Lecture 24: Threshold 7—Agriculture
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.