Evolution by Means of Natural
Selection: The Development of
Adaptations to Survive
Slide # 2
Important Vocabulary
1. Fit or Fitness: success at
surviving & reproducing
2. Gene Pool: all alleles (forms
of genes) shared within a
species
3. Frequency: how often an
allele is seen in the gene pool
a.
How does its coloration
help the Snowy Owl
survive in its habitat?
b.
What other adaptations
does it have that makes it
“fit” for its environment?
Coevolution verses Convergent Evolution
Coevolution
Convergent evolution
1. Two species evolve in
response to each other.
2. Examples:
predator/prey
host/parasite species
bees & flowers
1. Different lineage, exposed to
similar selection pressures
2. Example:
Bats and butterflies. Evolved
through different mutations.
3. Convergent evolution produces
analogous structures (similar
in function, different in structure
(bat's wing and butterfly's wing).
Slide # 4
Requirements for Natural Selection: Variation
Exists in Nature
a. Variation is inheritable
b. New variations come
from mutations in DNA.
c. Some mutations are
harmful & some are
helpful.
Slide # 5
Requirements for Natural Selection: More
offspring are produced than will survive.
a. Tendency towards
overpopulation
b. Strategy for survival:
Many species lay
tons of eggs; some
will survive to
adulthood
Slide # 6
Requirements for Natural Selection: There is a
constant struggle for survival.
a. Competition for limited resources food, space,
territory, shelter (nesting sites) & mates
Wolf chasing raccoon
Slide # 7
Requirements for Natural Selection: Some individuals in the
species will have variations that cause them to be the most fit
in a particular environment.
a. The fittest individuals will survive the longest & produce
more offspring than less “fit” individuals.
b. The most “fit” individuals are best adapted to that
particular environment.
c. If environment changes, different variations may be
selected to be more fit
Slide # 8
Requirements for Natural Selection: Vast amount of time
is required for a species to change
a. After many generations
there will be enough
genetic change in the
population to produce a
new species.
Separated by a glacier during
the last Ice Age, two different
species of meadowlark
evolved.
Eastern
Meadowlark
Western
Meadowlark
Slide # 9
Mutations in Genes: the Source of all new Variations
1. Helpful mutations lead to
adaptation by increasing fitness &
decreasing the death rate
• Frequency of helpful mutation
will increase in the population
as more individuals survive &
leave offspring
2. Harmful mutations decrease
fitness of the individual in that
environment & cause a higher
mortality rate
– Frequency of the mutation will
decrease & might or might not
disappear from the gene pool
How is the fruit fly on
the bottom different
from the fruits above?
Slide # 10
Helpful Mutations (Adaptations)
Adaptations of Birds Feet
The woodpecker’s sharp
beak allows it to drill into
trees to catch insects.
Slide # 12
Adaptations: A Result of Compromise
An adaptation may
work really great for
some things (reaching
food) , but they may
prose a problem for
other things (drinking
water)
Slide # 12
Camouflage: A Helpful Adaptation
1. Camouflage: having a shape / color that blends
in with the environment
2. Difficult for predators to see the prey
Find the canyon tree frog!
Find the green leaf mantid!
Slide # 13
Mimicry: Taking Advantage of Another’s Coloration
1. Mimicry: when a harmless individual looks
like a similar, harmful (poisonous) individual
2. Predators learn to avoid both
Viceroy: looks
poisonous monarch
Monarch is poisonous