FWIW, I've been going over in my mind whether Lenski's experiment (which CLEARLY demonstrates evolution via adaptation), reflects "natural selection" or "artificial selection". I'm leaning more towards "natural selection" now, although that term implies changes that occur without influence of humans, but due to nature; in the experiment, scientists are obviously playing the role of God....
However, the team didn't actually select for those bacteria that could metabolize citrate, since that finding caught them off-guard (it was added as a culture media), so it's not an adaptation that arose via artificial selection.
The key is the term "selection": who's doing the selecting? If it's a result of changes in the environment, even those changes controlled or even caused by scientists, it's an adaptation that falls under the category of "natural selection".
http://wiki.answers.com/Q/What_is_the_difference_between_natural_and_artificial_selection
Natural selection is the result of natural factors, which favour certain variations. Artificial selection is the deliberate selection of certain traits (by humans), for example a Poodle is the result of artificial selection.
Natural selection occurs when a particular feature gives an organism a survival or mating advantage-- so for example, giraffes with longer necks were better able to feed themselves than those with shorter necks. Over time longer necked giraffes were better able to survive and breed. So longer necks were selected for naturallly.
Artificial selection is when humankind chooses certain traits and breeds organisms for that trait. Example-- the domestic dog. The original organism was the wolf. Humans chose certain traits, such as size or temprement and bred together those with the desired trait(s). Hence the various breeds we have today.
Natural selection is largely determined by environmental factors, where nature chooses organisms with the best traits for survival.
- Tigers developed stripes so they could sneak up on their prey easier. The stripy tigers caught more prey, became healthier than tigers that have more trouble catching prey, and produced more stripy offspring.
- For example, long-necked giraffes are chosen by nature because they're tall and can reach higher leaves, while shorter-necked giraffes can't reach as high and might starve to death.
Artificial selection is controlled by humans, where a person chooses which traits of the organism that he wants it to have.
- Pug dogs have pug faces because people bred male dogs with pug-ish faces and female dogs with pug-ish faces to produce offspring with totally pug faces.
- People choose the fat cows to breed more fat cows because they've more meat. This decreases the eventual number of skinnier cows.