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Proton -> RE: Lets talk evolution! (5/2/2008 5:15:22 AM)
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ORIGINAL: forstier
Being an old fart I can claim that they changed the rules {or assumptions} since I was in school and concede your point. Still, the non-reversion makes sense, particularly when we point to the total absence of new species in the past 10,000 years. The non-reversion requirement is tested {and may have been replaced by} a requirement that for a species to be defined, reproductive opportunity with its "cousins" must be absent.
I can only reiterate what I said before. Though all catalogs of species are a function of evolution, however, evolution itself is not a direct function of irreversible speciation. The latter is a contingent by-product of the accumulated environmental changes + genetic variation favored by natural selection, over an indefinite period of time. It is obviously a very good index for measuring evolution (i.e. our fossil records of diverse strata testify to evolutionary history), but it is not the primary rationale for it.
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And yes, most species arrive and dissappear in waves and not continuously over time. But, many species have arisen in a near continuous fashion.
True, and again, this is not a priori but simply a statistical correlation. Species can propagate and become more complex, they can remain unchanged, revert, or even get wiped out.
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I think but do not know that a major reason for the number of species is ecological. The survival of a species depends on an adequate environment favorable to its growth. As long as a particular ecological niche is well occupied, it is difficult for another species to develop unimpeded into it. There is a defined number of ecological niches in this world and they are generally not continuous {ie, water ends, land begins-different niche, forest ends, grassland begins -different niche, and yes some niches vary continuously into another with no real edge}. so, the millions of possible combinations of species is dratically reduced to the number of ecological niches available on any given planet. {Clarification - a single ecosystem can support large numbers of species {hence food chains exist within ecosystems}
My point was that there are a variety of changing factors that are effective.
Yes a niche promotes surivival, but only for those individuals who are genetically primed for it. So, introducing a new species to that niche is not going to cast them all out. Its simply going to skew selection of the gene pool, towards those that are maximally fit to adapt.
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Combine that with the fact that most combinations of biological attributes are not viable and offer no competitive advantage - five legged horses and three eyed fish do not gain sufficient advantage to overcome the cost of resources needed to support them. This acts as "friction" in evolution.
Again, we have to be specific. Generally speaking, a mutation is like a shot in the dark. But at some point, a few mutations will optimize survival for a particular environment (which frequently goes through changes and thus perturbs the 'mutational status quo').
One example is viruses which (under standard conditions) try to repel certain mutations that are lethal to them. Ergo, their genome naturally minimizes the frequency of that mutation. However, under exposure to certain biochemical predators, this same [normally] dangerous mutation is colaterally very vital for resistance and thus multiplies over just a few generations at an incredible rate of selection.
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