THE EVOLUTIONARY STORY OF HOMO SAPIENS 561
Domestication is an evolutionary process, by which plant and
animal species used by humans become different from their
wild ancestors. The earliest domesticated species is the dog,
which had evolved from wolves by 16 Kya in Eurasia—al-
though where and how is controversial [39, 54]. After that, the
earliest evidence of domesticated plants and animals dates
from about 11 Kya (possibly 13 Kya), in the Middle East, one of
several areas in which plant cultivation arose (TABLE A1) [62].
Archaeological and genetic approaches provide evidence
on the time and place of origin and subsequent spread of
domestic forms, on gene exchange with wild relatives, and
on the evolution of distinctive traits [17]. It is thought that in
most cases the earliest stages of domestication were more
accidental than deliberately planned. Wolves may in effect
have domesticated themselves by natural selection of less
fearful individuals that lurked near humans to eat food scraps.
Their descendants, dogs, may represent the commensal
pathway to domestication [38]. Most domesticated ungu-
lates, such as goat, sheep, and cattle, were initially hunted as
prey, and may have been held captive and bred in order to
supplement overhunted natural prey. Camels, horses, and
asses (donkeys), which were domesticated later, may have
been deliberately bred as beasts of burden. (Honeybeesand silkworm moths probably were also domesticated de-
liberately.) In most domesticated animals, a key selected trait
was behavior: domesticated forms are tame, not fearful.
In most species, the various familiar breeds were devel-
oped, largely by deliberate selection, only in the last 300
years, long after the original domestication process. Genom-
ic studies show that some genes were positively selected
(e.g., color in pigs). Domestication of many species involved
a reduction in effective population size, allowing many
slightly deleterious alleles to drift to high frequency. This has
resulted in reduced reproductive fitness and increased sus-
ceptibility to diseases that are features of most domesticated
animals and plants [79].
Many crop plants display similar, convergently evolved
“domestication traits” [62]. These include large seeds (which
can grow when deeply buried by plowing) and ready
germination (in contrast to the obligate seed dormancy in
most wild ancestors). Harvesting and replanting cereals,
such as wheat and rice, automatically selects for seeds that
remain attached to the plant rather than dropping off before
harvest. This makes the plant dependent on humans for seed
dispersal and germination.BOX 21A
Domesticated Plants and Animals
TABLE A1 Where and when some species were domesticatedREGIONDATE
(thousands of years ago)
PLANTS
ANIMALS
Eurasia 16 Dog
Western Asia (Middle East) 11–10 Wheat, barley, lentil, chickpea Goat, sheep, cattle, pig, cat
China 10.5 Rice, millets
Mexico 10 Corn (maize), squash, peppers
New Guinea 10 Taro, yam, banana
Central Andes 10 Squash, potato, quinoa
Amazonian South America 8 Manioc, peanut
Sahel (Africa) 7 Sorghum
Eurasian steppe 6 Horse
Southern Asia 6 Water buffalo, cattle
Andes 6 Llama
North America 5 Squash, sunflower
Northeast Africa 5 Ass (donkey)
Asia 5 Camels (2 species)
Andes 5 Guinea pig
Southeast Asia 5.5 Chicken
Tibet 4 Ya k
Northern Eurasia 2 Reindeer
Sources: [38, 62, 69, 79].21_EVOL4E_CH21.indd 561 3/22/17 1:51 PM