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Chapter 15 & 16
Theory of Evolution
Population Genetics and
Speciation
History of Evolution
I. Evolution – is the theory that species
change over time.
II. Theory of evolution before Darwin – Jean
Baptiste de Lamarck
Inherited characteristics not in use will
disappear. No evidence or experiences to
support.
Jean Baptiste De Lamarck
Charles Darwin
III. Charles Darwin (1809-1882)
Failure in school.
Studied to be a doctor
Studied to be a clergy
Became naturalist on the HMS Beagle – a
5 year mapping and collecting expedition
to South American and the South Pacific
Observed changes in land – if habitats
changed animals would have to adapt.
Giant Tortoise
Blue Footed Booby
Blue Feet
Galapagos Islands Map
Studied fossils – compared homologous
structures- similar structure with possibly
different function and Vestigial Organsstructure that works in one species, but
does not function in other.
Example: appendix.
Fossils of similar species should be more
similar in the past – fossil records.
What is a species?
IV. What is a species? Species comes from
the Latin meaning kind or appearance.
**Species members can reproduce and
produce fertile offspring.
V. Species classified by:
1. Morphology – similarities and differences
in internal and external structures.
Includes biochemistry- actual
chemical make up and embryonic
development- development in womb
between similar species more closely
related. Some members of the same
species may not look alike. Ex: Flicker – 2
morphologically different parents produce
hybrid. All the same species just different
appearance.
2. Classification expanded to include
reproductive capability. If an organism is
classified solely on breeding capability it is
classified by the Biological Species
Concept (BSC).
3. Using both Morphology and BSC can
explain how species change.
VI. What is a population?
1. The number of a species in a specific area
at a specific time
2. Scientist study variation in population
Genotype/Phenotype
3. Collection of genes of a population is its
gene pool.
4. Gene pool contains all possible alleles for all
genes.
5. Allele frequency = % of specific allele of a
gene in gene pool.
6. If allele frequency does not
change from generation to
generation = genetic equilibrium.
Population will look the same
generation to generation.
VII. Conditions for genetic equilibrium:
1. No mutations 2. No migrations 3. Large
populations 4. Mate randomly 5. Natural
selection doesn’t occur
If conditions change genetic equilibrium,
evolutionary change or change in species
may occur.
VIII. The conditions for genetic equilibrium
were outlined by Godfrey Hardy (British
Mathematician) and Wilhelm Weinberg
(German Physician) = Hardy Weinberg
Principle
IX. Types of change:
1. Mutation – is a physical change in the
gene or chromosome
2. Migration – changes allele frequency,
disrupts genetic equilibrium
3. Gene flow – movement of genes in or out
of a population.
4. Genetic drift – allele frequencies change
as a result of random events, significant in
small & medium populations.
• X. Thomas Malthus – Essay on the
principal of population stated that:
Population will double every 25 years.
• Natural resources do not increase at same
rate. Struggle for existence becomes
struggle for resources
XI. Natural Selection
XI. Natural Selection – most advantageous
variations most likely to survive and
reproduce
1. Inherited variation could change a
species or can create a whole new
species – process called speciation.
2. Adaptive radiation – changes forming
related species to adapt to different
habitats and reduce competitions
3. Divergent evolution- related species
becomes more and more dissimilar.
4. Convergent evolution- an unrelated
species becomes more and more similar.
5. Coevolution- 2 or more species through
interactions develop a specialization for
other.
Example: predator/prey
provider/host (parasite)
flowers/insects
Convergent Examples
Peppered Moth
XII. Natural selection does occur:
1. Stabilizing selection – average is best –
bell curve
2. Directional selection – one extreme or
the other is best.
3. Disruptive selection – either extreme is
advantage
4. Sexual selection – preferred choice of
mate