82 DISCOVERMAGAZINE.COMDISCOVER (ISSN 0274-7529, USPS# 555-190) is published monthly, except for combined issues in January/February and July/August. Vol. 38, no. 8. Published by Kalmbach Publishing Co., 21027 Crossroads Circle, P.O. Box
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53187-1612. Printed in the U.S.A.Animal Domestication
20 Things You Didn’t Know About ...
BY GEMMA TARLACH12 It wasn’t until 2014, however, that researchers
offered a single explanation for the phenomenon
of floppy ears, smaller teeth, tameness and other
“domestication syndrome” traits: a mild deficit in
neural crest cells. 13 In vertebrate embryos, neural
crest cells (NCCs) form along the dorsal side, or crest,
of the neural tube (the proto-central nervous system).
14 NCCs spread through the embryo as it develops,
and directly or indirectly affect a range of other
functions, from the adrenal gland, which controls
the fear response, to pigmentation, which can differ
between domesticated and wild populations. 15 Also
different between the two populations: the speed of
development. Domesticated animals develop more
slowly, so their NCCs spread at a slower pace, having
minimal or no effect on the function they typically
target. It’s that deficit that results in domestication
syndrome. 16 Subsequent genetic studies have
supported the NCC deficit hypothesis, most recently
an April report in Science on the sequencing of 14
ancient horse genomes up to 4,100 years old; that’s
close to the estimated dawn of domesticated horses
some 5,500 years ago. 17 Sheep were domesticated
twice as long ago as horses, with goats (10,500
years ago), pigs and humpless cattle (both about
10,300 years ago) hot on their heels. 18 Dogs have
the distinction of being the first animal humans
domesticated — and the only one before the advent
of agriculture. A 2016 paleogenetic study found two
doggie domestication events perhaps 14,000 years
ago: one in Europe and a second in East Asia. The
latter population eventually spread west and replaced
the former. 19 There’s genetic evidence for a similar
double domestication in cats, too. In June, a study
in Nature Ecology & Evolution found the African
wildcat Felis silvestris lybica was first domesticated
regionally in the Near East before 4400 B.C. 20 But
a second domestication in ancient Egypt, before the
first millennium B.C., proved more successful: This
later lineage spread rapidly around the world via land
and sea trade routes — and eventually took over the
internet. Who’s the boss now?^ DGemma Tarlach is senior editor at Discover.1 Which came first, the chicken or the egg? That’s
easy: eggs. Microfossil embryos in primitive eggs
from southern China are about 600 million years
old. 2 The chicken, however, now the world’s
most common domestic animal, dates back
a mere 4,000 or so years. Most researchers
believe that Gallus gallus, the red jungle fowl,
was first domesticated in East or Southeast
Asia. 3 In 2014, a study ruffled feathers
with claims that bones from northern China
showed the wild G. gallus had been chick-
enized into G. gallus domesticus about 10,000 years
ago. 4 But critics suggested the 2014 paper
really laid an egg: The bones purported to
be from chickens were, they claimed, from
pheasants and possibly even dogs. 5 The
word domestication is itself contentious.
Some definitions focus on genetic changes
due to selective breeding; others describe
it as humans removing an animal from
its natural environment to control its
entire life cycle. 6 A 2015 study offered a
broader definition: a mutually beneficial
relationship, over generations, between
one organism influencing reproduction
and care of another. 7 The study didn’t
specify humans as the domesticator
because these relationships can exist
beyond our sphere, such as numerous species of
ants that farm fungus or herd aphids. 8 Although
researchers traditionally used archaeological evidence
to determine when our species domesticated another,
DNA can also show when a population went from
wild to mild. 9 By comparing ancient and modern
DNA from a domesticated animal as well as its
nearest wild relatives, researchers can identify when
specific genetic mutations associated with domes-
tication arose. 10 Some of the earliest and most
common genetic markers for domestication involve
changes in the endocrine system that make an animal
less fearful of humans. 11 In 1868, Charles Darwin
was the first to document a collection of physical
and behavioral traits seen in domestic animals,
particularly mammals, but not their wild relatives.From top: Humans
domesticated the red
jungle fowl at least
4,000 years ago, and
the dog 10,000 years
or more before then.
Humans aren’t the
only domesticators,
however. Formica
aerata is just one
of a number of ant
species that herd
aphids.
FROM TOP: FEATHERCOLLECTOR/ISTOCK; WILLIAM ZUBACK/DISCOVER; ALEX WILD