I think it's absolutely inarguable that the germs from the Old World devastated the New World after first contact. All at once, the New World got malaria, yell

I think it's absolutely inarguable that the germs from the Old World devastated the New World after first contact. All at once, the New World got malaria, yellow fever, smallpox, the list goes on. Meanwhile, the only disease that we think (but don't know for sure) that the Old World got from the exchange is syphillis, which can only be trasmitted sexually, and is nowhere near as devastating. I also think it's inarguable that people had domesticated more animals in the Old World. The Old World had cows, pigs, sheep, goats, chickens, cats, dogs, falcons, horses, oxen, camels, turkeys, just to name a few. The New World had dogs and llamas... and honestly I'm drawing a blank for more than that. I'm sure there were other ones, but there was nothing equivalent to horses. Whether there were more "good domesticable" animals or not is irrevelant-- we know for a fact that not as many animals were domesticated. I also disagree that domesticable animals are "key" to Diamond's theory. A larger and more dense population can just support more diseases. It's simple mathematics-- if a disease that kills its hosts can't spread before its hosts die, it dies out. It's the same reason why half a pound of uranium might go critical, but a few molecules won't. The reaction (disease) cannot sustain itself without a certain density. This is also the idea behind "herd immunity." Third, implying that the impact of a disease on a civilization wide basis has only to do with the disease itself and nothing to do with the details of the civilization itself is a casual assumption of the underlying narrative though it is blatantly false. You can use as many $10 words as you want, but I'm pretty sure wiping out 90% of the people in any civilization will have a catastrophic effect. Remember that the Black Death in Europe "only" killed 1/3 of the population.