Guns, Germs, and Steel

This chapter focuses on how certain wild plants got turned into crops—especially those crops whose ancestors were deadly or look dramatically different to their successors.

Plant domestication involves growing a plant and causing it to change genetically from its wild ancestor. The first farmers could not have anticipated the results of their actions, so how did they, for instance, turn poisonous almonds into a safe food source without prior knowledge or conscious effort?

Like all living things, plants must spread their offspring to areas in which they can flourish and pass on their parents’ genes. To do this, many plants trick animals into carrying their seeds. Similarly, in the early, accidental stages of crop evolution, wild plants evolved in a way that encouraged humans to eat and disperse their fruit. Humans may have expelled seeds in the same manner as animals, but they may also have spilled plants that they have collected along the route home. Diamond refers to such sites as “the first agricultural research laboratories” (117).

When the first farmers started to sow seeds intentionally, they would choose the same plants for the same criteria that they had chosen to gather. One obvious criterion is size. For example, in the beginnings of agriculture, humans selected and cultivated the most appealing large peas. Over time, this led to an increase in the average size of a pea.

Diamond proposes a theory for how almonds ever reached the first stage of domestication. Their wild ancestors possessed a bitter chemical and were liable to kill, but a mutation that occasionally emerges in individual almond trees that prevents them from synthesizing this bitter chemical. These trees die out in the wild because birds eat their seeds, but the children of early farmers may have also sampled and collected these seeds. These “mutated” seeds would have therefore been planted by ancient farmers.

In addition to size and tastiness, fleshliness, long fibers, oily seeds, or seedlessness are other factors that could prompt people in their selection of wild plants. Seedlessness, in particular, is notable in that it goes against the original evolved function of wild fruit (which was to disperse its seeds). Human selection can therefore alter the evolution process and its function.  

Early farmers brought other types of change unwittingly. Farmers chose which crops to domesticate based on both visible and invisible characteristics, with the latter including seed dispersal mechanisms, germination inhibition, and reproductive biology. This meant that plants could be selected for different and sometimes even opposing qualities: Whereas farmers chose plants with larger seeds in some cases, there are other instances in which they chose plants with smaller seeds. A single plant species could even be variously selected for different purposes, meaning that crops were not uniform in appearance.

Wild plants turned into crops because of farmers’ selection. However, plants were also subject to natural selection, and this often related to the environment.

Overall, then, the selection of wild plants could involve conscious and/or unconscious criteria, but the ensuing transformation of these plants into crops began as an unconscious process. It involved selecting from the available wild plants, with the chosen plants then competing against one another in their new environment—an environment in which those plants that thrived in the wild were likely to find themselves at a disadvantage.

Why didn’t agriculture develop in some suitable areas? And, where it arose independently, why did it do so much earlier in some areas than in others? Diamond subsequently suggests two possible explanations: There were either problems with the local people or problems with the available plants.

It is easy to assume that an area with a suitable climate must be home to plenty of wild species that could be domesticated. However, the vast majority of such plants would be inedible or would provide insufficient nutrition. Nevertheless, the failure to domesticate wild plants can sometimes be puzzling. 

To address this issue, Diamond considers three geographic areas: the Fertile Crescent, New Guinea, and the eastern United States. The Fertile Crescent was perhaps the earliest center of food production, while the latter two regions domesticated crops but with much less success.

The Fertile Crescent had advantages over the other two areas. It had a “Mediterranean climate” that proved beneficial for its plant life. The ancestors of many Fertile Crescent crops were abundant and productive, requiring few additional changes when they were cultivated. The Fertile Crescent was home to many plants that usually pollinate themselves, and only occasionally cross-pollinate, avoid unhelpful cross-breeding. The region also possessed an especially high diversity of plant and animal life along with the greatest climatic variation and a wide range of altitudes and topographies, fostering staggered harvest seasons that aided hunter-gatherers by letting them harvest seeds progressively. The region also possessed a wealth of large mammals, with the goat, sheep, and cow having been domesticated very early, so inhabitants could “quickly assemble a potent and balanced biological package for intensive food production” (141-142). Lastly, sedentary villages based on cereals already existed prior to the rise of food production in this area. Hunter-gatherers may have therefore been predisposed to agriculture and herding.

Was the comparative lack of success of New Guinea and the eastern United States the fault of the people inhabiting these areas? Were prospective farmers well acquainted with the local plant species or did they overlook ancestors of valuable crops? Also, if they did have sufficient knowledge, did they exploit it or were there cultural factors that prevented them from doing so?

Studies carried out by ethno-biologists on the lives of hunter-gatherer peoples and farming peoples who still depend to a large extent on wild food indicate that such peoples “are walking encyclopedias of natural history” (143)—it is only when people become increasingly dependent on domesticated plants and animals that such knowledge becomes lost. In short, it seems unlikely that the first farmers would have overlooked species that were of potential value. Evidence also indicates that they put this knowledge to good effect by selecting the most useful plants from those available.

Diamond concludes that, in both New Guinea and the eastern United States, food production was limited by the raw materials available and required imports in order to succeed, not by a lack of knowledge on the part of these regions’ inhabitants. Areas in which food production never developed independently “may have offered even less in the way of wild plants and animals suitable for domestication” (153).

Diamond warns against exaggerating two points: people’s readiness to accept better crops and livestock, and the constraints that local plants and animals imposed. There are numerous examples of societies rejecting innovations that would have been productive—there are always societies that will resist change. Societies that refuse innovation are more likely to be displaced or conquered. 

In regions where people failed to domesticate animals, available wild animals presented similar problems as plants in regions that didn’t develop food production.

Diamond defines animal domestication. A domesticated animal has been bred in captivity and is different to its wild ancestors on account of two processes: the human selection of animals most useful for human purposes and the automatic evolutionary responses of animals to these modified forces of natural selection.

Domesticated animals have diverged from their wild ancestors in various ways: size, greater retention of wool, higher milk yields, smaller brains, and less developed sense organs. In one example, wolves differ greatly from the many breeds of dogs that constitute their domesticated descendants.

There are 14 species of large herbivorous domestic animals, and the ancestors of 13 of these animals were limited to Eurasia, the world’s largest and most ecologically diverse landmass. It remains surprising, though, that some of the animals in other regions were not domesticated. Why were Eurasia’s horses domesticated while Africa’s zebras were not?

Diamond argues that some species were simply too difficult to domesticate. The first issue is diet, as some species’ food requirements or preferences mean that domestication is not worth the effort. The second is growth rate—an animal needs to reach adult size quickly in order to warrant domestication. Captive breeding can also be problematic, in that some species—such as cheetahs—refuse to mate in captivity. Other species, meanwhile, fail because of their ferocious disposition or a tendency to panic. Lastly, social structure can constitute a major obstacle—animals that already live in herds adapt to domestication and herding better than animals used to a solitary lifestyle or exclusive territory.

Overall, then, domestication can be unviable for various reasons. Eurasia was home to viable animals for three reasons: the greater number of candidates in that region as a result of its large area and diverse ecology, the extinction of potentially viable animals during earlier eras, and a higher percentage of surviving animals being suited to Eurasia than other regions.

Referring to a map of the world, Diamond points out that the major axis of the Americas and Africa is north-south whereas the major axis of Eurasia is east-west. This has had an impact on the rate at which crops and livestock—and possibly writing, wheels, and other inventions—have spread.

The spread of food production is highly relevant to understanding geographical differences. Food production developed independently in no more than nine regions, yet it spread to and became established in many other areas. However, the spread of food production was not uniform.

Charting the different trajectories of crop domestication, Diamond concludes that food production spread out of Southwest Asia more readily than out of the Americas and Africa.

For the most part, food production throughout western Eurasia consisted of Fertile Crescent domesticates, which preempted other attempts to domesticate the same wild ancestors; once the crop was made available; there was no longer any need to gather it from the wild.

The reason why is the central point of this chapter: Eurasia’s east-west axis is conducive to the spread of resources, as points distributed along the same latitude share the same day length and seasonal variations. Animals are likewise adapted to the latitude-related features of climate; domesticates originating in the Fertile Crescent are well suited to the regions into which they proceeded to spread.

The diffusion of resources from the Fertile Crescent along Africa’s north-south axis was a more fraught process, with both animals and crops hampered by disease and unfamiliar climates. Only when European settlers brought the Fertile Crescent crop package that agriculture could thrive in this zone. The Americas’ north-south axis presented similar problems. For instance, the cool highlands of Mexico would have constituted ideal conditions for various resources from the Andes, yet the northward spread of these resources was halted by the hot lowlands of Central America. Examining Native American crops also reveals the legacies of numerous independent domestications, reaffirming the slow spread of crops along the north-south axis.

Of course, latitude is not the only relevant consideration and, as Diamond makes clear, locations along the same latitude do not always have the same climate. For instance, crop diffusion along the axis between Southeast and Southwest America progressed slowly due to the aridity of the intervening area.