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Darwin not first to suggest evolution occurs. Jean Baptiste Lamarck (1744-1829). Published his theory of evolution in 1809. Mechanism -- Inheritance of acquired characteristics. Inheritance of acquired characteristics: Characteristics an organism acquires
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Jean Baptiste Lamarck (1744-1829).
Published his theory of evolution in
Mechanism -- Inheritance of acquired
Characteristics an organism acquires
during its lifetime are passed on to
Example: Giraffes stretch their necks to
reach leaves. As a result their young
born with longer necks.
because DNA is not changed by an
organism’s behavior or experiences.
One-way flow of information from
DNA to body.
Son of a wealthy doctor.
Studied medicine. Dropped out.
Then studied theology.
Keen naturalist and hunter.
Darwin companion for Captain Fitzroy.
(Darwin not the official naturalist.)
Beagle sailed around the World.
Mission to map coast of South America.
Volcanic islands (hence of recent origin)
off coast of Ecuador.
Unique animals on Galapagos include
giant tortoises, marine iguanas, and
Principles of Geology.
1. Gradualism: Geological features can be explained by gradual action of processes we see around us. E.g. wind, waves, rivers.
2. Great age of the earth
1. South American fossils resembled
e.g. Extinct glyptodont (2,000 kg)
resembles modern-day armadillo (2 kg).
2. Parts of the world with similar
climates (e.g. Australia, South America)
populated by very different organisms.
3. Plants and animals on each continent
E.g. kangaroos in Australia, guinea pigs,
armadillos in South America.
4. Many species on oceanic islands are
found only there (endemic).
Often groups of very similar species
found on these islands.
E.g. Galapagos finches and tortoises.
These are examples of adaptive radiation.
5. Endemic species on islands closely
resemble species on adjacent mainland.
that species are not unchanging.
Instead species change over time i.e.,
But how does evolution take place?
Malthus’s Essay on the Principle of
Malthus: Populations increase
geometrically (multiplicatively), but
resources do not.
Populations will outgrow their food
Darwin concluded that among organisms there is a struggle for existence. Only the best adapted organisms survive to breed.
Darwin called the mechanism that causes evolution to occur: natural selection.
5 observations and 3 inferences
Observation 1. If all organisms bred successfully populations would increase exponentially.
Observation 2. However, populations generally stay stable over time.
Observation 3. Resources are limited.
Because resources are limited, more
individuals are born than the
environment can support.
There is a struggle for existence (and
ultimately for reproduction.)
Only some individuals survive to breed.
their characteristics. There is variation.
Observation 5. Much of that variation
are not random. The characteristics of
an organism, which it inherits, affect
its chances of survival and reproduction.
Organisms best adapted to the
environment on average leave the most
heritable, differences between
individuals in their reproductive success
lead to changes in the characteristics of
the next generation. Evolution occurs.
did not publish them immediately.
In 1858 Alfred Russel Wallace wrote
to Darwin. He had independently
developed the theory of evolution by
Darwin published On the Origin of
Species in 1859.
Explained in detail his ideas about
evolution and natural selection.
he did not understand how inheritance
Darwin did not express his ideas in terms
of genes. He had no idea what genes
were or what DNA was.
DNA is the genetic material. The
instructions for making and “operating”
an organism are written in DNA.
DNA is divided into sections called
Together the genes determine the
characteristics of an organism.
If a single gene codes for flower
color, white and blue flowers would
be coded for by 2 different alleles.
One copy is inherited from each parent.
For a given gene you may have two
different alleles or two copies of the same
(* excluding genes on sex chromosomes
copies of a particular allele. (AA)
A heterozygous individual has two
different alleles. (Aa)
terms of genes because genes are the
only things passed from one generation
to the next.
that help organisms to survive
and reproduce become more common.
Genes that help less or are harmful
gradually are eliminated from the
most successful, e.g. the fastest, the best
camouflaged, the best foragers, etc.
succeed in breeding.
The genes of other individuals are not
passed on to the next generation.
describe the process by which the
best genes are chosen in each
Evolution occurs when gene frequencies
change from one generation to the next.
become increasingly well adapted to
Adaptations are characteristics of
organisms that enable them to survive
in their environments.
individual does not evolve.
Peppered moth occurs in two forms: light, speckled form and dark (melanic) form.
In early 1800’s dark form very rare.
Dark form caused by dominant mutation
that occurs spontaneously.
Dominant allele is expressed even if only
one copy is present. (i.e., is expressed
even in heterozygotes).
on camouflage for protection.
in lichens. Light form of moth hard for
birds to see.
In mid 1800’s air pollution in British
cities covered trees in soot.
In cities dark form of moth
became common and light form rare.
reduced air pollution in Britain.
Frequency of dark form has
declined steadily since then.
Peter and Rosemary Grant of Princeton
have studied Medium Ground Finches
on Daphne Major for almost 30 years.
Banded and measured the island’s
entire population and followed it over
In wet years lots of seeds produced.
In dry years few or no seeds produced.
seeds and small seeds.
Finches with smaller bills cannot eat
large seeds, but are more efficient at
eating small seeds.
for large bills) survive better than
small-billed finches (and genes for small
Mean beak depth of the finch population
fluctuates in synchrony with climate.
Sickle cell anemia is a condition common
in West Africans (and African Americans of West African ancestry).
In sickle cell anemia red blood cells are
Usually fatal by about age 10.
A single mutation causes a valine
amino acid to replace a glutamine
in an alpha chain of the hemoglobin
Mutation causes molecules to stick
eliminated by natural selection?
sickle cell gene get sickle cell anemia.
Individuals with one copy of sickle cell gene
(heterozygotes) get sickle cell trait
(mild form of disease).
Individuals with sickle cell trait don’t
Allele have higher survival than
either homozygote. Heterozygote advantage.
Sickle cell homozygotes die of sickle
“Normal” homozygotes more likely
to die of malaria.
Stabilizing selection for sickle cell allele.