EVOLUTION AND NATURAL
SELECTION
Change over time…
GEOLOGY
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Began to study rock layers called
strata
 George
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Cuvier
Studied fossils
Found extinct species and
noticed the deeper the fossil
the more unique
Catastrophism
 Charles
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Lyell
Believed the earth to be
millions of years old
Uniformitarianism
JEAN BAPTISTE LAMARCK
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In 1809, Lamarck proposed
that organisms evolved into
more and more complex
forms through use and
disuse and the inheritance of
acquired characteristics
Organism strived to improve,
causing new body structures
to develop and “unused”
structures to disappear
Used structures would pass
on to the offspring
This theory is NOT accepted
today
CHARLES DARWIN AND THE BEAGLE
In 1831, at the young age
of 21, Charles Darwin
took a job as a naturalist
on the British ship know
as the H.M.S. Beagle
 On his five year journey
Darwin studied and
collected many different
organisms
 When Darwin arrived at
the Galapagos Islands, he
was intrigued by the odd
variety of species he saw
there
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THE GALAPAGOS ISLANDS
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This small group of islands
is home to many unique
creatures, such as the giant
tortoise, large marine
iguanas, and flightless birds
know as the cormorant
In particular, Darwin
noticed that there were
many varieties of finches.
Each variety was similar to
the finches of the mainland
of South America, yet
adapted to its environment
in a unique way.
ADAPTATION – Any
inherited characteristic or
behavior that helps an
organism better survive in
its environment
THE ORIGIN OF SPECIES
When Darwin returned to
England, he took his
findings and compiled them
into a book. It was not until
another scientist, Alfred
Wallace, approached him
with his findings of how
evolution worked that
Darwin would publish his
work.
 In 1859, Darwin published
The Origins of Species, By
Means of Natural Selection
 He stated that evolution
occurred through natural
selection.
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NATURAL SELECTION

Darwin proposed that natural
selection caused species to
change
1)
2)
3)
4)
Overproduction Organisms produce more
offspring than can survive,
Genetic Variation - There is
variation
Struggle to Survive - Some
variations help the organism
survive better in its
environment. (Competition
over food, mates, shelter,
water, etc.)
Differential Reproduction
– Individuals with the best
traits reproduce more. Over
time more individuals will
have the favored trait.
Therefore, the population
gradually changes, evolves,
over time to better suit its
environment.
Survival of the fittest
Fitness is a measure of an
individual’s hereditary
contribution to the next
generation.
ADAPTATIONS
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Fitness- a measure of
an organisms
contribution of viable
offspring to the next
generation
Camouflage –
adaptation that allows
for blending in with the
environment
Mimicry – one species
evolves to look like
another species
Antimicrobial resistance
– “Super” bacteria;
bacteria that are
resistant to most
antibiotics
DO NOW
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Who is Lamarck? What did he do?
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What is an adaptation?
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Lamarck was one of the first scientist to proposed evolution. He
believe that traits could be acquired throughout a life time and
passed on to offspring. Anything that an organism did not use
during that lifetime would be lost, hence his theory of acquired
characteristics through use and disuse.
Any inherited characteristic or behavior that helps an organism
better survive in its environment
What are the 4 aspects of natural selection?
Over reproduction
Variation among the species
A struggle for survival – some are better suited than others and
will survive to reproduce
 Inheritable traits meaning that the more favorable traits are
passed on and begin to become a larger portion of the
population
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EVIDENCE FOR EVOLUTION
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Darwin’s theory is
supported by many
different types of scientific
evidence
Fossils clearly show that
many species have
changed over time; some
fossils show transitional
forms (intermediate
species between old and
new species)
Derived v. Ancestral
Traits
New traits v. old
 Feathers v. teeth
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EVIDENCE FOR EVOLUTION - STRUCTURES
Homologous structures
– many species with
common ancestry show
similar structures. Ex:
forelimbs have similar
bone structure
 Analogous Structures –
unrelated species living in
similar habitats often
have similar structures.
Ex: shark and dolphin
fins/ bird and insect wings
 Vestigial Structures – a
structure that no longer
serves a purpose. Ex:
appendix (humans) or
pelvic bone (whales)
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COMPARATIVE EMBRYOLOGY AND GENETICS AND BIOGEOGRAPHY
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Genetic evidence –
today, similarities in
DNA and amino acid
sequences show how
species are related. Ex:
humans and
chimpanzees (our closest
living relative) share
over 90% of our DNA
Embryology –
vertebrates share similar
characteristics at early
stages of development
Biogeography – the
distribution of plants
and animals effects how
natural selection works
on them
PATTERNS OF EVOLUTION
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Isolation and natural selection can
lead to different types of evolution
Convergent evolution – distantly
related organisms become more
similar over time due to similar
habitats
Divergent evolution – one species
eventually diverges into two or more
species, becoming increasingly
different over time in response to
different environments
 Adaptive radiation
Artificial Selection – Humans choose
the traits that they want which leads
to evolution as well
Coevolution – when two interacting
species evolve around each other
(predator/prey; host/virus;
plant/pollinator)
ISOLATION
Speciation often begins when
two groups become isolated
 Two types of isolation
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Geographic isolation – a
physical barrier separates 2
groups, such as a body of water,
mountain range, highway etc.
 Reproductive isolation –
occurs when 2 groups cannot
reproduce together; sometimes
caused by geographic isolation,
but can also occur because of a
change in behavior
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Prezygotic isolation
 Postzygotic isolation
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SPECIES
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The process of species formation
is called speciation.
For many years species were
determined by morphology,
the internal and external
appearance of an organism.
The morphological concept of
species has limitations since
individuals within a species can
look different.
The biological species
concept says that a species is a
population that can interbreed
but cannot breed with other
groups.
Modern day definition states
that a species is one that looks
similar and allows for
interbreeding to produce fertile
offspring
NON-RANDOM MATINGS
Stabilizing selection is when the individuals
with the average form of the trait have the
highest fitness.
 Directional selection is when the
individuals with a more extreme form of the
trait have greater fitness than the average form
of the trait.
 Disruptive selection is when the individuals
with either form of the extreme trait have
greater fitness than the average form of the
trait.
 Sexual selection is when one mate has to
chose the other based on certain
characteristics.
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BIODIVERSITY
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Evolution usually leads
increased biodiversity
Increased biodiversity
strengthens an ecosystem by
increasing the “connections” in
the food web and making it less
susceptible to disease
If species cannot evolve quickly
enough, evolution may lead to
extinction
There have been 5 mass
extinctions throughout history
Are humans currently causing
the next mass extinction?