Diamond's geohistorical approach certainly clarifies continental-scale history. Most of world history, however, is Eurasian history, and he's only sketchy on why the West Eurasians eventually overcame the East and South Eurasians.
Diamond is not content, however, to merely write the history of the last 13,000 years. He also claims that his evidence is of great political momentuousness because it shows that no ethnic group is inferior to any other: each exploited its local food resources as fully as possible. For example, after the Australian Outback explorers Burke and Wills exhausted their Eurasian-derived supplies, three times they had to throw themselves on the mercy and expertise of the local Stone Age hunter-gatherers. These Aborigines, the least technically advanced of all peoples, may not have domesticated a single Australian plant in 40,000 years, but in 200 years down under scientific whites have domesticated merely the macadamia nut. Farming only pays in Australia when using imported crops and livestock.
But, are indigenous peoples merely not inferior? In truth, on their own turf many ethnic groups appear to be somewhat genetically superior to outsiders. Diamond makes environmental differences seem so compelling that it's hard to believe that humans would not become somewhat adapted to their homelands through natural selection. And in fact, Diamond himself briefly cites several examples of genetic differences impacting history. Despite military superiority, Europeans repeatedly failed to settle equatorial West Africa, in part because they lacked the malaria resistance conferred on many natives by the sickle cell gene. Similarly, biological disadvantages stopped whites from overrunning the [high altitude] Andes. Does this make Diamond a loathsome racist? No, but it does imply that a scientific-minded observer like Diamond should not dogmatically denounce genetic explanations, since he is liable to get tarred with his own brush.
The undeniability of human biodiversity does not prove that we also differ somewhat mentally, but it's hard to imagine why the brain would differ radically from the rest of the body. Consider the fable of the grasshopper and the ant. The ant's personality traits -- foresight and caution -- fitted him to survive his region's predictably harsh winters. Yet, the grasshopper's strengths -- improvisation and spontaneity -- might furnish Darwinian superiority in a tropical land where the dangers are unpredictable.
Like many, Diamond appears to confuse the concepts of genetic superiorities (plural) and genetic supremacy (singular). The former are circumstance-specific. For example, a slim, heat-shedding Somalian-style body is inferior to a typically stocky, heat-conserving Eskimo physique in Nome, but it's superior in Mogadishu (and in Manhattan, too, if, you want to become a fashion model and marry David Bowie, like Somalian supermodel Iman). In contrast, genetic supremacy is the dangerous fantasy that one group is best at everything. Before the European explosion began in the 15th Century, it seemed apparent that no race could be supreme. Even the arrogant Chinese were periodically overrun by less-cultured barbarians. The recent European supremacy in both the arts of war and of peace was partly an optical illusion masking the usual tradeoffs in talents within Europe (e.g., Italian admirals were as inept as English cooks). Still, the rise and reign of Europe remains the biggest event in world history. Yet, the era when Europeans could plausibly claim supremacy over all other races has been dead for at least the 60 years since Hitler, of all people, allied with Japan.
The historian who trumpets the political relevance of his work must consider both the past and the future, which Diamond fails to do. Surprisingly, ethnic biodiversity is becoming more important in numerous ways. Until recently, one's location and social position at birth closely constrained one's fate. But, as equality of opportunity grows, the globalized marketplace increasingly exploits all advantages in talent, including those with genetic roots. Pro sports offer a foretaste of the future: many are resegregating themselves as ethnic groups increasingly specialize in those games they're naturally best at. In summary, Diamond may prove a better guide to the last 13,000 years than the to next 13. [More]
Diamond's first book, The Third Chimpanzee, is a much more exciting read, even though a lot of it is outdated by now. But he was a lot freer-thinking back then before he turned himself into a global monument to racial political correctness. His bank account, however, wasn't as well-padded before Guns, Germs, and Steel, though.