Download Perpetuation of genes defines evolutionary fitness

http://www.pbs.org/wgbh/evolution/library/
11/2/quicktime/e_s_4.html
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Struggle for Existence & Survival of the fittest
◦ Because there are limiting resources (food, shelter,
competition, predation, etc…) organisms struggle
to survive.
◦ Organisms that are best suited for their
environment will have a better chance to survive
allowing them to reproduce and pass on their traits
that made them better suited for survival.

Fitness
◦ The contribution an individual makes to the gene
pool of the next generation, relative to the
contribution of other individuals in the population
◦ Those with higher fitness will make a greater
contribution to the gene pool; those with lower
fitness may not contribute to the gene pool at all

Type of natural
selection that favors
intermediate variants
by acting against
extreme population
Stabilizing Selection

Human birth weight is
usually in the range of
6.5lbs to 9lbs. Smaller
babies have increased
health risks. Larger
babies lead to health
risks for the mother.
Example

Type of natural
selection that acts
against the relatively
rare individuals at one
end of the phenotype
range.
Directional Selection

Pesticide resistance in
insects.
Example

Type of natural
selection that favors
extremes over
intermediate
phenotypes
Disruptive Selection

Coloration of African
Swallowtail – extremes
mimic unpalatable
species; most common
/ non-mimic becomes
easy prey
Example

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Sexual selection is natural selection for
mating success
It can result in sexual dimorphism, marked
differences between the sexes in
secondary sexual characteristics


Intrasexual selection is competition among
individuals of one sex (often males) for
mates of the opposite sex
http://youtu.be/Ez7RUSCUhzk
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Intersexual selection, often called mate
choice, occurs when individuals of one sex
(usually females) are choosy in selecting
their mates
Male showiness due to mate choice can
increase a male’s chances of attracting a
female, while decreasing his chances of
survival
http://youtu.be/W7QZnwKqopo