Not until the beginning of the 20th century did Europe's urban populations finally become self-sustaining

Not until the beginning of the 20th century did Europe's urban populations finally become self-sustaining: before then, constant immigration of healthy peasants from the countryside was necessary to make up for the constant deaths of city dwellers from crowd diseases.

J. Diamond, Guns Germs and Steel (1997), 197

It is hard to domesticate an emu, and no-one ever rode a kangaroo into battle

The zoological lottery that Jared Diamond describes - the pure chance of whether your local animals can be domesticated - enormously favoured Europe and Asia. Australia, by contrast drew a very short straw. It is hard to domesticate an emu, and no-one ever rode a kangaroo into battle. The Americas were almost as badly off, but they did have the llama. Llamas cannot compete with horses for speed, or donkeys for pack power; they also have an infuriating habit, when tired, of just stopping and refusing to move. But they are extraordinarily well adapted to high altitude; they cope well with the cold and can forage for their own food; they cab provide wool, meat and manure; and, although they cannot carry people, a healthy llama can comfortably transport about 30 kilograms of goods.

N. MacGregor, A history of the world in 100 objects (2010), 403
[73: Inca gold llama]