The animals in a given area are based upon the geographic location of that area. Most large land mammals prefer a flat, grassy, mild-tempered climate. It is areas like this where civilizations could find domesticable animals. Africa fits this description pretty well, they have crops, and they even have the greatest amount of large land mammals of any continent, but if the animals lack the traits to be domesticable then domestication is almost impossible. To classify as a useful animal for domestication, the animal would need to be at least 100 pounds, be easy to work with, have few breeding specifications, have rapid growth, and have an easy-to-control hierarchy. With more than 10 animals that fit this description, Eurasia has all but one of the domesticable animals. So, once again the people in Eurasia have fortuitously gotten the best area to live in. With the cows, horses, sheep, donkeys, goats, etc, Eurasia could have an animal till their land instead of doing it themselves. This free labor bought people more spare time, allowing more specialists to emerge, making development faster, and leaving areas without a dependable source of food even further