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Evolution
Unit
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What is Evolution?
• Change in the genetic makeup of a population
over time.
• Fitness – those with favorable variations for
survival and reproduction.
– Populations can evolve, not individuals.
• Diverse gene pool good for long-term survival
of a species. Genetic variations are important!
• How do genetic variations occur?
– Mutation, sexual reproduction, artificial selection,
genetic technology
Genetic variation in a population
Essence of Darwin’s ideas
 Natural selection
heritable variation exists in populations
 over-production of offspring

 more offspring than the environment can support

competition
 for food, mates, nesting sites, escape predators

differential survival
 successful traits = adaptations

differential reproduction
 adaptations become more
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common in population
Lamarckian vs. Darwinian view
 LaMarck

in reaching higher
vegetation giraffes
stretch their necks &
transmits the acquired
longer neck to offspring

 Darwin

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giraffes born with longer
necks survive better &
leave more offspring who
inherit their long necks
Natural Selection
• Major mechanism of evolution
• Environment is always changing
• Acts upon the phenotype of the population
• Based on Darwin’s idea that resources are limited
and that there is competition for those resources.
• Adaptation = a genetic variation favored by
natural selection.
• When allele frequencies shift, speciation occurs
– Thus, the frequency change is NOT RANDOM
Effects of Selection
 Changes in the average trait of a population
DIRECTIONAL
SELECTION
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giraffe neck
horse size
STABILIZING
SELECTION
DISRUPTIVE
SELECTION
human birth weight
rock pocket mice
Natural selection
in action
Resistance…
NOT immunity!
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MRSA
Hidden variations can be exposed through selection!
Terminal
bud
Lateral
buds
Cabbage
Artificial selection
Brussels
sprouts
Leaves
Flower cluster
Kale
Cauliflower
Stem
Flower
and
stems
Broccoli
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Wild mustard
Kohlrabi
In addition to natural
selection, evolutionary
change is also driven
by random processes…
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Genetic Drift
 Chance events changing frequency of
traits in a population

not adaptation to environmental conditions
 not selection

founder effect
 small group splinters off & starts a new colony
 it’s random who joins the group

bottleneck
 a disaster reduces population to
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small number & then population
recovers & expands again but
from a limited gene pool
 who survives disaster may be random
Ex: Cheetahs
 All cheetahs share a small number of alleles
less than 1% diversity
 as if all cheetahs are
identical twins

 2 bottlenecks

10,000 years ago
 Ice Age

last 100 years
 poaching & loss of habitat
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Conservation issues
 Bottlenecking is an important
Peregrine Falcon
concept in conservation
biology of endangered
species
loss of alleles from gene pool
 reduces variation
 reduces adaptability

Breeding programs must
consciously
outcross
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Golden Lion
Tamarin
Human Impact on variation
 How do we affect variation in other
populations?

Artificial selection/Inbreeding
 Animal breeds

Loss of genetic diversity
 Insecticide usage

Overuse of antibiotics
 resistant bacterial strains
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2006 Fossil Discovery of Early Tetrapod
“Tiktaalik”
“missing link” from sea to land animals
Evidence Supporting Evolution
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Evidence for Evolution
• Paleontology – fossils show change in a
•
•
species over time
Biogeography – Similar species are found in
similar ecosystems around the world
Morphology – Comparing structures
–
–
Homologous structures – body parts with
similar structure but possible different
function. Shows common ancestry
Analogous structures – similar structure
develops in organisms that share a common
ecosystem but not a common ancestry
• Biochemical or Molecular
–
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Similarities in gene sequences, proteins, DNA
Fossils
 Preserved remains of living things
 Paleontology is the study of the fossil

record
Most organisms do not leave a fossil after
death

Explains the “missing links”
 Sedimentation Fossils

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As the organism decomposes the
spaces will be filled with the minerals
from the silt
The Archaeopteryx Fossil
Reptilian Features
Avian Features
Forelimb has three
functional fingers
with grasping
claws.
Vertebrae are
almost flatfaced.
Lacks the
reductions and
fusions present in
other birds.
Breastbone is small
and lacks a keel.
True teeth set in
sockets in the jaws.
The hind-limb girdle
is typical of
dinosaurs, although
modified.
Long, bony tail.
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Impressions of
feathers attached
to the forelimb.
Belly ribs.
Incomplete fusion
of the lower leg
bones.
Impressions of
feathers attached
to the tail.
LEFT: Archaeopteryx lithographica
Found in 1877 near Blumenberg, Germany
How old is that fossil?
 Relative Dating

Age of fossils based according to their location
in strata
 Absolute Dating




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Age of fossils determined by analyzing the
content of radioactive isotopes found in the
fossil.
Half-life: The length of time required for half of
the radioactive elements to change into another
stable element.
Unaffected by temperature, light, pressure, etc.
All radioactive isotopes have a dependable half
life. Ex: C14 decays into N14
Relative Dating
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Homologous Structures
Anatomical evidence
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Analogous structures
Convergent
Don’t
be fooled
by evolution
their looks!
Those
tails
Does fins
this &
mean
& sleek
they bodies
have a are
recent
common
ancestor?
analogous
structures!
Solving a similar problem with a similar solution
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Vestigial organs
Why would whales
have pelvis & leg bones
if they were always
secreatures?
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These are
remnants of
structures that were
functional in
ancestral species
Coevolution
 Two or more species reciprocally
affect each other’s evolution

predator-prey
 disease & host
competitive species
 mutualism

 pollinators & flowers
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