I was delighted by the book and used to keep it in great regard. The only problem that after one malicious person started to fact check all the premises, big part of reasoning and my faith in Jared Diamond started to crumble.
1) I suspect that everyone here heard about Irish Potato Famine. Yes, Europe was revolutionised by an American plant because it was bringing higher yields per hectare. Somehow I also was shocked that I overlooked that contradiction with whole premise of book.
Fun part: concerning crop Europeans were clearly the least lucky, as they were not only beaten by American corn/potato but also Asian rice in yield. Thus following the theory it should have doomed Europe.
By contrast, wheat comes in at about 4 million calories per acre, soy at 6 million. Rice is also very high-yielding, at 11 million, and potatoes are one of the few crops that can rival corn: They also yield about 15 million (although record corn yields are much higher than record potato yields)
Source: Washington Post
If, as LangLangC this is a comparison of modern species - US settlers were planting corn for its higher yield than wheat (Even if one moved corn to Spain in premodern times and foreign environment it had similar yields to wheat)
2) Zebras actually could be domesticated, and in XIXth century German colonisers were successfully utilising them. Yes, it has nasty character. On exactly what premise are we assuming that wild, undomesticated horses millennia ago were nice? Domestication puts very strong evolutionary pressure on animals, including making their brains smaller and their behaviour much more docile.
German colonial zebra cavalry prior to WW1
3) In North America actually spread of corn among native tribes was not showing any evidence of this claimed north-south problem. Instead it was "jumping" in weird way, showing that some other factors were dominating.
4) Modern cows origin from aurochs, which in original form were a bison size animal. According to historical accounts (extinct in XVIIth century) they were not only fearsome challenge for hunters but even people did not fully grasped that were related to cows. In other words unless in this case, against Jared Diamond claims, it was not being lucky in getting nice animal, but millennia of domestication.
There is a third kind, consisting of those animals which are called uri. These are a little below the elephant in size, and of the appearance, color, and shape of a bull. Their strength and speed are extraordinary; they spare neither man nor wild beast which they have espied. These the Germans take with much pains in pits and kill them. The young men harden themselves with this exercise, and practice themselves in this kind of hunting, and those who have slain the greatest number of them, having produced the horns in public, to serve as evidence, receive great praise. But not even when taken very young can they be rendered familiar to men and tamed. The size, shape, and appearance of their horns differ much from the horns of our oxen. These they anxiously seek after, and bind at the tips with silver, and use as cups at their most sumptuous entertainments.
Julius Ceaser desription of Auroch, from Commentaries on the Gallic War, Book 6
5) The book reasoning is based on assumption that if some specie was not domesticated, then it means it was practically impossible. In last century Russians were running a breeding experiment and managed to domesticate fox as pet as they were selecting friendlier and friendlier generations. Yes, maybe a bit pointless from practical perspective, but that's exactly the point. If one does not need some domesticated animals then does not put the effort. In consequence whoever managed the domestication of useful animals first would get and edge and manage to spread them, thus making later domestication of similar species pointless.
6) The argument concerning lack of wild horses or camels in Americas is could be equally well interpreted in the opposite direction. The problem is that both species had been driven in to extinction by early hunter-gatherers. Nothing unique. In Eurasia we managed also to more or less drive in to extinction wild horses (there are some semi-wild reintroduced like tarpan or Przewalski's horse), aurochs or wild dromaders. So equally well we may use the same data and ask whether one bothers to domesticate a specie before driving it in to extinction, and reach a conclusion that the differentiating factor was some seemingly minor decision at key divergence point.
Link to link base of research articles of the above mentioned malicious guy, who run a nasty fact check: https://thealternativehypothesis.org/index.php/2019/05/05/guns-germs-and-steel-sources/