From Wikipedia,
the free encyclopedia.
| Domestication |
Dogs and sheep were
among the first
animals to be
domesticated.
|
| Statistics |
US livestock
inventory figures for 2004
| Animal |
Number |
| Pigs |
58,901,001 |
| Cows kept for beef |
42,957,001 |
| Total cows |
52,099,000 |
| Total cattle |
94,233,000 |
| Edit this
table
here |
|
Domesticated
animals,
plants, and other
organisms are those whose
collective
behavior,
life cycle, or
physiology has been altered as
a result of their breeding and
living conditions being under
human control for multiple
generations. Humans have brought
these populations under their care
for a wide range of reasons: for
help with various types of
work, to produce
food or valuable
commodities (such as
wool,
cotton, or
silk), and to enjoy as
pets or
ornamental plants.
In a related way the notion of
domestication is used in
domestication theory that
describes the process of the
'taming' or appropriation of
technology by its users.
Process of domestication
There is debate within the
scientific community over how the
process of domestication works.
Some researchers give credit to
mutations outside of human
control for making some members of
a species more compatible to human
cultivation or companionship.
Others have shown that carefully
controlled
selective breeding is
responsible for many of the
collective changes associated with
domestication. Theorists also note
that
natural selection probably
played a role in the domestication
of some species. These categories
are not mutually exclusive and it
is likely that mutations,
selective breeding, and natural
selection have all played some
role in the process of
domestication throughout history.
The domestication of
wheat provides an example of
how mutation can play a key role
in the process. Wild wheat falls
to the ground to reseed itself
when it is ripe, but domesticated
wheat stays on the stem when it is
ripe. There is evidence that this
critical change came about as a
result of a random mutation near
the beginning of wheat's
cultivation. Wheat with this
mutation was much more useful to
farmers and became the basis for
the various strains of
domesticated wheat that have since
been developed.
The example of wheat has led
some to speculate that mutations
may have been the basis for other
early instances of domestication.
It is speculated that a mutation
made some
wolves less wary of humans.
This allowed these wolves to start
following humans to scavenge for
food in their garbage dumps.
Presumably something like a
symbiotic relationship
developed between humans and this
population of wolves. The wolves
benefited from human food scraps,
and humans may have found that the
wolves could warn them of
approaching enemies, help with
hunting, carry loads, provide
warmth, or supplement their food
supply. As this relationship
evolved, humans eventually began
to raise the wolves and breed the
types of dogs that we have today.
Other theorists have pointed out
that natural selection rather than
a random mutation could also be
used to explain this process.
Wolves that were more comfortable
eating food scraps near human
settlements would have had an
advantage over other wolves. They
would have been more likely to
survive and pass on their
tolerance of humans to the next
generation. Thus the process of
domestication would have started
naturally before any human
intervention or selective breeding
was involved.
Nonetheless, some researchers
maintain that selective breeding
rather than mutation or natural
selection best explains how the
process of domestication typically
worked. Some of the most
well-known evidence in support of
selective breeding comes from an
experiment by Russian scientist,
Dmitry Belyaev, in the 1950s. His
team spent many years breeding the
silver fox (Vulpes vulpes)
and selecting only those
individuals that showed the least
fear of humans. Eventually,
Belyaev's team selected only those
that showed the most positive
response to humans. He ended up
with a population of grey fox
whose behavior and appearance was
significantly changed. These foxes
no longer showed any fear of
humans and often wagged their
tails and licked their human
caretakers to show affection.
Despite the success of this
experiment, it is clear that
selective breeding cannot always
achieve domestication. Attempts to
domesticate several kinds of wild
animals in this way have failed
repeatedly. The
zebra is one example. The
historical process of
domestication cannot be fully
explained by any one principle
acting alone. Some combination of
mutation, natural selection, or
selective breeding has played a
role in the domestication of the
various species that humans have
come into close contact with
throughout history.
Domestication of animals
According to physiologist
Jared Diamond,
animal
species must meet six criteria
in order to be considered for
domestication:
- Flexible
diet — Creatures that are
willing to consume a wide
variety of food sources and can
live off less cumulative food
from the
food pyramid are less
expensive to keep in captivity.
Most
carnivores can only be fed
meat, which requires the
expenditure of many
herbivores.
- Reasonably fast
growth rate — Fast maturity
rate compared to the human life
span allows breeding
intervention and makes the
animal useful within an
acceptable duration of
caretaking. Large animals such
as
elephants require many years
before they reach a useful size.
- Ability to be
bred in captivity —
Creatures that are reluctant to
breed when kept in captivity do
not produce useful offspring,
and instead are limited to
capture in their wild state.
Creatures such as the
panda and
cheetah are difficult to
breed in captivity.
- Pleasant disposition — Large
creatures that are
aggressive toward humans are
dangerous to keep in captivity.
The
African buffalo has an
unpredictable nature and is
highly dangerous to humans.
-
Temperament which makes it
unlikely to
panic — A creature with a
nervous disposition is difficult
to keep in captivity as they
will attempt to flee whenever
they are startled. The
gazelle is very flighty and
it has a powerful leap that
allows it to escape an enclosed
pen.
- Modifiable
social hierarchy — Social
creatures that recognize a
hierarchy of dominance can be
raised to recognize a human as
its pack
leader.
A
herding instinct arguably aids
in domesticating animals: tame one
and others will follow, regardless
of chiefdom.
Domestication of plants
Given
agriculture's importance to
humans, the domestication of
plants is even more important than
the domestication of animals.
Plants were first domesticated
around
9000 BC in the
Fertile Crescent in the
Middle East. The first plants
domesticated were generally
annuals with large seeds or
fruits. These included certain
pulses such as
peas and grains such as
wheat.
The Middle East was especially
suited to these species; the dry
climate was conducive to large
seeds, and the variety of
elevations led to a great variety
of species. As it took place
humans began to move from a
nomadic
hunter-gatherer society to a
settled agricultural society. This
change would eventually lead, some
4000 to 5000 years later, to the
first city states and eventually
the rise of
civilization itself.
Domestication was gradual, a
process of trial and error that
occurred slowly. Over time
perennials and small trees began
to be domesticated including
apples and
olives. Some plants were not
domesticated until recently such
as the
macadamia nut and the
pecan.
In different parts of the world
very different species were
domesticated. In the
Americas
squash,
maize, and
beans formed the core of the
diet. In East Asia
rice, and
soy were the most important
crops. Some areas of the world
such as
Australia never saw local
species domesticated.
Over the millennia many
domesticated species have become
utterly unlike their natural
ancestors. Corn cobs are now
dozens of times the size of their
wild ancestors. A similar change
occurred between
wild strawberries and
domesticated strawberries.
See also:
Cultigen
Degrees of domestication
The boundaries between
surviving wild populations and
domestic
clades of elephants, for
example, can become vague. This is
due to their slow growth. Similar
problems of definition arise when,
for example, domesticated cats go
feral. A
classification system that can
help solve this confusion might be
set up on a spectrum of increasing
domestication:
- Wild: These species
experience their full life
cycles without deliberate human
intervention.
- Raised at
zoos or
botanical gardens: These
species are nurtured and
sometimes bred under human
control, but remain as a group
essentially indistinguishable in
appearance or behavior from
their wild counterparts. (It
should be noted that zoos and
botanical gardens sometimes
exhibit domesticated or feral
animals and plants such as
camels, dingoes, mustangs, and
some orchids.)
- Raised commercially:
These species are
ranched or
farmed in large numbers for
food, commodities, or the pet
trade, but as a group they are
not substantially altered in
appearance or behavior. Examples
include the
ostrich,
deer,
alligator,
cricket,
pearl
oyster, and
ball python. (These species
are sometimes referred to as
partially domesticated.)
- Domesticated: These
species or varieties are bred
and raised under human control
for many generations and are
substantially altered as a group
in appearance or behavior.
Examples include
dogs,
sheep,
cattle,
chickens,
guinea pigs and laboratory
mice.
This classification system does
not account for several
complicating factors:
genetically modified
organisms,
feral populations, and
hybridization. Many species
that are farmed or ranched are now
being genetically modified. This
creates a unique category because
it alters the organisms as a group
but in ways unlike traditional
domestication. Feral organisms are
members of a population that was
once raised under human control,
but is now living and multiplying
outside of human control. Examples
include
mustangs and probably the
Australian
dingo. Hybrids can be wild,
domesticated, or both: a
liger is a hybrid of two wild
animals, a
mule is a hybrid of two
domesticated animals, and a
beefalo is a cross between a
wild and a domestic animal.
A great difference exists
between a tame animal and a
domesticated animal. The term
"domesticated" refers to an entire
species or variety while the term
"tame" can refer to just one
individual within a species or
variety. Humans have tamed many
thousands of animals that have
never been truly domesticated.
These include the elephant,
giraffes, and bears. There is
debate over whether some species
have been domesticated or just
tamed. Some state that the
elephant has been domesticated,
while others argue the cat has
never been. One dividing line is
whether a specimen born to wild
parents would differ in behavior
from one born to domesticated
parents. For instance a dog is
certainly domesticated because
even a
wolf (genetically the origin
of all dogs) raised from a
pup would be very different
from a dog.
History of domestication
The first domestic animal was
probably the
dog, possibly as early as
10000 BC in the
Natufian culture of the
Levant. However there is
evidence of an association between
humans and
wolves going back 150000
years, and also some early
evidence of
beekeeping (in the form of
rock paintings) dates to
13,000 BC. The next three -
the goat, sheep and pig - were
domesticated around 8000 BC, all
in western Asia. However, there is
recent archaeological evidence
from Cyprus of domestication of a
type of
cat by perhaps 7500 BC: this
might make the cat second. The cow
followed around 6000 BC. The horse
was first domesticated (probably
in northern Russia) around 4000
BC. Local equivalents and smaller
species were domesticated from the
2500s BC.
The processes of domestication
and the distribution of
domesticated species were both
radically affected by the
establishment of regular contact
between the Eastern and Western
Hemispheres following the voyages
of
Christopher Columbus. This
sudden increase in the
transmission of organisms between
the Eastern and Western
Hemispheres is referred to as the
Columbian Exchange.
Limits of domestication
Despite long enthusiasm about
revolutionary progress in farming,
few crops and probably even fewer
animals ever became domesticated.
While the process continues with
plants (berryfruits, for example),
it appears to have ceased with
animals.
Domesticated species, when bred
for tractability, companionship or
ornamentation rather than for
survival, can often fall prey to
disease: several sub-species of
apples or cattle, for example,
face extinction; and many dogs
with very respectable
pedigrees appear prone to
genetic problems.
One side-effect of
domestication has been disease.
For example, cattle have given
humanity various
viral poxes,
measles, and
tuberculosis; pigs gave
influenza; and horses the
rhinoviruses. Humans share
over sixty diseases with dogs.
Many
parasites also have their
origins in domestic animals.
See also
