Gregory Cochran revisits Guns, Germs, and Steel

Sunday, September 10th, 2017

Gregory Cochran can be an extremely uncharitable critic, but the middle of his review of Jared Diamond’s Guns, Germs, and Steel is measured:

Most significant domestic animals were domesticated somewhere in Eurasia or North Africa, only a couple in South America (llamas and vicuna), nothing in the rest of the world. Diamond argues that this wasn’t because populations varied in their interest in or aptitude for domestication. Instead, the explanation is that only a few large animals were suitable for domestication.

He’s unconvincing. Sure, there were places where this was true: what were the Maori in New Zealand going to domesticate — weta? And Australia didn’t have a lot of large mammals, at least not after people wiped out its megafauna. But there are plenty of large animals in Sub-Saharan Africa, yet none were domesticated. He argues that zebras were wilder, more untameable than horses — but people have tamed zebras, while the wild ancestors of horses (tarpans, which survived into the 19th century) were usually described as untameable. The wild ancestors of cows (aurochsen, which survived into the 17th century) were big and mean. They enjoyed impaling people on their horns and flinging them for distance. The eland is a large African antelope, and by Diamond’s argument it must be untameable, since the locals never tamed it. But in fact it’s rather easy to tame, and there’s now a domesticated version.

The key here is that one can select for disposition, for tameness, as well as obvious physical features, and an animal can go from totally wild to cuddly in ten generations — remember the selection experiment with Siberian foxes. In the long run disposition is not a big obstacle. Selection fixes it — selection applied to above-neck traits.

Diamond makes a similar argument about domesticating plants as crops: only a few plants were suitable for domestication, and part of the reason that some populations never developed crops was a lack of suitable plant species. I’ll give him Eskimos. but that’s about it.

Here his argument is far weaker: there are a buttload of plants that could be domesticated and might be quite useful, yet have not been. Enthusiastic agronomists keep trying to get funding for domestication of jojoba, or buffalo gourd, or guayule — usually government interest runs out well before success.

The reason that a few crops account for the great preponderance of modern agriculture is that a bird in the hand — an already-domesticated, already-optimized crop — feeds your family/makes money right now, while a potentially useful yet undomesticated crop doesn’t. One successful domestication tends to inhibit others that could flourish in the same niche. Several crops were domesticated in the eastern United States, but with the advent of maize and beans (from Mesoamerica) most were abandoned. Maybe if those Amerindians had continued to selectively breed sumpweed for a few thousand years, it could have been a contender: but nobody is quite that stubborn.

Teosinte was an unpromising weed: it’s hard to see why anyone bothered to try to domesticate it, and it took a long time to turn it into something like modern maize. If someone had brought wheat to Mexico six thousand years ago, likely the locals would have dropped maize like a hot potato. But maize ultimately had advantages: it’s a C4 plant, while wheat is C3: maize yields can be much higher.

Why didn’t people domesticate foxes, back in the day? Is it because foxes are solitary hunters, don’t have the right pack structure and thus can’t be domesticated, blah blah blah? No: they’re easy to domesticate. But we already had dogs: what was the point? You had to be crazy like a Russian.

One other factor has tended to suppress locally-domesticated plants — what you might call alien advantage. If you grow a crop near its origin, there will be local pests and pathogens that are adapted to it. It you try growing it in a distant land with a compatible climate, it often does very much better than in its own country. So… crops from Central and South America have done very well in Africa, or sometimes in Southeast Asia. Rubber tree plantations work fine in Malaysia and Liberia but fail in Brazil. Maize is the biggest crop in Africa, while manioc and peanuts are important. Most cocoa is grown in Africa: most coffee is grown in South America.

Sometimes, Diamond was wrong, but in a perfectly reasonable way, not in the devoted service of a flawed thesis, but just because the facts weren’t all in yet. We all need to worry about that.

He considered the disastrous impact of Eurasian and African diseases on the inhabitants of the New World, contrasted with a much smaller impact in the opposite direction, and concluded that a major factor had probably been transmission from domesticated animals. Eurasians domesticated quite a few animals, Amerindians not many — perhaps that was the explanation. In Guns, Germs, and Steel (p 207), he mentions measles, tuberculosis, smallpox, influenza, pertussis (whooping cough), and falciparum malaria as likely cases of transmission from domesticated animals.

We know a lot more about this we did twenty years ago, since we’ve been sequencing the genes of everything in sight — and it appears that Diamond was mistaken about the most important members of that list. TB appears to be ancient in humans, smallpox probably came from some East African rodent, while falciparum malaria seems to have derived from a form of malaria carried by gorillas. Measles really does descend from rinderpest, a cattle plague, but then rinderpest (and mumps) probably descend from bat viruses. Domesticated animals do play a role in influenza, along with wild birds. I don’t think we know the origins of pertussis.

So why then was the Old World such a fount of infectious disease? Well, it’s bigger. Civilization was older, had had more time to pick up crowd diseases. Humans have close relatives in the Old World that carried important pathogens (chimps and gorillas), while Sasquatches are germ-free. Important pathogens, especially those with insect vectors like malaria, maybe couldn’t make it to the New World through ice-age Beringia. Transportation and trade were more advanced in the Old World, and spread disease more efficiently.

I don’t think that Diamond was making excuses for Amerindians in this, as he was when talking about domestication: having lots of plagues isn’t usually considered an accomplishment. Origination in livestock seemed like a reasonable idea at the time, considering the state of the art. It seemed so to others as well, like William McNeill. It’s not totally wrong — definitely true for measles — but it’s not a huge part of the explanation.

Sometimes Diamond was right. He says that it’s a lot easier for crops to spread east and west than north and south, and he’s correct. Middle Eastern crops worked in much of Europe, especially southern Europe, and also were important in India and China. On the other hand maize had to adapt to shorter growing seasons as it spread into North America: this took time. Post-Columbian spread of maize in Africa was much faster.

Geographical barriers were major factors in slowing the spread of civilization. Although a few distressed mariners must have occasionally crossed the Pacific in ancient times, nothing significant (in terms of crops or ideas) seems to have made it across before Columbus. Amerindians had to develop everything themselves, while populations in the Old World were sharing seeds and ideas (and plagues). Having to invent everything from scratch is a disadvantage, no question.

The geography of the Americas greatly inhibited contact between Mesoamerica and the Andean civilization: even today the Pan-American highway doesn’t go all the way through. The Sahara was even worse, but most of the budding civilizations of Eurasia did manage some contact.


  1. Adar says:

    Think rather wine, olive oil and cheese. The ability to take a perishable [grapes, olives, milk] product and process for long-term use was a big-step forward at least for the western world and at many levels.

  2. T. Greer says:

    He is being argumentative for the sake of it. The fox/dog example is enough to show he is out of his depth.

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