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Early Evolutionary
Theory
Where did the Theory of
Evolution Come From?
Jean-Baptiste Lamarck
(1744-1829)
 Created
an incorrect Theory of
Evolution based on the inheritance
of Acquired Characteristics
Lamarck Incorrectly
Believed…

Giraffes originally had short necks & since
food was scarce, they reached for leaves in tall
trees. This caused their necks to
stretch. Offspring inherited this
trait.

Special use of a body part does not change the
genetic make-up of that part!
Charles Darwin
(1809 – 1882)
 “Father
of Evolution”

Voyaged to the
Galapagos Islands on
H.M.S. Beagle (18311836) as the ship’s
naturalist.

Recognized that
populations respond
(over many
generations) to changes
in their environments.

Example: Finches
The finches he studied had differently
shaped beaks depending on where they
lived and what they ate.
Who is Charles
Darwin?
 Video
 Jot
Clip!
down some key points about
Darwin and his discoveries!
Alfred Russell Wallace

Was also voyaging and
observing similar things to
Darwin.

Sent an essay to Darwin
that did not use the term
“natural selection” but
described the same ideas.

Darwin published their
ideas in a paper on the
theory of evolution.
Natural Selection
 Conditions
in nature determine
which organisms survive and
reproduce (a process that leads
to evolutionary change)
4
components of natural
selection…

1. Variation – individuals in populations
differ from one another.

2. Heritability – Variations are inherited from
parents.

3. Overproduction: Populations produce
more offspring than can survive. May
result in competition between offspring for
resources.

4. Reproductive Advantage – Variations
that increase reproductive success will be
more common in the next generation.
Example: Porcupines evolved to have quills
because they help to avoid predators and therefore
reproduce.
Natural Selection
results in only some
individuals surviving…
Survival of the Fittest!
(fitness – not necessarily the
strongest…the fittest individuals
leave the most offspring)
What do you think will happen over time to
this beetle population?
What leads to
variation among
species?
Mechanisms of Evolution
 1.
Mutations
 2. Genetic Drift
 3. Gene Flow/Migration
 4. Natural Selection
1. Mutations
 Changes
in DNA sequences that
can result from environmental
factors (chemical exposure/
radiation) or simply by chance
Mutation Cont’d…

Can lead to no change in phenotype
 When
the mutation occurs on a stretch of
DNA that does not code for anything

Can lead to small changes in phenotype
 When

cat’s ear has a slight curl
Can lead to big changes in phenotype
 Death
Gene Pool
A
collection of genes for all the traits
in a population
 If
gene mutations persist, they may become a
standard part of that population.
2. Genetic Drift

Affects the genetic make-up of a population
through an entirely random process

“Lucky” individuals survive, not necessarily the
healthier or more “fit” individuals.

May decrease genetic
diversity!
3. Gene Flow
 Also
called Migration
 Movement
of individuals into or out
of a population (variations are
distributed among the populations)

Examples: People moving to a new city
Reasons for Migration

Overcrowding of organisms in one area

Lack of food/water

Reproduction

Ex. Male lions migrate before reaching maturity. If
the lion leaves, it’s genetic make-up will be lost
from its population, but will be added to a new
population.
4. Natural Selection
 Conditions
in nature determine
which organisms survive and
reproduce.
 Necessary
if genes are to stay in a
population
Speciation
How do new species
emerge?
Species
A
group of organisms that breed
with one another and produce
fertile offspring
Geographic Isolation
 When
a natural, physical barrier
separates a population and they
evolve separately from each other
 Physical
barriers: body of water,
landslides, mountains, deserts, etc.
Cont’d…

Without the flow of genes, the separated
species differentiate (change) to enable them
to survive in their environments.

Ex:
Reproductive Isolation
 The
inability of formerly
interbreeding organisms to produce
offspring
 Ex.
Ringed Salamander of California
*
Geographic
Isolation can
lead to
Reproductive
Isolation
Ex: Wood frog & Leopard frog

In captivity, they will breed, but in the wild they
will not because of different breeding seasons
Wood frog – early April
 Leopard frog – mid April

Their species diverged because
they did not breed at the same
time.

Population Bottleneck
 Occurs
when a population’s size is
reduced for at least one generation.

Northern elephant seals have reduced genetic
variation probably because of a population
bottleneck humans inflicted on them in the
1890s. Hunting reduced their population size
to as few as 20 individuals at the end of the
19th century. Their population has since
rebounded to over 30,000—but their genes
still carry the marks of this bottleneck: they
have much less genetic variation than a
population of southern elephant seals that was
not so intensely hunted.
Killer Whale
Article
February 4, 2014
1.
2.
3.
4.
5.
Describe what is meant by “upwelling system.”
What is believed to have caused a genetic
bottleneck in whale populations? Why?
Why did the population of killer whales off the
coast of South Africa retain it’s genetic
diversity?
Why was hunting ruled out as an effect on the
bottleneck in populations?
What additional evidence does the author
suggest, could be used to support the claim that
reduced genetic variation is a result of the last
glacial period?