Artificial selection and domestication | Natural selection | AP Biology | Khan Academy

Most of us are familiar with dogs, oftentimes known as man's best friend. What's fascinating about them is that they are one species, even though different types of dogs, different breeds, could look very, very different. The fact that they're one species says that if you have a male and a female dog—any two—that in theory they could reproduce and produce viable offspring. Although, in for example, the case of this character and this character, the mechanics could get quite difficult.

But an interesting question is, where do dogs come from, and why do we have these seemingly specialized breeds amongst dogs? You might have things like a Rottweiler that's better for protection; you might have things like terriers that have been specialized to maybe go after rodents. You have things like Border Collies that are good at herding other types of animals.

The simple answer is through artificial selection and domestication. Remember, in any population of a species, there's variation in that species. When we talked about natural selection, that's where the environment might select for certain of those variants; certain of those variants might make it a little bit easier to survive or reproduce, and then those would predominate. That's how evolution happens.

Artificial selection and domestication is where humans take matters into their own hands, and instead of waiting for nature to do things, they are the selection factor. They pick which of the species get to reproduce and which ones don't. When you have that type of artificial selection, the change can happen much, much faster. Breeding is essentially artificial selection.

So dogs like this, and all the dogs we know of, had ancestors that looked like this; that looked like a wolf—that were a wolf. What we theorize is that the early stages of some wolves eventually evolving into dogs might have been more traditional natural selection, where, tens of thousands of years ago, our hunter-gatherer ancestors, as they hunted and gathered, might have left over food here and there. Some of the wolves that just happened to be the variants that were a little bit more comfortable getting close to humans might have benefited from being able to get some of that leftover food, being able to get some of that—the remains that the human beings left behind.

But then, over time, human beings probably realized that, hey, these wolves are useful to have around. Maybe they provide some form of protection. Maybe, over time, they started breeding the wolves, so the wolves that were especially friendly, the wolves that were especially good at a certain task—say protection or going after some type of an animal or retrieving things—they allowed those to reproduce together.

Over time, over tens of thousands of years, we went from wolves to dogs. Even once we had dogs, the breeding got even more specialized. As I mentioned, things like Border Collies—this was many years, many generations of breeding—where sheep herders might have selected dogs that were good at herding sheep. Terriers came from dogs that were good at going after rodents. Things like Rottweilers or dogs bred the dogs that were especially good at providing protection or defense.

And it isn't just dogs that are products of artificial selection and domestication. Pretty much any animal that you might see on, say, a farm would be the product of artificial selection and domestication. A wild pig looks like this, while the ones that you would see on a farm look like that. Once again, they would have selected for things like docility—things where they're less aggressive and they're easier to take care of.

Artificial selection and domestication do not apply just to animals. Pretty much anything you might see in the produce section of your supermarket is the product of artificial selection and domestication. There might be wild variants of these different vegetables or these different fruits. Over roughly 10 or 15 thousand years of human agriculture, every generation of crop, they would have selected for the crops that are more robust, that tasted better, that were able to grow in different climates. By allowing those variants to reproduce, we eventually ended up with the domesticated crops we see today.