Before I begin this unfavorable review of Jared Diamond's so, so long new book, The World Until Yesterday: What Can We Learn from Traditional Societies?, I want the reader to know exactly how I will use the troublesome word "theory." Now, in science, a theory is a hypothesis that has been supported by a lot of experimental evidence, and a hypothesis is basically a good guess that needs to be tested. In philosophy, a theory is more like a hypothesis than a scientific theory; it's a guess or concept that directs a course of thinking and, when brilliant, has great explanatory powers. Karl Marx's Das Kapital, for example, has a theory that explains how capitalism works: It exploits a peculiar attribute of the commodity called labor—peculiar because it's the one commodity that can generate a surplus. (This theory proved to be brilliant because it explained and unified a large number of the seemingly disparate social, cultural, and economic phenomena in societies dominated by the logic of self-interested wealth accumulation.) In the present review, I will use this sense, the philosophical sense, of theory.

Jared Diamond is many things: a biologist, a physiologist, an evolutionary psychologist, a geographer, and an ornithologist who once worked with the great evolutionary biologist Ernst Mayr and published academic papers about my favorite feathered creature, the bowerbird. Guns, Germs, and Steel is the book that made Diamond famous, but his best book is his first, The Third Chimpanzee, which is short and presents something of a map for this trilogy: Why Is Sex Fun? (his second book), Guns (third), and Collapse (fourth). Diamond's latest book, The World Until Yesterday, lacks what we find in the first four: a theory.

Guns, for example, opens with a New Guinean asking the author this memorable question: "Why is it that you white people developed so much cargo and brought it to New Guinea, but we black people had little cargo of our own?" Meaning, why do Westerners have more inventions, tools, equipment, products, and devices than Melanesians. Both are the same animal—humans—and both have the same intellectual and linguistic capacities. And yet, one has much more stuff—cargo—than the other. Diamond answered this difficult question with a bold theory: It has to do with the shape or orientation of the continents. Europe and Asia have a horizontal orientation of axes, whereas South America and Africa are vertical. The consequence of a horizontal axis is a more or less uniform climate, and this made East/West exchanges of ideas, innovations, inventions, animals, and crops relatively easy. North/South exchanges, on the other hand, were slowed or entirely blocked by the variety of climates (desert, rainforest, savanna) that characterize a vertical continent. This theory rewarded the reader with lots of interesting and even surprising explanations.

The World Until Yesterday opens with a scene at an airport—there are screeners for x-raying luggage, conveyor belts, check-in counters, computers, ATMs, people talking on cellphones, pilots walking with flight attendants, police officers, and so on. This could be any airport in Europe or the United States, but it's in Papua New Guinea, and the pilots, flight attendants, law officers, and counter clerks are the grandchildren or even children of people whose leading technologies had not advanced beyond stones, bows, and arrows. Diamond then compares the scene at the modern airport with the photographs taken of New Guinea's Highlanders in 1931: "In those photographs, the Highlanders who had been living for millennia in relative isolation with limited knowledge of an outside world, stare in horror at their first sight of the Europeans."

The question Diamond seems to be on the verge of asking sounds similar to the one at the opening of Guns: How is it possible that, within a generation or two, a society can go from grass skirts to mastering information technologies and air transportation? But Diamond doesn't ask this question, which, in any case, doesn't require a grand theory to answer: New Guineans are humans, and the Western technologies to which they have quickly adopted were designed by and for humans. Diamond asks instead: Are there things that we hypercivilized humans can learn from our vanishing primitive past? If so, what are they? His book then goes on and on about the good and bad things, pluses and minuses of this and that traditional way of life. None of the information is new, and much of it is pushed by every evolutionary psychologist you've ever heard of. Diamond even spends a lot of energy explaining a fact that evolutionary psychology loves to no end: Statistically speaking, primitive people are more violent than civilized people.

Because the book has no theory, it has no real direction or momentum or new insights. Seriously, Diamond wrote almost 500 pages to tell us Westerners to stop eating fried chicken! recommended