contribute nothing but death to the mix (yeah, even the "neutral" ones whose effect is simply invisible). And that's all they are contributing to these genetically depleted seals too, not a stepping stone to further evolution but the threat of extinction.

And again, even if mutation did contribute viable new alleles, alleles only vary existing traits, what you need is new traits, new "information" at least whole new genes.
[Taz]As a side note, the rattlesnake population in the southwest are going through a bottleneck event as we speak. People there are hunting down every rattlesnake they could find, which are usually the ones that make a lot of noise. The very trait that helped keep their ancestors from being trampled on are now working against them with humans. There are reports of increasing number of silent rattlesnakes crawling around. Goddamn rednecks...
Yeah, they've selected silent rattlesnakes, what's your point? If they keep it up they'll eventually eliminate ALL the genetic possibilities for noisy rattlesnakes -- which is what ultimately happens with all selection events.
[Taz]I'm sure that one day in the distant future, our children's children will label this period as the great bottleneck era for most species on Earth. Man has been changing and molding population genetics to our liking. I'm sure we'll look back one day and realize the vast changes we've made to wild populations everywhere.
Could be, selection happens by many means and human interference is one of them. What you and others who are in thrall to evolution refuse to consider is that such a bottleneck IS evolution -- big changes in this case, just the stuff of evolution, and it DOES come to a screeching halt because of genetic depletion -- it's just that the whole scenario -- striking new traits plus serious genetic depletion -- happens a lot faster than the usual processes of variation. These normal processes, just like bottleneck, all involve some form of reproductive isolation of a portion of the main population that brings about new gene/allele frequencies. This isolation can occur in many ways, such as migration of a random assortment of individuals, a reproductive preference pattern within a population, natural selection having to do with environmental pressures, and so on. Bottleneck just does it faster.

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