[quote]Varqanir wrote:
[quote]Sloth wrote:
Where does reproductive isolation come in with a man born with no legs? If all the legless people got together as a population, and the leg-endowed another, are they somehow unable to interbreed and produce fertile offspring?
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Natural selection is pretty straightforward. If you were a nerdy religious guy who only ever spent time in the library or at church, the odds are better that you would select as a mate the nerdy girl at the next table or in the next pew over the party girl who never picked up a book or a bible in her life. The odds are also good that your children would also be bookish and pious, because that is the culture in which they are raised.
In nature, if you are a finch living in the Galapagos Islands, and you got your food by picking insects out of the bark of trees, the odds are excellent that you would select a mate from the female finches who also pick insects from the bark of trees, and not waste your time trying to attract those weirdo finches who eat bugs off the ground. Your children would eat the insects on the trees, and so would their children and their children’s children.
You could theoretically mate with one of the ground-feeding finches, and your offspring would still be fertile, if a bit conflicted over where to go out for dinner.
Speciation doesn’t necessarily guarantee mutual infertility. The more we learn about speciation, the more it looks like species are simply groups of animals that look different enough, and have specialized “job descriptions” different enough, to be able to be taxonomically distinguished from other groups of animals. But different species of plants cross-pollinate all the time, and different species of birds can certainly interbreed if an individual from a completely different environment is introduced into a new habitat.
The only reason lions and tigers and bears (oh my!) don’t typically interbreed is because their habitats are geographically divergent. Polar bears don’t typically share habitat with brown bears, but they sometimes do. And hybrids of these two species have been observed in the wild.
Lions and tigers, while less dissimilar than polar and brown bears, are nonetheless instantly recognizable as different species. But both are large carnivores in the same genus, and although their ecological niches seem very dissimilar–lions hunt in packs in grassland during the day, tigers hunt in forests alone at night-- this is not always the case. Hybrids of tiger and lions are now relatively commonplace, and these hybrids (ligers and tigons) are not all infertile. Given a shared habitat, and enough time, natural hybrids would certainly appear, and eventually adapt to a new niche (referred to by the lions as “daywalkers”, no doubt), and by definition, a new species.
As for our limbless torso people, the pressure toward reproductive isolation would come both from outside the population (limbed humans being less likely to select one of the torso people as mates), and from within (torso people are more likely to select other torso people, if given the choice). If given enough time (and we’re talking hundreds of generations here), we could very well have a situation where limbless people only mate with other limbless people, especially if, as in my scenario above), limblessness confers no disadvantage, and in fact confers definite advantages. Could the limbies still interbreed with the torsoids? Probably. But as the two niches (species) would have by then so completely diverged in behavior and morphology, it would be extremely unlikely.
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I actually do know this. But what does it have to do with a human being born without legs? That was where we started. I mean, I get that a reproductively isolated legless population, with passage of many generations, and with a compounding divergence of trait selection (due to the isolation), might end up experiencing speciation.
Then again, if a legged trait pops up in that population, back to bipedal locomotion.
