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Farmers Rout Hunter-Gatherers
Diamond Posits a Plausible Human Past

By Rich McManus

On the Front Page...

Those of you already comfortable giving 50-minute extemporaneous speeches based on your Pulitzer Prize-winning book may not have been impressed, but the audience that heard Dr. Jared Diamond tour 13,000 years of human history at the NIH Director's Cultural Lecture Sept. 18 in Masur Auditorium rewarded him with sustained applause that didn't so much acknowledge the feat of organization and memory as honor an intellectual adventurer who didn't let disciplinary boundaries impede a far-ranging and compelling mind.


Dr. Jared Diamond

Ironically, it was a boundary that Diamond first referred the crowd to following his introduction by NIH acting director Dr. Ruth Kirschstein. She had forewarned that Diamond was about to compress 13,000 years into an hour's talk — "an achievement in and of itself" — but had lingered on Diamond's more extraordinary ventures, including 19 arduous expeditions to islands in the southwest Pacific, and his recent acceptance of the National Medal of Science honor from President Clinton. But when Diamond took the stage, he insisted, "I really am a biomedical researcher hired by UCLA to do biomedical research, and I thank the NIH for its generous support of my work since 1965. My history work," he quipped, "was bootlegged on the side."

It's true — Diamond is a professor in the department of physiology at the UCLA School of Medicine — but it is his extracurricular work, including Guns, Germs and Steel: The Fates of Human Societies, a 1998 book that won the Pulitzer Prize, that has earned him wider acclaim. "The British edition of my book had the subtitle, 'A Short History of Everybody for the Last 13,000 Years,' but it was disallowed by my American publisher," he confided.

He began by observing that virtually everyone in the packed hall was of Old World-Eurasian origin. "But if we had held this lecture 500 years ago, all of you would be Native Americans. Why didn't it turn out the opposite way?"

The short answer is that cultures blessed by environments favoring agriculture had distinct advantages over nomadic hunter-gatherer cultures; farmers are more stable, numerous, technologically advanced, and developed herd immunity to infectious diseases that were imparted, ironically, by their proximity to domesticated animals. Hunter-gatherer cultures such as inhabited North America 500 years ago succumbed eventually to diseases imported from abroad: "95 percent of the Native American population was killed by European infectious diseases," Diamond reported.

Like a man assembling an enormous jigsaw puzzle, Diamond logically resolved a variety of asymmetries. Whereas slides of faces from around the world displayed the great heterogeneity of the globe's genetic makeup, Diamond discovered large areas of both diversity (the Indian subcontinent, with 1,000 languages, also Australia and sub-Saharan Africa — "the most diverse of all") and vast homogeneity (Europeans, tropical southeast Asia, where "from Malaysia out to the Easter Islands, the people are very similar to one another.") Why, he asked, are there such areas of homo- and heterogeneity?

The time factor — how long humans have inhabited various places — fails to account for these patterns. But what does impose order on seeming chaos is agricultural expansion in the past 13,000 years, arising from some nine "heartlands" or "homelands" founded on farming.

"Prior to agriculture, everybody was involved in hunting and gathering," Diamond explained. The nomadic lifestyle was characterized by low population density; "There were about four years between kids, which corresponds to the age at which children can start walking with their nomad parents." These societies didn't produce storable food surpluses: "The printing press, the iron forge, tools and parts — you didn't need these if you were picking up and moving every two weeks."

Diamond (c) accepts a plaque commemorating his NIH Director's Cultural Lecture from Dr. Ruth Kirschstein, acting NIH director, and Dr. Michael Gottesman, NIH deputy director for intramural research.

The rise of agriculture, on the other hand, led to sedentary societies, "living next to orchards, gardens and pastures." A population explosion accompanied the emergence of farming: "There were two years or fewer between births, rather than four...If you're not shifting camp, you can develop heavy technology. You can store food to support the folks who won't devote any time to growing food — the artisans, the kings, chiefs, members of Congress, and other social parasites," he observed. The much larger populations sustainable by agriculture — Diamond said the ratio was about 1,000 farmers per hunter-gatherer — enabled farmers "to kill or drive out hunter-gatherers in all areas suitable for farming." The larger farm societies also evolved germs to infect others. "There were enormous competitive advantages conferred by agriculture, allowing farming societies to smoosh or compete with neighbors," he said.

Turning to the world's flora and fauna, Diamond noted "there are so few plants and animals that can be usefully domesticated." For example, there are about 4,000 species of wild mammals, two-thirds of which are rats or bats, "which you can't milk or hitch to a cart." Of some 148 candidate species, only 14 were eventually domesticated, he said, "and 13 of them are Eurasian species, including cows, sheep, goats, pigs, horses, camels, donkeys, yaks and water buffaloes.

"Mammals need a suite of characteristics — at least six," he continued. "You must be able to feed them easily (the koala bear eats the leaves of only one type of eucalyptus tree, hence is unsuitable for domestication), they must reach maturity in a reasonable amount of time (gorillas don't reach full size for 15-20 years, which would exhaust a farmer's patience and resources), they shouldn't fight back ("The grizzly bear would be good for food — it reaches full size in only five years, but it has a nasty disposition, and the power to back it up"), they should breed easily (some animals refuse to breed in captivity, including the vicuna, "producer of the world's finest wool"), they should have a follow-the-leader social structure (sheep being the ideal; North American bighorn sheep, however, have no such structure and can't be herded) and they should not be able to leap or break fences (gazelles tend to panic when penned).

Interestingly, the asymmetry of disease distribution around the world mimics the asymmetry in the distribution of mammals, Diamond discovered. "The exchange of diseases has been almost entirely in one direction" — from agri-based cultures to hunters. "Crowd epidemic infectious diseases such as smallpox and measles need large populations to sustain themselves, moving from subgroup to subgroup in time for a new crop of babies to emerge...Diseases like smallpox can't have been with us for more than 10,000 years."

Diamond maintains that herd domestic animals are the origin of most human pathogens, passed as zoonoses, and eventually becoming specialized diseases of humans. "Measles came from cattle, so did tuberculosis," he said. "Influenza is from pigs, pertussis is from pigs." He is still hunting for the animal origins of smallpox, mumps and rubella, and challenged NIH scientists to help him in the quest.

As for plants, of 200,000 wild plant species, only a few are suited for domestication. Cereals, he said, provide half of humanity's calories today, but only 56 species of large-seeded wild cereals are edible; these tended to originate from the eastern Mediterranean and Fertile Crescent, along with China, about 8,500 B.C. That 90 percent of the languages spoken by modern humans trace their origins to these two homelands is no surprise to Diamond.

The asymmetrical spread of crops and livestock around the globe can be explained, at least in part, by considering a simple geographic fact: Eurasia, with its 10,000-mile east-west axis, offers a largely continuous habitat, whereas, Africa and the Americas, with their longer north-south axes, in which day length and climate vary greatly, offer diverse habitats. "That's why the wheel never made it from Mexico to the Andes," said Diamond, by way of illustration.

"The first farmers had huge advantages — politically, agriculturally, technologically — over hunter-gatherers, whom they conquered and infected," Diamond summarized. "The ancient equivalents of guns, germs and steel led to massive population turnovers...Environment, not human biology, is the answer to the supremacies we see today.

"The broadest pattern of history is attributable to differences among continental environments, not biological differences among the people themselves," he concluded.

During a brief question period, Diamond was asked to look 13,000 years into the future and make predictions. "The coming 50 years from now will be the subject of my next book," he teased, but warned that a flood of environmental problems will preoccupy humanity in that timeframe. "Let's get past them first," he counseled.

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