Download Natural Selection and Evolution

Charles Darwin and
The Origin of Species
Jean Baptiste Lamarck argued that fossils were
relics of the ancestors of modern species.
Lamarck believed
that organisms
acquired new traits
over their lifetimes
and then passed
them on to their
offspring. He called
this the inheritance
of acquired characteristics.
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Charles Darwin and
The Origin of Species
Darwin argued that evolution—heritable
changes in organisms over time—
explained the origin of all organisms on
Earth.
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Darwin was inspired by:
• His travels on the Beagle.
• The work of geologist Charles Lyell
• The work of economist Thomas Malthus
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Darwin’s Galápagos Island finches were significant
because they provided what appeared to be an example
of how a single species could evolve into multiple
species, each adapted to a different lifestyle.
The 13 species of finches he found varied in beak size and
shape, depending on their diet.
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How Natural Selection Works
• In any population, individuals have traits, many of
which show variation.
• Traits that are determined by genes are heritable.
• Advantageous traits benefit an organism and allow it
to leave more offspring—this is natural selection.
• Advantageous traits become more common in a
population, resulting in adaptation.
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How Natural Selection Works
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How Natural Selection Works
Adaptations are traits that make an organism better
suited to living in and reproducing in its
environment.
• Many adaptations help organisms survive.
• Some adaptations help organisms attract mates—
this is called sexual selection.
• Other adaptations relate to bearing and raising
offspring.
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Natural Selection
• How Natural Selection Works
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Animal Adaptations to Heat and
Cold
Animals thermoregulate:
• Surface-to-volume ratio is an
important factor in heat balance.
• Bergmann’s Rule says that
animals found in cold habitats
are often larger than related forms
in warm habitats.
• Allen’s Rule states that appendages
will be longer/larger in hot-climate
animals and shorter/smaller in
cold-climate animals.
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Animals also control body temperature with:
• Coloration
• Insulation
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How Natural Selection Works
Natural selection is classified into three
modes:
• Directional selection
• Stabilizing selection
• Diversifying selection
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The Modern Synthesis incorporates
modern genetics into Darwin’s theory of
evolution.
It focuses on evolution as changes in the
allele frequencies of genes over time.
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Four different mechanisms produce
evolution:
•
•
•
•
Natural selection
Mutation pressure
Genetic drift
Migration
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How Species Form
A species is a group of organisms whose
members can interbreed with each other
but not with members of other species.
The key to speciation—the development of
new species—is the evolution of
reproductive barriers that prevent two
groups of organisms from interbreeding.
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How Species Form
There are two kinds of reproductive
barriers:
• Prezygotic reproductive barriers
prevent members of different species from
mating in the first place or prevent
fertilization from occurring.
• Postzygotic reproductive barriers
prevent hybrids from surviving or from
reproducing if they do survive.
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How Species Form
CHECK YOUR NEIGHBOR
Is a mule an example of a prezygotic
reproductive barrier or a postzygotic
reproductive barrier?
Explain your answer to your neighbor.
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How Species Form
CHECK YOUR ANSWER
A mule provides an example of a
postzygotic reproductive barrier. It is the
hybrid offspring of two different species, a
horse and a donkey. Mules are sterile and
cannot reproduce.
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How Species Form
New species may develop as a result of:
• Allopatric speciation (geographic barriers dividing
a population in two)
• Sympatric speciation (speciation without a
geographic barrier).
Examples: hybridization and chromosomal changes,
such as polyploidy.
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Speciation
• Animation
• Animation II
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Evidence of Evolution
Evidence for evolution includes:
• Natural selection in action
• Human-imposed artificial selection (e.g.,
domesticated animals and plants)
• Shared anatomy, patterns of development, and DNA
among living creatures
• The fossil record
• Biogeography
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Artificial Selection
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Evidence of Evolution
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Evidence of Evolution
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Does Evolution Occur Gradually or
in Spurts?
Gould and Eldredge proposed the theory of
punctuated equilibrium—species maintain
stability (“equilibrium”) for long periods and
then evolve in rapid bouts (“punctuated”) that
occur during speciation.
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Animations
• Various Animations
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