[Arthalion]

What about the camel, elephant, water buffalo, yak, llama, and alpaca?

There's a difference between domestication and taming. The use of the animals you mention are all still heavily dependent on wild stock to supplement domestic breeding. With domesticated animals, you have a closed system leading to adaptations specifically for human use. With tamed animals, you still have an animal identical to its wild counterpart, but which is simply living under the control of man.

Pigs, sheep, and dogs are domesticated. Elephant and yak are tamed.

[Jack Black]

Good insight. Because there are tame zebras in the circus.

I'm not an expert but I believe that camels meet your definition of domesticated. (I don't think there are significant wild herds, and racing camels have been bread for hundreds of years (or more).

I don't know much about water buffalo or llamas and alpacas.

Yak wander around in herds on the Tibetan plateau?

[wyattearp]

Pigs, sheep, and dogs are domesticated. Elephant and yak are tamed.

We raised hogs when I was a kid. If you think they are domesticated, toss them some meat sometime. It'll scare the cr*p out of you. I had to be very, very careful in the field with them (four acres is a bit big to call a "pen"). If they thought they had the upper hand...