Diamond describes this concept in Chapter 9. The Anna Karenina principle says (in a rough paraphrasing of the first sentence of the Tolstoy novel) "Domesticable animals are all alike; every undomesticable animal is undomesticable in it's own way." Diamond uses this principle to explain why some animals that would have been very useful if domesticable could not be. Essentially an animal has to meet several criteria to be domesticable, or at least to be profitable to domesticate. It must mature quickly, feed on a readily available and cheap food supply, descend from a wild creature that lives in hierarchical social groups, and, essentially, not be too tempramental. If a wild animal even fails in one of these categories, it is not really domesticable (in its own way). As it turns out, most of the domesticable animals lived in Eurasia.