EVOLUTION:
PROCESSES & PATTERNS
BIOLOGY EOC BENCHMARK
SC.9.12.L.15.1 Explain how the
scientific theory of evolution is
supported by the fossil record,
comparative anatomy, comparative
embryology, biogeography, molecular
biology, and observed evolutionary
change
VIDEO: Simpson Evolution
Why is Homer evolving?
Convergent Evolution
• Different organisms that
live in similar environments
become more alike in
appearance and behavior.
• Environment selects
similar adaptations in
unrelated species.
• Organisms develop
analogous structures
(same function, but
different origins)
Coevolution
• Two species evolve together.
• There is a mutual evolutionary influence between
two species.
• The species have a symbiotic relationship
(interaction between members of two
populations).
• Example: - Birds and flowers
Divergent Evolution
• Ancestral species gives
rise to a number of new
species that are adapted
to different environmental
conditions and are less
alike.
• Often occurs when a
species colonizes a new
environment.
• Also known as adaptive
radiation.
Evidence for Evolution
• Fossil Records
• Biogeography
• Comparative Anatomy and Embryology
• Genetics
• Experimental Research
Fossil Record
• Dating methods have shown the
age of the Earth – plenty of time
for evolution to occur.
• Recent fossil discoveries have
shown intermediate species,
connecting species in a series
• Dinosaurs  Birds
• Land mammals  Whales
• Fish  Four-legged land animals
Biogeography
• The study of where organisms and their ancestors lived.
• Patterns in the distribution of both living and extinct
species help us to understand how organisms evolved.
• Two kinds of patterns have been observed.
Biogeography
• Slight differences in environment produces variations
among populations that eventually result in different
species.
• Galapagos finches
• Chimps and bonobos
Biogeography
• Distantly related species that have similar traits often live
in similar geographical areas
Comparative Embryology
• Similar embryonic stage of organisms that are very
different as adults.
Anatomy
• Homologous Structures
• Analogous structures
• Vestigial Structures
Homologous Structures
• Structures that are shared by different species that have
been inherited by a common ancestor
• Animal Forelimbs
• Opposable thumbs in primates
• Hooves in ungulates
Analogous Structures
• Body parts that serve similar functions, but may not have
similar structures, that evolved independently from each
other.
• Wings of insects and birds
• Evidence of the effect of selective pressures
Fly wing
Bat wing
Vestigial Structures
• Body parts that have lost most or all of their original
function.
• Appendix in humans
• Femur in snakes
• Hip bones in dolphins
Genetics and Molecular Biology
Comparative Biochemistry
• Similar DNA sequences
• Similar gene segments of the
DNA
• code for similar traits
• closely related species
Experimental Research
• Is evolution testable?
• Galapagos finches – Studied for decades (>35 years)
• Drosophila (fruit flies) – reproduce very quickly
• Bacteria – antibacterial resistance
THE EVOLUTIONS OF POPULATIONS
THERE ARE FOUR
MECHANISMS THAT CAN GIVE
RISE TO EVOLUTION:
1.MUTATION
2.GENETIC DRIFT
3.MIGRATION (Gene Flow)
4.NATURAL SELECTION
Greatly and quickly seen in isolated populations like those on islands.
- Allele frequency will change over generations; situations/ENV will
favor one allele over another
- Those populations at equilibrium are not evolving
- Species with more genetic diversity will adapt better to
environmental changes
GENETICS OF WHITE BENGAL TIGERS
In nature, White Bengal tigers arises from the mating of two Bengal tigers with
recessive genes for the white color of fur. The gene is recessive and has the effect
that offspring (cubs / kittens) only become white if they inherit the recessive gene
from both parents.
It is the same principle as with brown and blue eyes. The inbreeding producing all
these White tigers is neither good nor healthy for the tigers. In nature White tigers
have, at least theoretically as there probably aren’t any, less of a chance of
surviving than normal colored tigers due to their lack of camouflage compared to
the normal Yellow Tigers.
Below is a very simplified illustration (Fig 1) of how the transfer of genes coding
for fur color works. Consider to yellow Bengal Tigers mating. If they are both
carriers of the recessive gene there's a 25 percent chance that their cubs will be
white. If a white and a yellow Bengal tiger mates there's a 50 percent chance that
the offspring will be white. The chances of getting more White tigers can be
enhanced by letting tigers that are related mate. This is and example of
inbreeding.
THE EVOLUTIONS OF POPULATIONS
TIGER POPULATION
Allele frequencies:
Proportion of orange furpigment alleles in the
population
Proportion of white fur-pigment
alleles in the population
Evolution is a change in the allele frequencies of a
population over time. For example, a change in the proportion
of pigment alleles in the population of tigers means that
evolution has occurred.
MUTATION
#1
A mutation can create
MECHANISMS
a new allele in an individual.
OF
When this happens, the
EVOLUTION
population experiences a
change in its allele
frequencies and,
consequently, experiences
evolution.
EVOLUTIONARY CHANGE: MUTATION
Mutagen
DNA
Normal basepair sequence
Mutated basepair sequence
Normal protein Mutated protein
 Despite mutation’s vital role in
the generation of variation,
mutations almost always cause
early death or lower the
reproductive success of an
organism.
Normal
phenotype
Mutated
phenotype
Mutations
• Are rare because you have
Brain Pop: Genetic Mutations
self correcting enzymes
• Natural Process that
produces genetic diversity
• Not all mutations are bad
• Some won’t affect the body
at all
• Blood types/ear lobes
• Some are advantageous
(thumb)
MECHANISM FOR EVOLUTION - GENETIC DRIFT
population can experience random changes in allele frequency that do
not influence reproductive success which leads to evolution
POPULATION BEFORE
GENETIC DRIFT
Allele frequencies:
cleft chin (dominant)
smooth chin (recessive)
Neither allele is
related to reproductive
success. Inheritance is
based solely on
chance.
POPULATION
AFTER GENETIC
DRIFT
There are now more
recessive alleles in
the population than
before.
REPRODUCTION
In this example, a heterozygous
couple (Cc) could have two
children that are homozygous
recessive (cc), causing an
increase in the proportion of
recessive alleles in the
FIXATION
population.
Genetic drift leads to fixation when an allele’s frequency
becomes 100% in a population. If this occurs, there is no
longer genetic variation for the gene.
GENETIC DRIFT - FOUNDER EFFECT
The founding members of a new population can have different allele frequencies
than the original source population and, consequently, the new population
experiences evolution.
SOURCE POPULATION
Allele frequencies:
5 digits per hand
(recessive)
>5 digits per hand
(dominant)
A group of individuals may leave a
population and become the
founding members of a new,
isolated population.
NEWLY FOUNDED
POPULATION
The new population will be
dominated by the genetic
features present in the
founding members.
AMISH
ARTICLE: The Amish and Founder Effect
GENETIC DRIFT - BOTTLENECK EFFECT
Occasionally, famine or disease or rapid environmental change may cause
the deaths of a large, random proportion of the individuals in a population.
SOURCE POPULATION
SOME CATASTROPHE
EXTREME AND RAPID
ENVIRONMENTAL CHANGE
NEW POPULATION
The new population will be
dominated by the genetic
features present in the
surviving members.
All cheetahs living today can trace
Unless more individuals are introduced to the
population, mating options will be limited thus
decreasing variation in the gene pool
(decreasing genetic diversity).
their ancestry back to a dozen or so
individuals that happened to survive a
population bottleneck about 10,000
years ago!
#3 MECHANISMS
MIGRATION (GENE FLOW)
1 BEFORE MIGRATION
Two populations of the same species exist in
separate locations. In this example, they are
separated by a mountain range.
Population 1
OF EVOLUTION
MIGRATION
After a group of
individuals migrates from
one population to another,
both populations can
experience a change in
their allele frequencies
and, consequently,
experience evolution.
Population 2
#3
MIGRATION (GENE FLOW)
2 MIGRATION
A group of individuals from Population 1 migrates over
the mountain range.
Population 1
MECHANISMS
OF EVOLUTION
MIGRATION
After a group of individuals
migrates from one
population to another, both
populations can experience
a change in their allele
frequencies and,
consequently, experience
evolution.
Population 2
#3 MECHANISMS
OF EVOLUTION
MIGRATION
After a group of individuals
migrates from one
population to another, both
populations can experience
a change in their allele
frequencies and,
consequently,
experience
reproduce in
evolution.
MIGRATION (GENE FLOW)
3 AFTER MIGRATION
The migrating individuals are able to survive and
the new population and they may experience evolutionary
changes from population 1.
Population 1
Population 2
#4
Mechanism of
Evolution
Natural Selection
1. VARIATION OF A TRAIT IN A POPULATION
Conditions that must
occur for Natural Selection
The tiniest dog in a litter has
reduced differential
reproductive success. Its
more robust siblings prevent
access to the food it needs to
grow and thrive.
3. One version of the trait must provide an
advantage over a different version of the trait.
2. The trait must be inheritable