Fig. 2.7
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2.1 Darwin’s Voyage on HMS Beagle
In 1831, Charles Darwin
took on the role of
naturalist of the ship
HMS Beagle
Fig. 2.1
The Beagle set sail on a
five-year navigational trip
around the world
Charles Darwin (1809-1882)
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2.1 Darwin’s Voyage on HMS Beagle
Darwin studied a wide variety of plants and
animals across the globe
Particularly on the Galapagos Islands
In 1859, he published his book On the
Origin of Species
In it he proposed that evolution occurs
through natural selection
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13.1 Evolution: Getting from
There to Here
Natural selection, the process that leads to evolution,
occurs in steps
1. Gene variation exists among individuals in a population
2. This variation is often passed to offspring
3. All populations overproduce offspring
4. Individuals with traits that aid survival and reproduction
have a better chance of contributing to the next generation
5. Over time, the population changes such that the traits of
the more successful reproducers are more prevalent
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13.1 Evolution: Getting from
There to Here
Macroevolution
Evolutionary change on a grand scale
Encompasses the origins of new species and
major episodes of extinction
Microevolution
Evolutionary change on a small scale
Encompasses the genetic changes that occur
within a species over time
These changes are the result of changes in
gene frequencies
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13.2 The Evidence For Evolution
Evidence for evolution comes from the following
Fossil record
Molecular record
Anatomical record
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Fossils have been
found linking all
the major groups
The forms linking
mammals to
reptiles are
particularly well
known
Fig. 13.4 Whale
“missing links”
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The greater the
evolutionary distance
Fig. 13.5 Molecules
reflect evolutionary
divergence
The greater the number
of amino acid differences
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This same pattern of
divergence is seen
with DNA sequences,
such as that of the
cytochrome c gene
The changes appear
to accumulate at a
constant rate
This phenomenon
is referred to as a
molecular clock
Fig. 13.6
Note: Different proteins evolve at different rates
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Anatomical Record
All vertebrates share a basic set of developmental
instructions
Fig. 13.7
Relict
developmental
forms
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13.5 Why Allele Frequencies Change
Microevolution – five evolutionary forces can
significantly alter the allele frequencies of a
population
1.
2.
3.
4.
5.
Mutation
Migration
Genetic drift
Nonrandom mating
Selection
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Mutation
Table 13.1
Errors in DNA
replication
The ultimate source of
new variation
Mutation rates are too
low to significantly
alter allele frequencies
on their own
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Migration
Table 13.1
Movement of
individuals from one
population to another
Immigration: movement
into a population
Emigration: movement
out of a population
A very potent agent of
change
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Genetic Drift
Random loss of alleles
Table 13.1
More likely to occur in
smaller population
Founder effect
Small group of individuals
establishes a population
in a new location
Bottleneck effect
A sudden decrease in
population size to natural
forces
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Nonrandom Mating
Mating that occurs more
or less frequently than
expected by chance
Table 13.1
Inbreeding
Mating with relatives
Increases homozygosity
Outbreeding
Mating with non-relatives
Increases heterozygosity
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Selection
Some individuals leave
behind more offspring
than others
Table 13.1
Artificial selection
Breeder selects for
desired characteristics
Natural selection
Environment selects for
adapted characteristics
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13.8 Selection on Color in Guppies
Poecilia reticulata (guppy) is a popular aquarium fish
In nature, it is found in small streams in NE South
America and in mountainous streams in Trinidad
Due to dispersal barriers, guppies can be found in
two different pool environments
Below waterfalls, where risk of predation is high
Above waterfalls, where risk of predation is low
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Fig. 13.19 The evolution of protective coloration in guppies
A voracious
predator of guppies
Rarely preys
on guppies
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In low-predation pools,
males
Display gaudy colors
and spots
Reproduce at a late age
Attain larger adult sizes
In high-predation pools,
males
Exhibit drab coloration
Reproduce younger
Attain relatively small
adult sizes
In the absence
of predators,
larger more
colorful fish
may produce
more offspring
In the presence
of predators,
smaller and less
colorful fish are
likely favored by
selection
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The evolution of these differences in guppies was
experimentally tested in laboratory greenhouses
Fig. 13.20
Indistinguishable from
low-predation controls
Same results were obtained
in field experiments
Smaller and
drab in color
Thus, natural selection can lead to rapid evolutionary change
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