While I’m away, here’s a post in the spirit of the “basic concepts in science” thingee that’s been floating around ScienceBlogs.
I received an email about a recent post that asked why pesticide resistance in insects isn’t an instance of artificial selection as opposed to natural selection. The difference between artificial selection and natural selection isn’t that the selective agent (e.g., pesticides) is a result of human activity. The difference is in what determines what is the ‘fittest’: a person’s decision as to what traits are preferable, or differential survival and reproduction. Artificial selection occurs when organisms with a certain trait or traits, such as looking like a Pomeranian, are chosen and allowed to survive and to reproduce. The ‘fitness criterion’ involved isn’t survival and reproduction: it’s the judgement of the human running the experiment that defines what is the most fit (I don’t think Pomeranians in the wild would be very fit, but rather, a yummy snack for some nasty carnivore).
In the case of pesticide resistance, farmers who use pesticides aren’t intentionally breeding those individuals that happen to be resistant to the pesticide (in fact, they’re trying to kill all of the pests). While the selective pressure, pesticides, is of human-origin, which insects survive and reproduce is not based on an artificial criterion (e.g., I like bugs with red wings), so this is natural selection.