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 inÀ 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 À owering plants and