Threshold 7—Agriculture

Threshold 7—Agriculture

Lecture 24

Humans transformed the environments of entire continents by systematically ring the land.

Threshold 7 of this course introduces a new type of technology: agriculture. The appearance of agriculture set human history off in entirely new directions by increasing human control of food, energy, and other resources. Rather as gravity pulled together clouds of hydrogen and helium atoms to form the rst stars, so agriculture generated denser and denser human communities until, eventually, entirely new forms of complexity began to emerge, including cities, states, and entire civilizations. This lecture describes the appearance of agricultural societies, de nes agriculture, and discusses agriculture’s impact on human history.

The “early Agrarian era” is the rst of two subdivisions of the Agrarian era of human history. It began with the appearance of agriculture, slightly more than 10,000 years ago, and ended with the appearance of the rst cities, about 5,000 years ago. That marks the beginning of the second subdivision of the Agrarian era, which we will call the “later Agrarian era.” The early Agrarian era was the rst era of human history in which there were communities that supported themselves mainly from agriculture.

Seen globally, the early Agrarian era lasted from the appearance of agriculture, more than 10,000 years ago, until the appearance of the rst Agrarian civilizations, just over 5,000 years ago. However, in many parts of the world agriculture appeared later, and so did Agrarian civilizations, so dates for the era vary signi cantly in different regions. To understand global changes during this era, it will help to think of the world as divided into four major “world zones,” whose histories were so different that they might as well have taken place on different planets. These were Afro-Eurasia (Eurasia and Africa), the Americas, Australasia (including Papua New Guinea), and the Paci c.

Agriculture evolved independently in at least six separate parts of the world, scattered throughout the three oldest world zones, within just a few thousand years. (Note that the dates I will give are approximate, and new evidence could modify them in the future. They are mostly based on radiometric dating techniques, which are generally given as dates “BP,” or “before present.” Strictly speaking, “the present” means about 1950 C.E., the date when radiometric techniques rst began to be widely used, but for our purposes we can ignore this minor difference.)

The earliest evidence of agriculture comes from the Fertile Crescent, between modern Turkey, Iran, and Egypt. Here, agricultural villages appeared as early as 11,000 BP. Their main domesticates were wheat, barley, peas, and lentils; sheep, goat, pig, and cattle. Agriculture based more on animal domesticates may also have appeared in parts of the Sahara, which was then wetter than today. Between 9,000 and 6,000 years ago, agriculture based on taro, sugar cane, and banana appeared in the highlands of Papua New Guinea, in the Australasian zone. By 9,000 BP, agriculture based on rice, millet, pigs, and poultry had appeared in China. By 9,000 BP, agriculture was well-established along the Indus River in modern Pakistan, perhaps as a result of Mesopotamian in uence. From Pakistan, it spread to much of the Indian subcontinent. By 5,000 to 4,000 BP, agriculture based on millet, yams, African rice, and cattle had appeared in sub-Saharan Africa, though it may have appeared earlier in the Sahara and Sudan.

By 5,000 to 4,000 BP, agriculture based on maize, beans, squashes, manioc, tubers such as potatoes, and small animals such as guinea pigs was present in Central Mexico and the Andes, in the American world zone. By 4,000 to 3,000 BP, agriculture based on squashes and local crops such as sumpweed may have appeared independently in the eastern parts of today’s U.S.

What is agriculture? De ning agriculture turns out to be tricky. From a biologist’s point of view, agriculture is an intense form of “symbiosis,” or cooperation between different species. “Mutualism” is a type of symbiosis involving relations between species that seem to bene t both species. For example, honeypot ants keep herds of aphids. They protect them, help them reproduce, and extract “honeydew” by stroking them with their antennae. Other examples include the relationship between owering plants and

pollinators such as bees and birds. Symbiotic relationships can become so close that the species start to “coevolve”: If one changes the other has to change, too, because neither can survive any longer on its own.

So here’s a preliminary de nition of agriculture: Agriculture is a symbiotic relationship between humans and the species we call “domesticates.” Domesticates bene t because they receive protection from humans, which is why their populations are so large. Many domesticates could no longer survive without human help. Maize cannot seed itself, and domestic sheep are helpless against predators. Humans bene t because they receive food and other services from their domesticates. If maize or sheep were to vanish overnight, millions of humans would die of starvation.

We and our domesticates coevolve, but in distinctive ways. Domesticates have mostly changed genetically. Domestic cattle, for example, are smaller and more tractable than their wild ancestor, the fearsome aurochs. Humans have mostly changed culturally. Farmers are genetically more or less identical to their Paleolithic ancestors but have very different lifeways. However, even humans have undergone some genetic changes. For example, genes allowing adults to digest raw milk are common among livestock herders. In summary, agriculture is a symbiotic relationship in which humans help favored species reproduce in return for food and other services.

Agriculture transformed human history by increasing human control of energy and resources. How? Agriculturalists clear away species they cannot use (“weeds” or “pests”) in order to increase production of those they can use (domesticates). These activities usually reduce total biological productivity but channel more of the Sun’s energy, captured through photosynthesis, toward species that humans can use. The result is an increase in our species’ share of biospheric resources. In other words, agriculture counts as a successful grab for a larger share of the biosphere’s resources by a single species, our own.

Agriculture is a symbiotic relationship in which humans help favored species reproduce in return for food and other services.

Another way of putting this is to say that agriculture implies “intensi cation.” While the extensive technologies of the Paleolithic era allowed human populations to spread to new regions, the intensive technologies of the Agrarian era allowed more humans to live in a given area. This is why agriculture was able to start increasing the social “pressure” of human communities, just as gravity increased the pressure within the solar nebulae of early stars.

Larger, denser communities posed new problems and created new opportunities. Human populations grew rapidly as humans acquired more energy and resources. Human communities became larger. Even the earliest forms of farming could support 50–100 times as many people as foraging technologies from the same area (Christian, Maps of Time, pp. 208–09).

Larger, denser communities generated new forms of power and hierarchy because they required new rules to prevent con ict. They also stimulated collective learning and innovation by increasing the amount of people exchanging information and ideas. These changes accelerated change and transformed human societies. Niles Eldredge writes, “Agriculture represents the single most profound ecological change in the entire 3.5 billion-year history of life” (Eldredge, “The Sixth Extinction”).

This lecture has discussed what agriculture is and why its impact was so revolutionary. The next lecture tries to explain why it appeared when it did in a number of different parts of the world, from about 10,000 years ago.

Essential Reading

Christian, Maps of Time, chap. 8. Fagan, People of the Earth, chaps. 7, 8. Ristvet, In the Beginning, chap. 2.

Supplementary Reading

Questions to Consider

Bellwood, First Farmers. Mithen, After the Ice.

1. What is agriculture?

2. Why does the appearance of agriculture count as one of the fundamental thresholds of complexity in this course?