Artificial selection is a term coined by Charles Darwin to describe evolution in animals that has been produced by man. As an example, the variation in dogs has been especially great. Man has produced everything from chihuahuas to St. Bernards from a few species of wild dog.
But let's look at the domestic pigeon, commonly bred in Great Britain, because that is what Darwin himself chose to specialize in.
Artificial selection allows rapid changes in a species. This is because man has one power which nature does not. Man can ensure that an animal breeds with only those animals that will preserve a beneficial trait.
To understand that, in nature an individual may possess better eyesight or stronger muscles, but it will not necessarily mate with another individual of equal caliber. as a result, many beneficial traits are likely simply lost to the species. Not so with man. Man has the ability to prevent his domesticated animals from mating with animals that he has not chosen.
These rapid changes give us the ability to see how far evolution can go in just a few thousand years.
Charles Darwin lists the type of changes that breeding has produced in pigeons:
I don't know about you, but I find these to be remarkable differences. Even the number of vertebrae and ribs differ! Sexes have begun to diverge from one another!
It's so remarkable, that it had an effect on naturalists in general, whose job it was to classify animals. That effect had a lot to do with spurring Darwin's thinking on natural selection (or evolution] …
I've mentioned before that Darwin developed his theory of evolution backwards from the way we normally suppose. We assume he worked from fossils forward, but he didn't. He developed his theory beginning with modern, living creatures and worked backwards.
It was the job of a naturalist in his day to classify organisms. If the naturalist felt that the organism and its relatives were unique enough to be an independent creation of God, then they were classified as a species. If they were so similar to a different type of organism that one seemed to have descended from the other, then they would be classified as a variety.
Darwin found it impossible to determine which was which.
And he noted that most other naturalists did, too, as evidenced by their rampant disagreement with one another on the subject.
Artificial selection confirmed the reason for the problem:
Genus is the next class above species. Not only would an ornithologist have placed these birds—known to be related by descent—in separate species, he would place them in separate genera [plural of genus].
If artificial selection can produce genus-level changes in a couple thousand years, then how much change could be produced by natural selection in hundreds of millions of years?