Transcript Darwin, an English naturalist, proposed natural selection as the

DARWIN’S THEORY AND THE MODERN
SYNTHESIS
Darwin, an English naturalist, proposed natural
selection as the mechanism of evolution
• Darwin observed that
–organisms produce more offspring than
the environment can support
–organisms vary in many characteristics
–these variations can be inherited
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• Darwin concluded that individuals best
suited for a particular environment are more
likely to survive and reproduce than those
less well adapted
• Darwin saw natural selection as the basic
mechanism of evolution
–As a result, the proportion of individuals
with favorable characteristics increases
–Populations gradually change in response
to the environment
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• Darwin also saw that when
humans choose organisms
with specific characteristics
as breeding stock, they are
performing the role of the
environment
–This is called artificial
selection
–Example of artificial
selection in plants: five
vegetables derived from
wild mustard
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Figure 13.4A
– Example of artificial selection in animals: dog
breeding
German shepherd
Yorkshire terrier
English springer
spaniel
Mini-dachshund
Golden retriever
Hundreds to
thousands of years
of breeding
(artificial selection)
Ancestral dog
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Figure 13.4B
• These five canine species evolved from a single
common ancestor species through natural
selection
African wild
dog
Coyote
Fox
Wolf
Jackal
Thousands to
millions of years
of natural selection
Ancestral canine
Figure 13.4C
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Important terminology
• Variation – Having genotypic and phenotypic
differences in any population
• Heritable – Any genetics that can be passed on
to future generations
• Fitness – Success of an organism’s individual
adaptations and natural selection – usually
measured by ability to reproduce.
• Adaptation –traits that make an organism to
thrive and reproduce in its environment.
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4 parts of Natural Selection
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Scientists can observe natural selection in action
• Evolutionary adaptations have been observed in
populations of birds, insects, and many other
organisms
–Example: camouflage adaptations of mantids
that live in different environments
Figure 13.5A
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• The evolution of insecticide resistance is an
example of natural selection in action
Insecticide
application
Chromosome with gene
conferring resistance
to insecticide
Additional
applications of the
same insecticide will
be less effective, and
the frequency of
resistant insects in
the population
will grow
Survivor
Figure 13.5B
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Sometimes, natural viruses or bacteria attack a
population, killing those that have
susceptibility to disease, leaving only that that
are resistant to survive and reproduce.
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Populations are the units of evolution
• A species is a group of populations whose
individuals can interbreed and produce fertile
offspring
– Human populations tend
to concentrate locally, as
this satellite photograph
of North America shows
• The modern synthesis
connects Darwin’s theory
of natural selection with
population genetics
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Figure 13.6
Adaptive change results when natural selection
upsets genetic equilibrium
• Natural selection results in the accumulation of
traits that adapt a population to its environment
– If the environment should change, natural
selection would favor traits adapted to the
new conditions
• Because of this, it is populations, NOT
individuals, that are theorized to
evolve or change over time.
• Today, evolution is a term used to describe
biological change over time.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings