The Theory of Evolution

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The Theory of
Evolution
Chapter 13 – Sect. 1: Natural
Selection
Charles Darwin - 1859
 Published convincing
evidence that
species evolve
 Proposed a
reasonable
mechanism to
explain how
evolution occurs
Darwin’s Voyage on the
HMS Beagle
Darwin’s Voyage on the
HMS Beagle
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
1831-1836 (5 year voyage)
Darwin was 22 years old at the start
Naturalist – someone who studies nature
Ships purpose was to survey the coast of
South America
Darwin’s Finches
Darwin observed that many
of the plants and animals
of the Galapagos Islands
resembled but were not
the same as those on the
nearby coast of South
America
Population – all the individuals of a species that live
in a specific geographical area and that can interbreed
Natural Selection
 Individuals that have physical or
behavioral traits that better suit their
environment are more likely to survive
and will reproduce more successfully
than those that do not have such traits
 These advantageous traits are adaptations
 As a result, the nature of the population
will gradually change – evolution!
Harsh Criticism
 Darwin wrote down his ideas about
evolution and natural selection in 1844
 He did not try to publish his work until
1858
 The theory of evolution goes against
religious beliefs and was not accepted by
the public in general
On the Origin of Species
published in 1859 (pg. 280 1-4)
 Inherited variation exists within the genes of
every population or species (the result of
random mutation or translation errors)
 In a particular environment, some individuals
of a population or species are better suited to
survive and have more offspring
 Over time, the traits that make certain
individuals of a population able to survive and
reproduce tend to spread in that population
 There is overwhelming evidence from fossils
and many other sources that living species
evolved from organisms that are extinct
Reproductive Isolation
 Two populations of the same species do not
breed with one another because of geographic
separation, a difference in mating periods, or
other barrier to reproduction
 These isolated populations will become more
different over time until they are no longer able
to breed with one another
The Tempo of Evolution
The Theory of
Evolution
Chapter 13 – Sect. 2: Evidence of
Evolution
Most Scientists Agree on
the Following:
 Earth is about 4.5 billion years old.
 Organisms inhabited Earth for most of its
history.
 All organisms living today share common
ancestry with earlier, simpler life forms.
The Fossil Record
 The preserved or
mineralized remains or
imprint of an organism
that lived long ago.
 Provide a record of
Earth’s past life forms
 Evidence of evolution
can be seen in the fossil
record.
Formation of Fossils
 The fossil record is not complete.
 Fossils do not form in all environments
 Most fossils form when organisms are
rapidly buried in fine sediments
 Bodies may decay too quickly or be eaten or
scattered
 Fossils are most likely to form in:
 Wet lowlands, slow-moving streams, lakes,
shallow seas, and areas near active volcanoes
Anatomy & Development
 Comparisons of the anatomy of different
types of organisms reveal basic
similarities in body structures
 The structures may have different functions
in different organisms
 Ex.) bones may be present in both organisms but
are reduced in size and have no use or less
important function
Vestigial Structures
 Reduced in size or
function, but may
have been complete
in an ancestor
 Ex.) hind limbs of
whales
Homologous Structures
 Structures that share
a common ancestry
 ex.) forelimbs of
vertebrates
Changes in DNA
 Mutation – a change in the nucleotidebase sequence of a gene or DNA
molecule
 If species have changed over time, then the
genes that determine the species’
characteristics should also have changed by
mutation
The Theory of
Evolution
Chapter 13 – Sect. 3: Examples of
Evolution
Natural Selection at Work
 Environment dictates
the direction and
amount of change in
evolution
 If the environment
changes in the future,
the set of
characteristics that
most help an
individual reproduce
successfully may
change
Factors in Natural Selection
(pg. 288 1-4)
 All populations have genetic variations.
 The environment presents challenges to
successful reproduction.
 Individuals tend to produce more offspring than
the environment can support.
 Individuals that are better able to cope with the
challenges presented by their environment
tend to leave more offspring.
Examples of Natural Selection
 Strains of lung disease tuberculosis (TB)
becoming resistant to certain antibiotics
 DNA in each strain is different = evolution &
natural selection
 Darwin’s finches developed different size
and shape beaks based on food sources
 Finches with proper beak for food survive =
evolution & natural selection
Formation of New Species
 Divergence – accumulation of differences
between groups
 Leads to the formation of new species
 Subspecies – populations of the same species
that differ genetically because of adaptations to
different living conditions
 Can become so different that can no longer
interbreed successfully
 Speciation – the process by which new species
form

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