Diamond argues that Eurasian civilization is not so much a product of ingenuity, but of opportunity and necessity. That is, civilization is not created out of sheer will or intelligence, but is the result of a chain of developments, each made possible by certain preconditions.

In our earliest societies humans lived as hunter-gatherers. The first step towards civilization is the move from hunter-gatherer to agriculture with the domestication and farming of wild crops and animals. Agricultural production leads to food surpluses and this in turn supports sedentary societies, rapid population growth, and specialization of labor. Large societies tend to develop ruling classes and supporting bureaucracies, which leads in turn to the organization of empires.

Although agriculture arose in several parts of the world, Eurasia gained an early advantage due to the availability of suitable plant and animal species for domestication. In particular, the Middle East had by far the best collection of plants and animals suitable for domestication - barley, two varieties of wheat and three protein-rich pulses for food; flax for textiles; goats, sheep and cattle. As early Middle Eastern civilizations began to trade, they found additional useful animals in adjacent territories, most notably horses and donkeys for use in transport. In contrast, Native American farmers had to struggle to develop corn as a useful food from its probable wild ancestor, teosinte. Eurasia as a whole domesticated 13 species of large animals (over 100lb / 44kg); South America just one (counting the llama and alpaca as breeds within the same species); the rest of the world none at all. Diamond describes the small number of domesticated species (14 out of 148 "candidates") as an instance of the Anna Karenina principle: many promising species have just one of several significant difficulties that prevent domestication. For example in many parts of the world local populations have to settle for taming animals that are born wild, such as Asian elephants, because it is very difficult to breed them in captivity. Australia and the Americas also had very few large mammals as a result of an end-Pleistocene extinction, possibly because they had not co-evolved with humans and were insufficiently wary of human hunters.

Eurasia's large landmass and long east-west distance increased these advantages. Its large area provided it with more plant and animal species suitable for domestication and allowed its people to exchange both innovations and diseases. Its east-west orientation allowed breeds domesticated in one part of the continent to be used elsewhere through similarities in climate and the cycle of seasons. In contrast, Australia suffered from a lack of useful animals due to extinction; the Americas had difficulty adapting crops domesticated at one latitude for use at other latitudes (and, in North America, adapting crops from one side of the Rocky Mountains to the other); and Africa was fragmented by its extreme variations in climate from north to south: plants and animals that flourished in one area never reached other areas where they could have flourished, because they could not survive the intervening environment. Europe was the ultimate beneficiary of Eurasia's east-west orientation: in the first millenium BC the Mediterranean areas of Europe adopted the Middle East's animals, plants, and agricultural techniques; in the first millennium AD the rest of Europe followed suit.

Hence Eurasia was able to support larger, denser populations, which made trade easier and technological progress faster than in other regions. These economic and technological advantages eventually enabled Europeans to conquer the peoples of the other continents in recent centuries - using the "Guns" and "Steel" of the book's title.

Eurasia's dense populations, high level of trade, and living in close proximity to livestock also made the transmission of diseases easy, and so natural selection forced Eurasians to develop immunity to a wide range of pathogens. When Europeans made contact with America, European diseases ravaged the indigenous American population, rather than the other way around (the "trade" in diseases was a little more balanced in Africa and southern Asia: malaria and yellow fever made these regions notorious as the "white man's grave";[2]; and syphilis may have spread in the opposite direction[3]). The European diseases decimated indigenous populations so that relatively small numbers of Europeans could maintain their dominance - the "Germs" of the book's title.

Did you know the zebra, unlike the horse can't be trained to ridden.

What I like about Diamond is his debunking that certain races or cultures are smarter than others, or were held back by cultural beliefs or practices etc etc, but their progress really depended upon some pretty basic things...could grains be easily cultivated in an area? Could animals be domesticated?

And yet it's not debunked, since all of those things make up the "natural" in "natural selection." One could still argue that although Europeans or Asians aren't inherently smarter, their more favorable environment created an ecological niche that selected in favor of intelligence over, say, 100 generations. Environments like Africa, that didn't offer the same favorable environmnent for intelligence, resulted in different selection events.

I think Diamond's work is fascinating, but don't feel it's succeeded much in myth-debunking.