Download Document

THEORY OF NATURAL
SELECTION
10.3 pg. 304
ARTIFICIAL SELECTION
Where humans change a species by
breeding it for certain traits.
Ex. Humans select traits that are favorable in
plants and animals, then breed only those
with the trait,
producing more
of that trait.
HERITABILIT Y
The ability of a trait to be passed down from
one generation to the next.
STRUGGLE FOR SURVIVAL
Resources are limited in a population,
limiting population growth.
Food, water, shelter, disease limit
population growth
Population – individuals of the same
species that live in an area
NATURAL SELECTION
Mechanism where individuals that have
inherited beneficial adaptations produce
more offspring than other individuals.
Nature is the selecting agent
FOUR MAIN PRINCIPLES OF NATURAL
SELECTION
1.
2.
3.
4.
Variation
Overproduction
Adaptation
Descent with modification
VARIATION
Heritable differences result from
differences in the genetic material of an
organism
Could be inherited from parent or the result
of a mutation
OVERPRODUCTION
Having more offspring raises the chance
that some will survive, but it also results in
more competition for resources
ADAPTATION
A certain variation may allow an individual
to survive better than other individuals.
More successful individuals are
“naturally selected” to live longer
and produce more offspring.
DESCENT WITH MODIFICATION
Over time, more individuals will have the
favorable trait in every following
generation, as long as environmental
conditions stay the same.
FITNESS
Fitness - The measure of the ability to
survive and produce more offspring relative
to other members of that population.
GENETIC
VARIATION
WITHIN
POPULATIONS
11 .1 pg. 329
GENETIC VARIATION
Why its beneficial…
A population with a lot of genetic variation
has a wide range of phenotypes.
A wide range of phenotypes means some
individuals can adapt with a changing
environment and survive.
GENETIC VARIATION
How its stored in a population…
Stored in a gene pool
 The combined alleles of all individuals in a
population
GENETIC VARIATION
How it’s measured…
Measured by allele frequency
 How common an allele is in a population
MUTATIONS
Random change in DNA of a gene
This can form a new allele, which can be
passed to offspring if in a reproductive cell,
increasing the variation in a gene pool
RECOMBINATION
Happens when new allele combinations
form in offspring.
Happens during meiosis
NATURAL
SELECTION IN
POPULATIONS
11 .2
NORMAL DISTRIBUTION
Frequency is highest in the middle
(mean) and decreases towards the
extreme ends.
A population follows
a normal
distribution when:
all phenotypes
provide an equal
chance of survival
MICROEVOLUTION
Microevolution - a change observed in
allele frequency in a population over
time.
Microevolution occurs on a small scale.
DIRECTIONAL SELECTION
Selection that favors phenotypes at one
extreme
Example:
Drug
resistant
bacteria
STABILIZING SELECTION
Selection that favors the intermediate
phenotype, it is most common
Example:
Wasps
DISRUPTIVE SELECTION
Selection that favors
both extremes
Example:
Buntings (species
of bird)
OTHER
MECHANISMS
OF EVOLUTION
11 .3 pg. 335
GENE FLOW
Definition: movement
of alleles from one
population to another
How it works: occurs when
individuals move between
populations
GENE FLOW
Lots of gene flow between populations 
 Increases genetic variation of receiving population &
keeps gene pools similar
Limited gene flow between populations 
 Two populations become more genetically different.
 Species could possibly evolve into two different
species.
GENETIC DRIFT
Definition: Change in allele frequencies due to
chance.
How it works: causes loss of genetic diversity
in a population.
GENETIC DRIFT
Key Terms
 Bottleneck Effect: occurs
after an event greatly
reduces the size of a
population
GENETIC DRIFT
Key Terms
 Founder Effect: occurs after a small number of
individuals colonize a new area.
GENETIC DRIFT
Negative Effects…
Population losses genetic variation
Population is less likely to have individuals
that can adapt to survive in changing
environment
Lethal alleles carried by heterozygous
individuals will become more common due to
chance.
SEXUAL SELECTION
Definition: occurs when certain traits increase
mating success.
How it works: Females are choosy about
mates, forcing mates to have certain traits
that will increase their mating success.
SEXUAL SELECTION
Types
 Intrasexual: involves competition among males;
whoever wins, wins the female.
 Bighorn sheep butting heads
 Intersexual: males display certain
traits that will attract the female
 Peacocks fanning tails
 Frigate Birds
SPECIATION THROUGH
ISOLATION
11 .5
REPRODUCTIVE ISOLATION
Occurs when members of a population
can no longer mate with each other
This is the final step in speciation…
SPECIATION
The rise of 2 or more species from 1
species. (splitting of species into
different species).
There are 3 reasons for speciation…
1. BEHAVIORAL ISOLATION
Behavioral Isolation is caused by
differences in…
Mating rituals
Chemical signals
Courtship songs/dances
2. GEOGRAPHIC ISOLATION
Geographic Isolation is caused by…
Physical separation
Distance between populations
3. TEMPORAL ISOLATION
Temporal Isolation exists when…
Timing of mating rituals is off
Timing can change because of seasons,
weather, time of day, etc.
PATTERNS IN EVOLUTION
11 .6 pg. 347
CONVERGENT EVOLUTION
Evolution towards similar characteristics in
unrelated species
 Ex. Birds and insects with wings
 Ex. Fins of sharks and dolphins
DIVERGENT EVOLUTION
When closely related
species evolve in different
directions and become
increasingly different.
 Due to different
environments
 Ex. Kit Fox and Red Fox
COEVOLUTION
Process in which two or more species evolve
in response to changes in each other.
COEVOLUTION
Beneficial Relationships: Acacia plant and
ants. Ants will hide in plants hollow holes and
sting potential predators.
COEVOLUTION
Evolutionary Arms Races: species respond to
pressure from the other through better
adaptations over generations.
EXTINCTION
Elimination of a whole species from Earth.
 Ex - Tasmanian tiger—known as a thylacine
EXTINCTION
Background Extinction: Occur
continuously at a slow rate; part of
the cycle of life.
Mass Extinction: Rare; operate at
a global level, occurring suddenly
due to a catastrophic event.
PATTERNS IN SPECIATION
Punctuated Equilibrium: speciation occurs
suddenly, not gradually and are followed by
long periods of little evolutionary change.
PATTERNS IN SPECIATION
Adaptive Radiation:
diversification of one
ancestral species in to
many descent species
(usually over a wide
range of environments)