A Question About Evolution

[vhawk01]

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Most of these responses seem to interpret the OP differently than I did. Leaving aside the question of 'humans as a species', I did pause for a second at the fact that all species are fairly well defined. I mean, you can look outside and see 10 different species of birds, and they all have their own unique coloration....why don't goldfinches range continuously from bright yellow to dull orange, for example?

A little thought leads me to this (probably obvious) conclusion...right or wrong?

Successful genes are propogated by mating with individuals that are most likely to share the majority of those genes. This results in a clumping effect...If I'm a yellow bird, I'll try and mate with another yellow bird, even if i COULD mate with the orange bird, because the yellow bird is more likely to share my genes. This results in a pressure towards a very narrow set of genes. Obviously, there is some countervailing pressure in that SOME variability is required (hence, incest is a no-no [img]/images/graemlins/smile.gif[/img] ). In general though, If you started with an 'ill-defined' species, consisting, say, of birds that varied in size and color but were otherwise genetically identical, the population would tend towards a single set of characteristics over time...

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It would trend towards that single set (although thats probably simplistic, it works fine for now) because those animals all live in the same niche. The niche is what defines the selection pressure, so it stands to reason they would have the same characteristics. But even so, imagine a scenario in which you have a population of birds that look something like parrots. Now, some small subset of this group leaves and finds a new niche. After a couple million years, due to the drastically different niche, they now look something like toucans.

But we know that no parrots ever had kids who looked like toucans. Truly, every intermediate body shape between the two (and not just body shape, obviously) DID exist. But where are they now? They are lost to time, but they absolutely DID exist. Had the selection pressure reached a sort of equilibrium at a different time, or if we were simply viewing them at a different time, we would see exactly some animal 'halfway in between.' If we are lucky, perhaps some of these fossilized, but its extremely unlikely.

So, your point explains why all LIVING members of a species share a similar set of characteristics, but it doesn't explain how we got from parrots to toucans with nothing in between. At each snapshot of time, your explanation can tell us that the population would look the same, but in order to understand why only the two extremes exist today, you have to understand that the gradients exist chronologically, as was mentioned earlier.