THEORY OF EVOLUTION
Other Mechanisms of
Change
WHAT ARE WE LEARNING TODAY?
Benchmarks
Learning Objectives
 SC.912.L.15.13 – Describe the
 I will explain and describe
conditions required for natural
how mutation and genetic
selection, including: overproduction
recombination increase
of offspring, inherited variation, and
genetic variation.
the struggle to survive, which result in  I will explain and describe the
differential reproductive success.
scientific mechanisms, such
 SC.912.L.15.15 – Describe how
as genetic drift, gene flow,
mutation and genetic recombination
and nonrandom mating,
increase genetic variation.
resulting in evolutionary
change.
 SC.912.L.15.14 – Discuss
mechanisms of evolutionary change
other than natural selection, such as
genetic drift and gene flow.
WHAT ARE OTHER MECHANISMS OF
EVOLUTION?

Evolution is the change in a
population’s genetic material over
generations.

Four other mechanisms of
evolutionary change exist besides
natural selection.

Mutations

Gene flow

Genetic drift

Nonrandom mating
WHAT ARE MUTATIONS?

A mutation is a change in the
genetic material of a cell.

Mutations affect evolution by
producing totally new alleles.

Germ mutations occur in the
reproductive cells, or gametes, of an
individual.

These mutations can be passed
on to the offspring.

They can affect the survival of an
individual organism or a genetic
line of organisms.
WHAT ARE MUTATIONS?

Mutations can be:
1. Neutral- No affect
• No pattern of increase
or decrease in allele
frequency
2. Harmful
• Usually naturally
selected against and
rid of in short time
3. Beneficial
• usually increase over
time
WHAT IS GENE FLOW?
Gene flow is the process of
genes moving from one
population to another.
 Gene flow can occur through
 Immigration ( the
movement of individuals
into a population)
 Emigration (the
movement of individuals
out of a population)

WHAT IS GENETIC DRIFT?
Genetic drift is the
process by which alleles
frequencies in a population
change as a result of
random events, or chance.
 It can result in substantial
changes within a
population.
 Only significant in small
and medium-sized
populations.

WHAT IS NONRANDOM MATING?
Nonrandom mating
occurs whenever
individuals may
choose partners.
 Influenced by
geographic proximity
and assortative mating
 Sexual selection
occurs when certain
traits increase an
individual’s success at
mating.

REVIEW
We have discussed how evolution by natural selection works
• NATURAL SELECTION requires:
1.
2.
3.
4.
Overproduction of offspring
Inherited Variation
Struggle to survive
Differential Reproduction
• We have discussed several ways natural selection can act on
populations
•
•
•
•
*Genetic drift
Gene flow
Mutations
Non-random mating
You should be able
to explain/describe
each of these
concepts by now
LETS GO OVER GENETIC DRIFT AGAIN
• Genetic Drift is a RANDOM change in allele frequencies in a
population due to a completely random event
• 2 types of Genetic Drift Situations:
1. Bottleneck effect
1. Founder’s effect
GENETIC DRIFT: BOTTLENECK EFFECT
Sometimes a random disaster may kill many individuals in a
population.
Those alleles left may not be the same representation as
the original population
GENETIC DRIFT: FOUNDER’S EFFECT
Migration of a small subgroup from a main population leads to a
difference in allele frequencies from the original population’s
The founding population will reproduce and pass on the
alleles of the founders
RATES OF EVOLUTION: PUNCTUATED
EQUILIBRIUM VS GRADUALISM
Gradualism
• Small changes occurring little by
little
• Usually hard to notice over short
period of time
Punctuated Equilibrium
• Change occurs in spurts
• Period of little change, followed
by period of huge change
• Change is noticeable and abrupt
• Change is slow, constant, and
consistent
Gradualism
Punctuated
Equilibrium
3 TYPES OF NATURAL SELECTION
1. Directional Selection
•
Better “fitness” toward 1 direction
•
Example: bigger the beak, the better fit
2. Stabilizing Selection
•
The intermediate trait is best fit
•
Example: the grey species is better fit than the white or
black
3. Disruptive Selection
•
the extreme, or outer end traits are better fit than the
intermediate trait
•
Example: the white and black species is better fit than the
grey species
3 TYPES OF SELECTION
MICROEVOLUTION VS MACROEVOLUTION
• Microevolution is evolution based on the genetic level
• Genetic drift
• Mutation
• Nonrandom mating
• Gene flow
• Macroevolution is evolution based on more visually observable
changes in species
• Extinction
• Speciation
• Adaptive radiation
• Convergent Evolution
• Co-evolution
EXTINCTION AND SPECIATION
• Extinction is when a species disappears forever from the earth as a
result to its population being completely diminished
• Speciation is the formation of new species from already existing
species
• But how do new species form?
•  Geographic isolation
• Temporal isolation
•  Behavioral isolation
Reproductive isolation New Species
REPRODUCTIVE BARRIERS
PRE- Reproductive Barriers
• Habitat Isolation
• Geographic isolation
• Temporal isolation
• Mechanical isolation
• Behavioral isolation
• Gametic (reproductive) islation
POST- Reproductive Barriers
• Hybrid Sterility
• Reduced Hybrid Viability
ADAPTIVE RADIATION
A single species evolves over a relatively short period of time into
several forms that live in different ways
Galapagos finches evolved different beaks and behaviors that
allow them to eat different kinds of food
CONVERGENT EVOLUTION
When distantly, unrelated species LOOK similar because they have
evolved in similar environments
CO-EVOLUTION
Sometimes 2 different species live and interact so closely together,
they evolve together
The evolution of one species drives the evolution of the other
EXAMPLE:
• Flowers and pollinators