Actually, not always. Many times *both* survive.Originally Posted by [b
Imagine you have one population, and suddenly a river splits the habitat in two, separating it into two populations (assume it's something small, which can't cross the river). One side of the river becomes plains, while the other is forest. Faced with different selective pressures, they evolve in different directions, and eventually they couldn't interbreed even if they river dried up and they both intermingled. Each spreads throughout their habitat, becoming two new species.
This happens all the time, and sometimes doesn't even require geographic separation; it's especially common in parasites who jump to a new host. The colonizers evolve to suit the new host, and soon there are two species in the same range, one on each host species.
Of course, then things like asteroids happen, but that's a whole different ball of wax.
Why? Our DNA isn't similar, it's almost totally identical. We have a chain of fossils going all the way back.Originally Posted by [b
But more important than the genes are what's *wrong* with the genes. See, viruses insert their DNA in cells in order to make copies, but every so often, something goes wrong, and the DNA of the virus gets damaged and can't replicate. It simply inserts into the organism's DNA, fails, and stays there, passed on with the rest of the real genes.
Chimps and humans share the same dead virus parts, in *precisely* the same places (though some are unique to each lineage, aquired after we diverged). Similarly, Chimps and humans share some, but not all of our dead viri with gorillas (indicating a slightly more distant ancestry). So on and so forth.
Is there *really* any other plausible explanation for why we inherited the same dead virus parts in the same places with the same disabling mutations, other than that the virus infected our common ancestor, failed, and got 'stuck'?
And before you ask, yes, they are real virus genomes; we recently 'ressurected' one, using data from human and ape genomes to reconstruct a *viable* virus that infected our ancestor 5 million years ago.
Not really: why does all life work the same, at the molecular level, otherwise? There's no reason things *must* work the way they do; there's tons of plausible chemical alternatives. Yet we *all*, from bacteria to Bob Smith down the road, read the DNA code *precisely* the same way. Why, if not common descent?Originally Posted by [b
Why do all living things use the same 20 amino acids? There's many, many more than 20 amino acids that are chemically possible, but *ALL* life uses the same 20.
Why do all animo acids have L chirality? There's no reason R-chiral ones won't work. But still, *every* living thing uses the same convention.
None of these unifying factors are chemically necessary; we've proven so both with chemistry and by artificially altering bacteria to work in other ways. Yet all life shares this commonality.
You are aware than there are 40,000 species of fish, compared to 4,000 mammals (of which 1200 are bats and 1000 are rodents), right? And that fish have far, FAR more morphological, biochemical and genetic diversity than mammals, right?Originally Posted by [b
That's like saying "I'd like to buy that cheesburger, but I only have enough money for a 30-foot yacht and full-time crew." Fish are the paragons of vertebrate diversity.
Plants I'm less familair with, but suffice to say, they similarly put mammals to shame. Hell, just look at what we grow! Plants have evolved to eat animals, but no animals have evolved the ability to photosynthesize.
But if you believe God used evolution as a tool, and that speciation occurs, why do you reject the common ancestry of life?Originally Posted by [b
Just because something shares a common ancestor doesn't make it any less special. Look at your family. You all share a common ancestor, but aren't each and every one of you unique, distinct and different in your own special ways?
Similarly, why does common ancestry pose a problem to God using evolution to create life and us? Couldn't you view us like you family, all originating from the same source, yet all different, unique and special?