Download Perpetuation of genes defines evolutionary fitness

13.16 to 13.18

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


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
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