A Question About Evolution

[Hoi Polloi]

Extinction per se is evolutionarily neutral, that is, Neanderthals didn't die out because they failed to evolve. That's putting the cart before the horse or donkey or mule.

Other than that I think this is okay.

[Hoi Polloi]

The ring species examples raised by other posters provide an interesting correlate insofar as they represent a kind of spatial approximation of what we think of normally as occuring chronologically. Ring species are in that gradient gray-zone between species and not-species by the classical definition of reproduction, but they demonstrate that there are gray areas there and that finally species is not a full-stop boundary.

Your main point, that things are not tidy, is most important. A "complete" fossil record would in theory provide the "gradients", but fossilisation is a fairly rare occurence so we are lucky to have as much there as we do.

[Lestat]

Very good explanation Bill!

[Justin A]

Thanks that's a big help.

Would it be fair to say that early hominids don't exist currently because of competition? That is to say that they were not able to keep up with humans, but primates that are still around today don't have to compete with humans?

[ChrisV]

No, probably not. It is possible that early hominids were wiped out by warfare with more advanced humans, but at the time their extinction took place, there should have been enough space for the species to coexist. More likely is that they were eliminated due to good old natural selection - that is, they just weren't good enough to survive.

The fact that there are only a handful of species on the planet that use high intelligence as a survival trait - and only one that does it to the extent of H. Sapiens - is probably a hint that there is something problematic about this survival strategy. The human brain consumes about 20-25% of the body's total energy input. That is a hell of a lot to spend on a bit more smarts when you could spend it running faster or being stronger. Chimps, for instance, direct a lot more of their energy to strength than we do - an adult chimp is HUGELY stronger than an adult human.

My feeling is that there is kind of a "hump" of diminishing returns that is hard to get over - that for a long time, increased intelligence doesn't return much survival EV, and then suddenly, boom! it returns a whole heap in one go. The development of complex language is a good candidate for a "tipping point" where suddenly intelligence becomes a huge asset. Once we fluked our way over this hump, suddenly slightly more intelligent humans had a huge survival advantage over others. This would explain why we are vastly more intelligent than other primates. Descent from the trees was probably a factor in sending us in the direction of higher intelligence in the first place, since there was energy spare that no longer needed to be spent on upper body strength for swinging through trees.

Note: This is just my personal theory. I have no expertise in the field.

[Jasper109]

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Very good explanation Bill!

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[arahant]

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...

[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.