Eurasia ended up with the most domesticated animal species in part because it's the world's largest land mass and offered the most wild species to begin with.

Much of human history has consisted of unequal conflicts between the haves and the have-nots.

One person making a wrong decision affects the whole country.

We know from our recent history that English did not come to replace U.S. Indian languages merely because English sounded musical to Indians' ears. Instead, the replacement entailed English-speaking immigrants' killing most Indians by war, murder, and introduced diseases, and the surviving Indians' being pressured into adopting English, the new majority language.

Even to this day, no native Australian animal species and only one plant species-the macadamia nut-have proved suitable for domestication. There still are no domestic kangaroos.

All recognized famous inventors had capable predecessors and successors and made their improvements at a time when society was capable of using their product.

Measles and TB evolved from diseases of our cattle, influenza from a disease of pigs, and smallpox possibly from a disease of camels. The Americas had very few native domesticated animal species from which humans could acquire such diseases.