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CHARLES DARWIN
Natural Selection Part 1
Who was he…
Charles Darwin was a medical student
who could not handle surgery. (He did
not like the sight of blood).
He joined the seminary
as a respectable profession
and spent a lot of time
outside as a naturalist.
H.M.S. Beagle
He had the opportunity to travel and
study organisms.
1831 He traveled from England to the
South American Coast for 5 years
Before he believed all organisms were
specifically created to match their
environment. (This was the common
belief held by the church).
He observed (drew) and collected many
species of organism at every port along
the way.
Example:
Finches from the
Galapagos Islands.
His observations…
He saw patterns in how similar animals
differed from each other. (Beak length)
He started to wonder could species
change over time to match their
environment??
The Finches…
The Galapagos finches looked similar
to South American Finches.
But they differed in their food types
The Questions…
Why did they not resemble other
Finches found on Islands similar to the
Galapagos, yet instead resembled the
Finches from mainland?
Shouldn’t all island birds resemble each
other? (If island birds were created for
islands.)
His Conclusions…
They must have migrated to the islands.
They Adapted…
For new food sources.
Evolution…
Definition-The change of an organism
over time.
Origin of a Species was written to
explain this idea.
He is accredited with the idea of
evolution.
The Mechanism…
Darwin needed a reason for evolution to
occur.
Thomas Malthus
Malthus is accredited with the idea that
humans reproduce faster then our food supply
can be replenished.
Darwin’s deduction:
competition=survival
Selections…
Darwin looked toward artificial selection
for his theory.
Artificial Selection – organisms are bred by
humans for traits that are helpful in its survival.
From this he came up with Natural
Selection.
Natural Selection – Organisms with traits well
suited for the environment are more likely to
survive and reproduce creating offspring with
those traits.
Eventually…
His theory was accepted because he
had a logical mechanism to support his
theory.
Now genetics helps prove it.
Darwin’s 5 Points
A population has variation.
Some variations are favorable.
More offspring are produced than
survive.
Those that survive will have favorable
traits.
A population will change over time.
Natural Selection Truths
Acts on individuals, but consequences
occur in populations.
Acts on phenotypes, but focuses on
gene frequency.
It is not forward looking.
It is not perfect for environment.
It is non random, but not progressive.
AGENTS OF
CHANGE
Mutations
An alteration of DNA
Ex. Point mutation - Sickle Cell
1-10 times/100,000 cell divisions
Gene Flow
The movement of alleles from 1
population to another.
Ex. Migration
Non Random Mating
Inbreeding
Increases homozygosity
Innate defense
1 gender leaves usually males
Outcrossing
Increases heterozygosity
Prevents complete extinction due to illness.
Genetic Drift
Loss of alleles
Founder Effect - small start up population
Bottleneck Effect - big population wiped
out.
Example. Cheetahs
Selection
Difference in survival between different
phenotypes.
Natural vs. Artificial
NATURAL SELECTION
Mechanism and Types
Key Factor
The factor most influencing what traits
are considered good or bad is… the
environment.
The environment determines essentially what
organisms with live and reproduce the most.
The traits that allow for organisms to
reproduce more will have a higher
frequency in the next generation.
So…the traits will become more common in
the organism.
Adaptation
Adaptation is the process in which
organisms become better suited to their
environment.
Ex. Light and Dark Peppered Moths
The dark moths became more common after the
Industrial Revolution.
Why?
Sickle Cell Anemia
Sickle Cell Anemia is a recessive
disease originating in Africa.
1 in 100 people have it in Africa.
1 in 500 African Americans have it in the U.S.
Why?
Types of Selection
Balancing Selection (Stabilizing) – to
opposing forces affect the frequency of an
allele in a population.
Directional Selection – meaning a trait is
moved to one extreme end or the other.
Diverging Selection (Disruptive) – makes for
2 populations of extremes. Two opposite
traits are favored in different environments.
Types of Selection - Diagram
Species
Species – are groups of individuals that
when bred produce fertile offspring.
Are donkeys and horses of the same species?
Species can live in different
environments.
Over time as their different
environments change different traits
become better for survival.
Ecological Races
Populations of the same
species that differ
genetically because they
have adapted to different
environments.
Ex. Sparrow
Eventually with time they
will become different
species.
Meaning they will be unable
to breed anymore.
Evolutionary Speed Theories
Gradualism – The theory that evolution
occurs in a slow and constant speed.
Punctuated Equilibria – The theory that
evolution can only occur rapidly after major
environmental upheavals (Ex. Meteor
strikes, earthquakes, etc).
Short periods of rapid species formation along
with long periods where little evolution occurs.
EVIDENCE
For Darwin’s Theory
Evidence
There are 3 types of evidence to
support Darwin’s theory used today.
Fossils
Comparing physical structures
Biochemical Evidence
Fossils
A fossil is any trace of a dead organism.
Examples: Dinosaur skeletons and tracks, leaf
impressions, shells, and mosquitoes trapped
in tree sap.
Fossil Formation

The organism must be buried soon after death in
places such as the bottom of the ocean, in mud,
or tar pits.

The calcium will be replaced with harder
minerals.

If there is no oxygen present the tissue may still
be present. But, if any oxygen is present the skin
and tissue will decay away.
Fossil Dating
Scientists measure radioactive Beta
Decay of Carbon 14 into Nitrogen.


It takes 5, 730 years for half of Carbon 14 to
become Nitrogen.
So, if there is always a 1:1 ratio of regular
Carbon 12 to Carbon 14 while an organism is
alive, then they can measure the amount of
Carbon 12 to determine how much Carbon 14
must have been present at death.
Question…

If there was 24 grams of Carbon present right
before fossilization and now there is 12 grams
left how much time has passed?
Intermediate Fossils
If new species are adapted from other
organisms Darwin predicted that there
would be transitional, or intermediate,
forms of organisms in the fossil record.
Examples:
fish intermediates
Comparing Structures
Homologous Structures: are structures
that are similar in
form or shape.
Ex. Chimp hands, human
hands, and Tarsier hands all
have the same types of
bones.
Vestigal Structures
These are structures that have no
purpose today, but may show the
evolutionary past of the organism
because at one time they were
necessary.
Example: Whales
unnecessary pelvic bone.
Embryonic Patterns
Organisms that are
similar as embryos
may be more closely
related.
What is the reasoning
behind this thought?
DNA and Protein Evidence
Organisms that have similar DNA are
more closely related then organisms
with many nucleotide differences.
DNA differences mean more protein
differences.
Ex. A chimp Cytochrome C (protein) has the
exact same DNA sequence as the human
Cytochrome C.
Ex. A rattlesnake’s Cytochrome C has 20
differences in amino acids when compared to
us.