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Evolution
Chapter 16
Early Theory of Evolution
 Lamarck, a French biologist, proposed:
◦ That body structures could change according
to the actions of the organism.
◦ Acquired characteristics could be passed on
to any offspring.
◦ He was incorrect, but paved the way for
Darwin.
Developing the Modern Theory of
Evolution

@Charles Darwin published ideas on
how species evolved and they became the
basis of modern evolutionary theory@;
◦ He took a job as a naturalist on the HMS
Beagle where he traveled to South America
and the Galapagos Islands collecting samples
of specimens
◦ He made many observation and after further
experimentation he proposed the process of
natural selection.
Darwin’s observations:
Finches and tortoises had different beaks
and shells/necks depending on diet.
 However, all the finches and all the
tortoises have many similar physical
characteristics suggesting a common
ancestor for each.
 The differences in the finches and
tortoises was due to adaptation to the
food source.

Natural Selection

@Survival of the fittest, those individuals
better suited to survive@
◦ Darwin wrote “ On the Origin of Species by
means of Natural Selection”, after years of
observations and studying evidence he
collected on the mechanism of change.

4 principles of Natural Selection:

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Variation
Heritability
Overproduction
Reproductive advantage
Evolution
@Is cumulative changes in groups of
organisms through time.@
 Natural selection is not evolution but it is
the mechanism by which it occurs.

5 Types of Evidences of Evolution
1.
Fossils - Recorded for Earth’s history.
5 Types of Evidences of Evolution
2.
Anatomy
 Homologous structures – Similar
structures, Different use or function.
 Analogous structures – different structure
but are similar in function.
 Vestigial structures – a body part structure
that has no function in a present day organism
but was useful to an ancestor. (ex human appendix)
5 Types of Evidences of Evolution
3.
Chemistry – reveals relationships
between organisms, species, and
individuals.
◦ Using RNA and DNA.
5 Types of Evidences of Evolution
4.
Embryology – through development of a
tail and gill silts can be seen in embryos
of birds, reptiles, and mammals.
5 Types of Evidences of Evolution
5.
Distribution – geographical distribution
Extra Credit Question
What is this fish’s name and
what TV show is it from?
Blinky. The Simpsons
Adaptation

@A trait shaped by natural selection that
increases an organisms reproductive
success.@
 Mimicry – is a structural adaptation that enables
one species to resemble another; predator may
avoid them if they look harmful.
 Camouflage – an adaptation that enables species
to blend with their surroundings.
Population Genetics
Populations evolve not individuals.
 Natural selection acts on poor
phenotypes that will not benefit the
survival of the organism.
 Genes in the population are called gene
pool.

5 Mechanisms of Evolution
5 Mechanisms of Evolution
1.
Genetic drift – change in frequency of
gene variations in a population.
 Founder’s effect reduction in alleles resulting
from a small group settling in a separate location
away from the rest of the population.
 Bottleneck effect is a reduction in alleles
resulting from a chance event that drastically
decreases population size.
5 Mechanisms of Evolution
2.
Genetic flow – migrating individuals
transport genes.
5 Mechanisms of Evolution
3.
Non-random mating – organism
mate with individuals in close proximity.
4.
Mutation – change in genetic material.
Extra Credit Quote
Mutation, it is the key to our evolution. It
has enabled us to evolve from a singlecelled organism into the dominant species
on the planet. This process is slow, and
normally taking thousands and thousands of
years. But every few hundred millennia,
evolution leaps forward.
–Professor X (X-Men 1)
Or
-Dr. Jean Gray (X-Men 2)
5 Mechanisms of Evolution
5. Natural
Selection acts on variation –
“Survival of the fittest”
 Types of Natural selection
◦ Stabilizing selection – favors average individuals.
◦ Directional selection – favors one extreme or
the other, example very large or very small.
◦ Disruptive selection – favors individuals of both
extremes.
◦ Sexual selection – changes in
frequencies of traits based on
ability to attract mates.
Speciation

Speciation – evolution of new species.
 Allopatric speciation – physical barrier divides a
population into 2 or more population.
 Sympatric Speciation – a species evolves into a
new species without physical barriers.

Reproductive isolation occurs when
formerly interbreeding organisms can no
longer mate and produce fertile offspring.
◦ Prezygotic isolation – prevent fertilization
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Geography
Behavioral
Mating time
Physical differences
◦ Postzygotic isolation – when fertilization
occurs, prevent hybrid organism from
reproducing. (sterility)
Patterns of Evolution

Adaptive radiation (Divergent evolution) –
when ancestral species evolve into an array
of species to fit number of diverse habitats.
◦ patterns in which similar species become
increasingly different.
Patterns of Evolution

Convergent evolution – patterns of
evolution in which distantly related
organisms evolve similar traits.
 Due similar environmental pressures.
Rate of Speciation
Gradualism is the idea of
that species originating
through a gradual change of
adaptation.
Punctuated equilibrium is
rapid speciation, in burst with
long periods of genetic
equilibrium in between.