Diamond addresses this issue in Chapter 9 of Guns, Germs, and Steel. He cites what he calls the "Anna Karenina principle." This means that all domesticable animals share the same characteristics (docility, diet, willingness to reproduce in captivity, and so on.) In order to be domesticated, an animal must have all of these characteristics. Conversely, an animal lacking in even one of these traits can't be domesticated profitably. So a hippo, which fulfils many of these requirements, can't be domesticated purely because it has a nasty disposition. Zebras can't be domesticated for the same reason. A gazelle can't be domesticated because it panics too easily. Having established this, Diamond shows that most of the animals that are easily and profitable domesticated (the so-called Ancient Fourteen) are found in Eurasia, not in South America or Sub-saharan Africa.
Source: Diamond, Guns, Germs and Steel, 157-175.