Download Natural selection

NATURAL SELECTION,
SEXUAL SELECTION &
ARTIFICIAL SELECTION
WHAT DO WE KNOW ABOUT NATURAL
SELECTION?
DEFINITION
• Natural selection: is one of the basic mechanisms of
evolution, it is the process in nature by which, according
to Darwin's theory of evolution, only the organisms
best adapted to their environment tend to survive and
transmit their genetic characters in increasing numbers
to succeeding generations while those less adapted
tend to be eliminated.
TYPES OF NATURAL SELECTION
• Stabilizing Selection: occurs when natural selection
favors the intermediate states of continuous variation
(results in a decrease of a population genetic variance).
Over time, the intermediate states become more
common and each extreme variation will become
less common or lost.
TYPES NATURAL SELECTION CONT..
• Directional selection: occurs when natural selection
favors one extreme of continuous variation (Effect:
there is a shift in genetic variance of the population for
a different phenotype). Over time, the favored extreme
will become more common and the other extreme will
be less common or lost.
TYPES NATURAL SELECTION CONT…
• Disruptive/Diversifying selection: occurs when natural selection
favors both extremes of continuous variation (increases genetic
variance when natural selection selects for two or more
extreme phenotypes that each have specific advantages). Over
time, the two extreme variations will become more common
and the intermediate states will be less common or lost.
Disruptive selection can lead to two new species.
EXAMPLE OF NATURAL SELECTION
WHAT TYPE OF NATURAL SELECTION IS THIS?
SEXUAL SELECTION
ARTIFICIAL SELECTION