Evolution
BY NATURAL SELECTION
Paving the road for Darwin …
Georges Cuvier
◦Reconstructed organisms from fossilized
bones
◦Some organisms have changed over time
◦Some organisms have gone extinct
Prehistoric shark
Paving the road for Darwin …
Charles Lyell (geologist)
◦Archbishop Usher
◦ Earth was created 10.26.4004 BCE @ 9
a.m.
◦Lyell studied erosion patterns
◦Geological change is an extremely
slow, uniform process
◦Earth is very old
Paving the road for Darwin …
Thomas Malthus
◦Contended that population
growth would surpass food
supply/resources
◦Famine, disease, and war would
bring population back into
balance with resources
Paving the road for Darwin …
Lamarck’s Hypothesis of Evolution
◦Organisms constantly strive to
improve themselves
◦The most-used body structures
develop, unused structures waste
away
◦ The Principle of Use and Disuse
Paving the road for Darwin …
Lamarck’s Hypothesis of
Evolution
◦ Once a structure has been
modified by use or disuse, the
modification is inherited by the
offspring
◦ The Inheritance of Acquired
Characteristics
Paving the road for Darwin …
August Weismann
◦ Disproved LaMarck’s
hypothesis
◦ Experiment with mice  cut
off their tails
◦ Concluded that changes during
an individual’s lifetime DO NOT
affect reproductive cells or
offspring
Paving the road for Darwin …
Voyage of the HMS Beagle
◦ Stopped in Galapagos Islands
◦ 500 miles off coast of Ecuador
Paving the road for Darwin …
Voyage of the HMS Beagle
◦ Succession of species
◦ Armadillos are native to the Americas,
with most species found in South
America
◦ Glyptodont fossils are also unique to
South America
Why should extinct
armadillo-like species
& living armadillos be
found on the same
continent?
Mylodon (left) Giant
ground sloth (extinct)
“This wonderful relationship
Modern sloth (above)
in the same continent between
the dead and the living will…throw more light
on the appearance of organic beings on our earth,
and their disappearance from it,
than any other class of facts.”
Paving the road for Darwin …
Voyage of the HMS Beagle
◦ Unique species …
Paving the road for Darwin …
Voyage of the HMS Beagle
◦ Birds and more birds …
◦ Thought they were all different types of
birds
warbler
sparrow
woodpecker
finch
Paving the road for Darwin …
Voyage of the HMS Beagle
◦ Amazed to find out all 14 species of
song birds were finches
◦ Only 1 species of finch on the mainland
Warbler
finch
Small ground
finch
How did
one species
of finches become
so many different
species now?
Woodpecker
finch
Vegetarian tree
finch
Paving the road for Darwin …
Darwin’s Finches
Thinking of “family trees”
Descendant
species
Ancestral
species
Seed
eaters
Flower
eaters
Insect
eaters
Rapid speciation:
new species filling new niches,
because they inherited
successful adaptations.
Adaptive radiation
Paving the road for Darwin …
Darwin’s Finches
Differences in beaks
◦ Associated with eating different foods
◦ Survival &
Warbler finch
Cactus finch
reproduction of
Woodpecker finch
beneficial
adaptations to Small insectivorous
tree finch
foods available
Large
Cactus
on islands
insectivorous
eater
tree finch
Insect eaters
Sharp-beaked finch
Small ground
finch
Medium
ground finch
Seed eaters
Vegetarian
tree finch
Bud eater
Large
ground finch
Paving the road for Darwin …
Darwin’s conclusions
Small population of original South American finches landed on
islands
◦ Variation in beaks enabled individuals to gather food successfully in
the different environments
Over many generations, the populations of finches changed
anatomically & behaviorally
◦ Accumulation of advantageous traits in population
◦ Emergence of different species over time
Seeing this gradation &
diversity of structure in
one small, intimately related group of birds,
one might really fancy that
from an original paucity of birds
in this archipelago,
one species has been taken &
modified for different ends.
Paving the road for Darwin …
Darwin’s finches
Differences in beaks allowed
some finches to …
◦ Successfully compete
◦ Successfully feed
◦ Successfully reproduce
◦ Pass successful traits onto their
offspring
Paving the road for Darwin …
More observations
in the Galapagos
Correlation of
species to food
source
Whoa,
Turtles, too!
Paving the road for Darwin …
Artificial selection
◦ Not just a process from the
past …
◦ It’s all around us today
Paving the road for Darwin …
Selective breeding
the raw genetic
material (variation)
is hidden there
Paving the road for Darwin …
Selective breeding
Hidden variation
can be exposed
through selection!
Putting it all together …
Returned to England in 1836
◦ Wrote papers describing his collections & observations
◦ Long treatise on barnacles
◦ Draft of his theory of species formation in
1844
◦ Instructed his wife to publish this essay upon
his death
◦ Reluctant to publish, but didn’t want these
ideas to die with him
And then came the letter …
In 1858 Darwin received a letter from Alfred Russel Wallace
Alfred Russel Wallace
a young naturalist working
in the East Indies, had
written a short paper with a
new idea. He asked Darwin
to evaluate his ideas and
pass it along for publication.
And then came the letter …
To Lyell—
Your words
have come true
with a vengeance…
I never saw a more striking
coincidence…so all my originality,
whatever it may amount to,
will be smashed.
November 24, 1859, Darwin published
“On the Origin of Species by Means of Natural Selection”
Natural Selection
1. Variation exists in populations
Natural Selection
2. Over-production of offspring
More offspring are produced than the
environment can support
Natural Selection
3. Competition
For food, mates, nesting sites, escaping predators
Natural Selection
4. Differential survival
Successful traits =
adaptations
Natural Selection
5. Differential reproduction
Adaptations become more common in population
LaMarck vs Darwin
LaMarck
◦ In reaching higher vegetation,
giraffes stretched their necks &
transmitted that acquired
longer neck to offspring
Darwin

◦ Giraffes born with longer necks
survived better & left more
offspring who inherited the
longer necks
Evidence of Natural Selection
Peppered moths
Light vs dark variants
Year
1848
1895
1995
% dark
5
98
19
% light
95
2
81
Evidence of Natural Selection
Peppered moths
What was the selection factor?
◦ Early 1800’s = pre-industrial England
◦ Low pollution
◦ Lichen growing on trees = light colored bark
◦ Late 1800’s = industrial England
◦ Factories = soot coated trees
◦ Killed lichen = dark colored bark
◦ Mid 1900’s = pollution controls
◦ Clean air laws
◦ Return of lichen = light colored bark
◦ Industrial melanism
Evidence of Natural Selection
Insecticide & drug resistance
◦ Insecticides don’t kill all individuals
◦ Resistant survivors reproduce
◦ Resistance is inherited
◦ More of population is resistant
Pesticide
molecule
Target site
◦ Insecticide becomes less & less effective
Resistant
target site
Insect
cell site
Target
membrane
Decreased number of target sites
Evidence of Natural Selection
Genome sequencing
What can data from whole genome
sequencing tell us about evolution of
humans?
Evidence of Natural Selection
Primate Common Ancestry?
Chromosome Number in the
Great Apes (Hominidae)
orangutan (Pogo)
gorilla (Gorilla)
chimpanzee (Pan)
human (Homo)
Hypothesis:
Change in chromosome number?
If these organisms share a common
ancestor, then is there evidence in the
genome for this change in chromosome
number
48
48
48
46
Could we have
just lost a pair of
chromosomes?
Evidence of Natural Selection
Chromosomal
fusion
Testable prediction:
If common ancestor had 48 chromosomes (24 pairs),
then humans carry a fused chromosome (23 pairs).
Ancestral
ChromosomesFusion
What we should find:
Chromosome Number in the
Great Apes (Hominidae)
Testable!
This is what makes
evolution science
& not belief!
orangutan (Pogo)
gorilla (Gorilla)
chimpanzee (Pan)
human (Homo)
48
48
48
46
Homo sapiens
Inactivated
centromere
Telomere
sequences
in middle of
chromosome
Centromere: bonding point between
chromosomes
Telomere: at ends of chromosomes
Evidence of Natural Selection
What we
found …
Ancestral
ChromosomesFusion
Chromosome 2 in
Homo sapiens
Inactivated
centromere
Well I’ll
be a monkey’s
…or an ape’s…
uncle!
Telomere
sequences
in middle of
chromosome
“Chromosome 2 is unique to the human lineage
of evolution, having emerged as a result of
head-to-head fusion of two chromosomes that
remained separate in other primates. The
precise fusion site has been located in 2q13–
2q14.1, where our analysis confirmed the
presence of multiple subtelomeric duplications
to chromosomes 1, 5, 8, 9, 10, 12, 19, 21 and 22.
During the formation of human chromosome 2,
one of the two centromeres became inactivated
(2q21, which corresponds to the centromere
from chimp chromosome 13) and the
centromeric structure quickly deterioriated.”
Human Chromosome #2 shows the exact point
at which this fusion took place
Any Questions?