Transcript NATURAL AND ARTIFICIAL SELECTION

Natural and Artificial Selection
The Role of "Fitness"
Fitness is important in
both natural and
artificial selection.
Fitness describes the
ability of an individual
to live successfully in its
environment

If most insects in a population
are black, but a few are born red,
the red ones would be more fit in
an environment of red rocks.
The black ones would stand out
and be spotted by predatory
birds, while the red ones would
be camouflaged and survive.

If the red ones lived to breed,
but most black ones did not,
the trait for red coloring
would rapidly spread in that
species' gene pool.
 Most of the surviving
population could be red
within a few generations.

Natural Selection

When a population's environment acts
on that population such that welladapted individuals thrive and poorly
adapted individuals die out, that's
natural selection.
Natural Selection cont…
For natural selection to occur,
there must be diversity -- that is, a
range of different traits -- within a
population.
 That variation must directly impact
individuals' ability to survive.

 Those
traits must be genetically
heritable in other words something
a parent can pass on to offspring.
Artificial Selection
Artificial selection is imposed
by humans on other organisms.
 People apply selective pressure
by choosing to modify particular
traits to achieve a purpose.
 As in selective breeding for pet
traits or increased yield and
nutritional value in plant foods.

Evolution of wild Mustard through
Domestication
In artificial selection humans are the
selective agents.
The many different varieties of
cruciferous plants were created by
humans through selective breeding of
genetically varied wild mustardplants.
 Individuals with desired genetically
characteristics were bred with each
other until their descendents became
distinctly different from the ancestor,
the wild mustard.

Artificially selected traits
do not necessarily improve
fitness, as with natural
selection, but rather
encourage a trait that is fit
for the purposes of people.
Concerns About Artificial Selection
 While
natural selection relies on
diversity and keeps the fittest
members of a population in direct
contact with the rest of their peers.
 Artificial selection removes the most
desirable members from the rest of
the population and encourages
standardization to the point where
diversity is no longer possible.
Because humans have
helped purebred dogs
survive and breed, for
example, some undesirable
traits like narcolepsy and
hip dysplasia have become
characteristic of particular
breeds.
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