How could wild creatures like wolves be ancestors of cute little Pomeranians? To understand, we first need to know how genetics and evolution work. Animal offspring inherit genes from their parents, and these genes indicate what traits the offspring will have. The variety of genes and the possibility of mutation allow for animal species to change, or evolve, over time. In the process of natural selection, the animals with traits that allow them to survive better will be more likely to breed, until very gradually the only members who survive end up inheriting those helpful traits.
In artificial selection, humans choose desirable traits in animals that they want to see in the animal's offspring. For example, if people want bigger horses to pull their loads, they can put the biggest male and the biggest female horses together and encourage them to breed. This increases the chances that the offspring will also be big. Using another big horse to breed with that offspring will continue the process, until finally, after generations of people continue the process on generations of horses, the entire horse species will be bigger. Using the same process, humans can breed animals to be a certain color, furrier, smaller, gentler or stronger, among other things. This is how humans domesticate animals -- so much so that wolves eventually become a different animal, gentle enough to keep in the home. Or, sheep yield more wool. Or, horses let us ride them.
If this is true, then why don't we ever see a pet panda or someone riding a zebra? It turns out that we can't domesticate every animal. Author Jared Diamond writes that humans have succeeded in truly domesticating only 14 animal species out of about 148 candidates [source: Diamond]. He proposes that for humans to domesticate an animal species, the species usually satisfies these criteria:
- The right diet: Picky eaters have always made life difficult for their mothers, so one can imagine the frustrations involved in keeping up an animal with picky tastes. Because many animals have specific dietary needs and carnivores get expensive to feed, humans can only domesticate animals that thrive on cheap, accessible food.
- Fast growth rate: The species must grow at a fast rate for herders and farmers to yield a timely return on the investment of raising it.
- Friendly disposition: Vicious animals by definition don't usually like it when humans attempt to bring them into captivity and won't let humans handle them.
- Easy breeding: If the animal refuses to breed under the conditions human captors can provide, then obviously, its period under human control is short-lived.
- Respect a social hierarchy: In the wild, if the animals form social structures in which they all follow a dominant member, then humans can establish themselves as leader-of-the-pack.
- Won't panic: Many animals freak out when they are restrained, kept in fences or perceive a threat. Cows, on the other hand, remain fairly complaisant and unflappable despite these conditions, making them easier to domesticate.
Pandas and zebras are far too violent and have thwarted human attempts to domesticate them. However, exceptions might come to mind after examining Diamond's list. For instance, isn't the wolf (as predecessor to the dog) vicious and the cat solitary? The stories of dogs and cats are unique ones that we'll learn about a little later.
On the next page, we'll take a look at the long story behind domestication.