I stand corrected, earth is 4.5 billion years old. life 3.5 or so. my statement statement refers to multi cell organisms where adaptation takes place over thousands of years. I,ll be it 200.000 to 600.000 thousands of years. I would like some clarification on artificial versus natural selection.
Ah okay I see why I was confused. 600 thousand thousand is the same as saying 600 million, but if you prefer to think in terms of multiples of thousands that's fine.
In this case I was using artificial selection to refer to selection brought about by humans, in a natural environment. I wasn't using it to refer to selective breeding, which is truly artificial selection in its most obvious form. Basically I mean that if you have an introduced organism (call it "organism A") with a given number of feral individuals, not only do they have a smaller gene pool (less variation among all individuals) than in their normal habitat, but they have absolutely no gene flow (transfer of genes between populations/communities). Additionally, the selection pressures of the new environment are different than where they originally came from (i.e. different predators, food, weather, water quality, etc...), so individuals that may be better suited for their natural environment may be worse off in their new environment. For example, at work we raise Siberian sturgeon. Siberia is a lot colder than Florida, so the individuals that can tolerate the heat do better in our environment, whereas the individuals that don't are the "least fit" and are more likely to die. This occurs even though this heat tolerance may have had no bearing on the individual in the wild.
Additionally, if organism A becomes established in a non-native environment, it can then become a selection pressure for organisms B, C, D, etc...that live in the same area. Like how cichlids in Florida compete with native fish such as sunfish. Or how birds in Florida are learning to flip plecos over to eat them and avoid their armored scales. Maybe the dumb birds are selected against!
Of course, physical adaptation takes a really long time to occur, so no human really gets to "experience" it within their lifetime. As a species we might not even have the chance to see it very often! When you think about the fact that bichirs have changed relatively little in the past 50 million years it really puts things in perspective! However, think about what we sexually select for as humans. Now we must ask: it a coincidence that humans now grow taller than they did 400 years ago? Or that men used to find heavier women attractive in the middle ages and now we find emaciation more compelling? Fat used to be a symbol of health and wealth (i.e. not lacking nutrition), but now things have changed and fat people are generally regarded as less healthy. This is shaping the way we select who gets to reproduce and pass on their genes.
