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Evolution
Chapters 16 & 17
Darwin’s Voyage
Chapter 16
Evolution
• Change over time
Charles Darwin
• Developed a scientific theory that explains
how modern organisms evolved over long
periods of time through descent from
common ancestors.
Darwin’s Voyage
• 1831: Darwin sailed around the world in the HMS
Beagle making observations and collecting
evidence.
• Most of his work was done at the Galapagos
Islands, located 100 km west of
South America.
• 1859: Darwin publishes Origin of
the Species.
Darwin’s Observations
1.) Different, yet similar, animal species
inhabited separated, but similar, habitats
around the globe.
2.) Different, yet related, animal species
occupied different habitats within a local area.
3.) Some fossils of extinct animals were similar
to living species.
Ideas that Shaped
Darwin
Public Perception
• All life was only a few thousand years
old.
• Since its creation, not much had
changed.
Scientists that Influenced Darwin
• (1785) James Hutton: Using geological examples,
concluded that the earth must be much older than a
few thousand years.
• (1798) Thomas Malthus: Reasoned that if the human
population grew unchecked, their wouldn’t be enough
space and food for everyone.
• (1830) Charles Lyell: Argued for uniformitarianism,
which holds that the geological processes we see today
must be the same ones that occurred long ago.
Jean Baptiste Lamark
• (1809) Published a theory on evolution that
suggested organisms could change during
their lifetimes by selectively using or not using
parts of their bodies. These acquired traits
could then be passed onto their offspring.
• What is wrong with this theory???
Natural Selection
Words to Know
fitness: the ability to survive and reproduce
adaptation: an inherited characteristic that
increases an organism’s chance of survival
• Adaptations increase an organism’s fitness.
Natural Selection
• AKA: survival of the fittest
• Selected traits increase an organism’s fitness.
• No human involvement. (Unlike selective
breeding.)
For Natural Selection to Occur:
1. The population must be limited in size, which
creates competition.
(Competition: when two organisms want the
same resource at the same time.)
2. Genetic variation (of inherited traits) must
exist.
Sources of Variation
3. This variation must affect the organism’s
reproductive success.
Recipe for Evolution
Descent with modification
• Species descend from other species over time.
Ex: dogs descended from wolves.
Common descent: all things, living and extinct have
common ancestors
Evidence of Evolution
Evidence of Evolution
1. Structural adaptations
A. Mimicry: one species resembles another species
B. Camouflage: species blend in with surroundings
Evidence of Evolution
2. Behavioral adaptations
a. Migration
b. Courtship
c. Defending or claiming territory
d. Cooperation (Ex: hunting in packs)
e. Kin selection: helping a relative survive because
they share the same genes
f. Communication (visual, chemical, sound,
language)
More evidence…
3. Fossils
4. Geographic Distribution of Species (similar,
but unrelated species live in different parts of
the world)
And more evidence…
5. Homologous structures: basic arrangement of
bones in body structures of different species
is similar
ex: bird wing and whale flipper
Note: Not to be confused with analogous structures
(have the same function, but different
structures)
And more evidence…
6. Vestigial structures: body structures that
serve no purpose in the present day
organism
ex: an ostrich’s wings
And more…
7. Similarities in early development.
8. Biochemistry: comparing the DNA and RNA
All Living Things are
Related
Evolution
Misconceptions
Evolution of Populations
Chapter 17
Populations, NOT individuals evolve!
Gene pool: all of the alleles of a population’s genes
Relative frequency = # certain allele x 100%
total # alleles
Ex: attached earlobes
***Let’s calculate this for our class!
Genetic equilibrium: when the relative frequency remains
the same over several generations
• If the relative frequencies in a gene pool change,
EVOLUTION has probably occurred!
Sexual vs. Asexual Reproduction
• The two main sources
of genetic variation in
sexually reproducing
organisms is through
mutations and genetic
recombination.
• The main source of
genetic variation in
asexually reproducing
organisms is through
mutations only.
Natural Selection on Single Gene Traits
12
14
10
12
10
8
Hands Up
8
Hands Up
Hands
Down
6
Hands
Down
6
4
4
2
2
0
0
Before the Predator
After the Predator
Natural Selection on Polygenic Traits
• Because a polygenic trait is
controlled by more than one
gene, a wide spectrum of
phenotypes are observed.
***Let’s calculate this for our
class using height.
• Three types of natural
selection:
– Directional
– Stabilizing
– Disruptive
Average Height
7
6
5
4
Average
Height
3
2
1
0
150 160 165 170 180
cm cm cm cm cm
Directional Selection
• Natural selection favors
one of the extreme
variations of the trait,
so the entire graph
moves.
• Ex: height, beak lengths
Stabilizing Selection
• Natural selection that
favors the average
individuals in a
population.
• Ex: birth weight
Disruptive Selection
• Individuals with either
extreme variation are
selected for. (The
average drops.)
• Ex: Light and dark
colored limpets
Speciation
• Occurs when members
of the same population
can no longer
interbreed to produce
fertile offspring.
• Can occur from
geographic, behavioral
or reproductive
isolation.
Divergent vs. Convergent Evolution
Divergent evolution:
Convergent evolution:
members of one species
members of different
become less and less
species evolve similar
alike, eventually
traits because of their
resulting in separate
environment.
species
The Effect of Small Populations
Genetic drift: a change in allele frequencies due
to something other than natural selection
Ex: Ashkenazi Jews, the Amish, the Holocaust
Specific types of genetic drift are…
Founder effect: a small group starts a new
population elsewhere and their particular
genes become prevalent
Bottleneck effect: a natural disaster drastically
reduces the population