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Theory of Evolution
What is evolution?
A change over time;
a change in species over time.
Who was Jean-Baptiste
de Lamarck?
A French naturalist who was the
first to recognize evolution.
• He said things change
over time.
• He believed that
organisms change
because of an “inborn”
will to change.
• He believed that
organisms could change
their body structure by
using or not using body
parts
• Lamarck was incorrect.
Who was Charles Darwin?
A British naturalist who developed
the current theory of evolution by
natural selection.
• He traveled for 5
years on the HMS
Beagle to South
America, the
Galapagos Islands
and South Pacific
• Darwin wrote the
Origin of Species, in
which he presented a
lot of evidence to
support his ideas of
evolution.
Who was Alfred Russel Wallace?
A naturalist who gave Darwin his paper on
natural selection. They presented their
papers together at a scientific meeting.
How Are We Doing?
Who thought that an organism could ‘want’
something enough to evolve?
Wallace or Lamarck.
Who was the first to ‘write’ about natural
selection?
Darwin or Wallace.
What is Natural Selection?
A mechanism for change in
populations.
• it occurs when
individuals with more
favorable variations
for a particular
environment survive
and pass on these
traits
• those without
favorable variations
are ‘selected’ to die
What are the major points
of natural selection?
1. Variations (differences among
individuals of a species) exist
within populations.
2. Some variations are more
advantageous (adaptations)
3. Organisms produce more
offspring than can survive.
4. Over time offspring of survivors
will make up larger proportions of the
population as those selected for death
disappear.
How Are We Doing?
List two of the parts of the natural selection
mechanism.
Why does natural selection suggest one
organism dies instead of another?
Adaptations better for the environment or a
random dying individual.
Artificial Selection
• Nature provided the variation, and humans
selected those variations that they found
useful.
Adaptation
• Any inherited characteristic that increases
an organisms chance of survival.
• Individuals that are better suited to their
environment survive and reproduce most
successfully. Known as Survival of the
Fittest.
Principle of Common Descent
• All species living and extinct were derived
from common ancestors.
What are some of the
supporting data for evolution?
1. Fossils
• They are remains or traces of organisms
that lived long ago.
2. Anatomy
• Comparing body structures
of living organisms.
• Homologous Structures:
structures in different
species that have the same
evolutionary origin.
• Vestigial organs- small or
incomplete organs that
have no apparent function.
3. Embryo Development
• Early stages in the development of some
organisms also provide evidence of common
ancestry.
4. Chemical Evidence (DNA)
• By studying the sequence of amino acids in
proteins we can see how closely related
certain species are to each other.
How are we doing?
List 2 types of evidence
supporting evolution.
Gene Pool
• Consists of all the genes, including all the
different alleles that are present in a
population.
Section 16-1
Figure 16–2 Relative
Frequencies of Alleles
Sample Population
48%
heterozygous
black
16%
homozygous
black
36%
homozygous
brown
Frequency of Alleles
allele for
brown fur
allele
for
black
fur
Single Gene and Polygenic Traits
• Single gene trait- controlled by single gene
with two alleles.
• Polygenic traits-controlled by two or more
genes and alleles. Results in many different
phenotypes and genotypes.
Section 16-1
Figure 16–3 Phenotypes for
Single-Gene Trait
100
Frequency of Phenotype
(%)
80
60
40
20
0
Widow’s peak
Phenotype
No widow’s peak
Generic Bell Curve for
Polygenic Trait
Frequency of Phenotype
Section 16-1
Phenotype (height)
Directional Selection
• Individuals at one end of the curve have
higher fitness than individuals in the middle
or at the other end.
Section 16-2
Figure 16–6 Graph of
Directional Selection
Key
Directional
Selection
Food becomes scarce.
Low mortality,
high fitness
High
mortality, low
fitness
Stabilizing Selection
• When individuals near the center of the
curve have a higher fitness than individuals
at either end of the curve.
Section 16-2
Figure 16–7 Graph of
Stabilizing Selection
Stabilizing Selection
Key
Low mortality,
high fitness
High
mortality, low
fitness
Birth Weight
Selection
against both
extremes keep
curve narrow
and in same
place.
Disruptive Selection
• Individuals at the upper and lower ends of
the curve have higher fitness than
individuals near the middle.
Section 16-2
Figure 16–8 Graph of
Disruptive Selection
Disruptive Selection
Low mortality,
high fitness
High mortality,
low fitness
Population splits
into two
subgroups
specializing in
different seeds.
Beak Size
Number of Birds
in Population
Key
Number of Birds
in Population
Largest and smallest seeds become more common.
Beak Size
What affects speciation?
(formation of a new species)
When two groups in a population become
isolated from each other.
1. Geographical isolation:
• When a physical barrier cuts a single breeding
population in two
2. Reproductive isolation:
When a barrier to interbreeding caused by varied
breeding times.
How Are We Doing?
Reproductive and geographical __________
affects speciation.
Does speciation take place rapidly?
Yep or Nope.
Distinguish between the process of
adaptive radiation and convergent
evolution (adaptive convergence)
1. Adaptive radiation
• A type of
evolution of
many diverse
species
deriving from a
single,
ancestral
species.
2. Convergent Evolution
(Adaptive convergence)
• A type of
evolution in
which
unrelated
species
produce
descendents
with similar
traits.
How fast does evolution occur?
1. Gradualism
• Showing a steady,
slow and continuous
change of one
species into new
species.
2. Punctuated equilibrium
• The process that
shows the rapid
change of a species
caused by the
mutation of just a
few genes.
Gradualism vs. Punctuated
Equilibrium
How Are We Doing?
What are the two models describing how long
evolution takes?
Gradualism/Punctuated Equilibrium or
Adaptive/Convergent Radiation.
Does evolution take a long time?
Yes or No.
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