Download Unit Four

“Origin of Species”
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In 1831 Charles Darwin took a voyage around
South America on a ship, the HMS Beagle
He was the ship’s naturalist; He made many
observations about the flora and fauna during
the 5 year voyage
He kept a journal of his observations that he
revisited once he returned to Great Britain
In the years that followed his voyage he
formulated his ideas into several published
works that caused people to think more about
our origin as species
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Darwin published his ideas in a book entitled
…On the Origin of Species in the late 1850’s
He has since been credited with the theories of
evolution and natural selection
Darwin was not alone though. Alfred Wallace
independently asserted the same hypothesis as
Darwin in reference to natural selection
Wallace wrote a letter to Darwin in 1858
explaining natural selection based on his own
observations in nature; this prompted Darwin
to quickly publish his life’s work
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Evolution – change in the genetic composition
of a population due to chance alone
Natural Selection – the process by which more
favorable changes in the genetic composition
enhance survival and those less favorable
changes decrease survival
Adaptation – all individuals in a population
now possess those favorable changes, and
those changes are now the accepted physical
characteristics of the species
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The neck of a Giraffe
The speed of a Cheetah
The long snout of an Anteater
The white fur of a Snowshoe Hare
What is your example?
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Many people of faith object to the theory of
evolution: notion that our DNA is similar to
other species and we are related
Their objections are rooted in their
interpretation of sacred scripture
There are some faiths that do not object to the
theory of evolution because they believe it was
“ordained by God”
Why mention religion in a biology class…..it is
still a contested issue in the 2000’s
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the theory that the universe and living things were
designed and created by the purposeful action of an
intelligent agent
Research addressing alternate hypotheses to the
Theory of Evolution
“Intelligent Design” is an umbrella term used for any
scientific research investigating the origin of species,
the earth, and the universe
Intelligent Design is not Creationism
Creationism is a religious belief held by protestant
Christians that the earth is only several thousand years
old; they interpret sacred scripture literally
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Microevolution – small beneficial changes in
physical characteristics of a population that
slowly become dominant within the entire
population
Macroevolution – a physical change in an
entire population that causes that population to
be different from other populations of that
species; if the previous is the case the
“changed” population is now a new species
In essence, microevolution leads to
macroevolution
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Lamarck – the environment causes changes in
the species
Darwin – changes occur and are either
beneficial or detrimental in reference to the
environment
The variation that leads to some physical
characteristics being more adapted to the
environment is the result of genetic mutations
Recall that genetic mutations occur due to
chance alone
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The most compelling form of evidence
supporting the theory of evolution is the
presence of fossils
Fossils can be present in many forms:
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Fossil remains – bones (solid portions of organisms)
Trace Fossils – footprints or imprints
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Another type of evidence supporting the
theory of evolution is direct observation by
scientists of “Microevolution”
Microevolution can be observed in species that
reproduce often and have short lifespan
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Example: Drosophila melanogaster
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1. Assemble a set of fossils of a particular group
of organisms
2. Date each of the fossils by analyzing the rock
in which the fossils are held for the rock layers
approximate ages
3. Order the fossils by their age (age of rock in
which they were found)
4. Examine the fossils
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While there are still gaps in the fossil record,
clear connections do exist showing the
transition between all major groups of
vertebrates:
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fish to amphibians
amphibians to reptiles
reptiles to birds
birds to mammals
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Homologous Structures – a physical structure that
over time diverges in form and function
Homologous structures lead to “Divergent
Evolution”
Analogous Structures – physical structures that are
initially different in form and function but over
time converge to have a similar form and function
Analogous structures lead to “Convergent
Evolution”
Forelimbs of vertebrates (human versus horse)
 Wings of birds and bats (arm bones versus hand bones)
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Due to the mechanism of evolution, one should
observe the more distant the relatives, the less
similar their genomes will be
Conversely, the closer the evolutionary relatives,
the more similar their genomes will be
In reality, the genetic evidence supports the
previous statements, which in turn further
strengthens the theory of evolution
This same pattern of divergence as the
evolutionary relatives become less similar can also
be seen at the level of the protein
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Arguments advanced by Darwin’s Critics:
1. Evolution is not solidly demonstrated ….
Evolution is just a theory
 2. There are no fossil intermediates (in the 1800’s)
 3. The Intelligent Design argument - “The organs of
living creatures are too complex for a random
process to have produced.”
 4. Evolution violates the second law of
thermodynamics – “tendency of the universe toward
disorder”; what the law really states: “disorder
increases in a closed system”
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5. Proteins are too improbable
6. Natural Selection does not imply evolution
7. Life could not have evolved in water
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If the allele frequencies of a population are not
changing, then the population is not evolving
… this is “Hardy-Weinberg equilibrium”
There are many factors that can propel a
population out of Hardy-Weinberg
equilibrium:
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1. change in size of the population
2. immigration
3. genetic mutations
4. monogamous nonrandom matings
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In order for a species to remain extant genetic
diversity is very important
There are several factors that enhance genetic
diversity:
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1. many individuals of a species
2. many populations of a species
3. immigration and emigration
4. constant reproduction
5. minimal inbreeding
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Conservation geneticists use their knowledge
and understanding of DNA to increase genetic
diversity through breeding
They artificially control/manipulate which
individuals are able to breed in order to
encourage an increase in genetic diversity
As the endangered species total number and
variation in the gene pool increase, the
likelihood the species will survive increases
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Genetic Drift – random fluctuations in allele
frequencies in a small population over time
Founder Effect – the effect by which rare alleles
and combinations of alleles may be enhanced
in new populations ( an island)
Bottleneck Effect – a catastrophic event that
greatly reduces the size of a population thereby
greatly reducing the genetic variation of the
population
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Stabilizing Selection – extreme phenotypes are
eliminated (baby birth weight)
Disruptive Selection – the common
intermediate phenotype is eliminated and the
extreme phenotypes are preserved (finch beaks
are large and small)
Directional Selection – one extreme phenotype
is eliminated (minimal presence of
phototropism in fruit flies)
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Blood clotting disorder found in Americans of Central
African decent and in those people still residing in Central
Africa
It is a painful disorder that reduces the bloods ability to
carry oxygen due to the shape of the hemoglobin; the sickle
shape of the hemoglobin causes it to get caught in the tiny
capillaries of a person’s circulatory system thereby causing
extreme discomfort;
Someone with the disorder usually has a shortened lifespan
It does serve a purpose, especially in Central Africa: those
people with it are much less susceptible to Malaria, which is
often deadly
Homozygotes for sickle cell anemia die early in life,
Heterozygotes are resistant to Malaria, Homozygotes that
do not have sickle cell anemia will die if they contract
Malaria
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If there is no change in the environment, then
there is no need for physical changes in a
species
However, the only thing that stays the same is
that the environment changes
The abiotic changes in the environment make it
more likely for species mutations to be
demonstrated in the population
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A species is defined as those individuals that
can mate with each other and produce
offspring that are reproductively capable
themselves
Speciation is the process by which new species
develop from already existing species
How does speciation occur? (Darwin’s Finches)
Speciation occurs via “Isolating Mechanisms”