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Artificial Selection at Work
What is artificial selection?
Artificial selection is
the intentional reproduction of individuals
in a population that have desirable traits. In organisms that
reproduce sexually, two adults that possess a desired trait — such
as two parent plants that are tall — are bred together. In
this example, the mechanisms of heredity dictate that the next
generation will consist of more tall plants than previous generations.
If artificial
selection is continued, all of the population will ultimately
be tall. Also called selective breeding, artificial selection
is perhaps
best understood as a contrast to natural selection, where the
random forces of nature determine which individuals survive
and reproduce. In both cases, the outcome is the same: a population
changes
over
time, so that certain traits become more common.
What are some
examples of artificial selection?
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Teosinte (left)
and its modern descendent, corn, a product of artificial
selection |
Artificial selection has generated
untold diversity in both plants and animals. In agriculture,
superior strains of corn,
wheat, and soybeans
have resulted from careful breeding. The Brassicas described
by Paul Williams in the video are great examples of artificial
selection. Cabbage,
broccoli, cauliflower, Brussels sprouts, collards, and kale are
all members of the same species, Brassica oleracea. Gardeners
have cultivated
flowers such as roses and orchids, carefully manipulating heredity
to produce the “perfect” hybrid.
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A variety of vegetables
of the
Brassica oleracea species
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Some consider domesticated
animals to be the ultimate products of artificial selection.
Thoroughbred racehorses are one example
of artificial selection of animals. The meats we eat are the
result of
the careful selective breeding of cows, pigs, sheep, and chickens.
Our pets are a far cry from their “wild” ancestors. Cats
and dogs, which were originally domesticated for pest control,
hunting, or shepherding, eventually were bred to become companion
animals. A
glance at a group of dogs — all of the species Canis familiaris — reveals
an astounding diversity of body type, size, and coloration.
There
can be a down side to artificial selection. Because this process
essentially removes variation in a population, selectively
bred organisms can be especially susceptible to diseases or changes
in the environment that would not be a problem for a natural
population. Inbreeding — the mating of closely related individuals — is
also a problem. In dogs, this has resulted in breeds that have
health issues ranging from decreased life span to hip dysplasia.
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