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Evolution
Change in allele frequency over time.
Why do we resemble our parents?
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Hereditary – passing of traits from parent
to offspring
Traits – an aspect of an organism that can
be described or measured.
DNA - Gene – Chromosome
You inherit ½ chromosomes from Mom
and ½ from Dad
Dominant vs. Recessive
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Dominant – gene that determines
expression of a genetic trait; the trait shows
up
Recessive – gene that is overruled by a
dominant gene; trait is masked
Genotype vs. Phenotype
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Genotype – genes of an individual
Phenotype – observable traits
Evolution
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A scientific theory
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Well supported testable explanation of
phenomena that have occurred in the natural
world.
The change in allele (gene) frequencies
over time.
Charles Darwin
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Person credited with our understanding of
evolution.
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Took a voyage on the H.M.S. Beagle
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Made observations and collected evidence
that led him to propose a hypothesis about
how life changes over time.
Section 15-1
Figure 15–1 Darwin’s Voyage
Collection of Evidence
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Each time the ship stopped, Darwin went
ashore to collect plant and animal
specimens.
He studied his large collection of
specimens and kept a journal with his
thoughts and observations.
During his travels Darwin started to believe
that he was coming across a scientific
explanation for the diversity of life on
Earth.
Darwin’s Observations
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Great Diversity
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Patterns of Diversity
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Plants and animals seemed to be suited for
whatever environment they inhabited.
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Why do some organisms live in one place but not
in another? (ie. Why no rabbits in Australia? No
kangaroos in England?)
Darwin’s Observations
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Living Organisms and Fossils
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Fossils = preserved remains of ancient
organisms
Fossils resembled live organisms
Why had those species disappeared?
 Is there a relationship between fossils and living
organisms?
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The Galapagos Islands
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West of South America
Although the islands were close together,
they had very different climates.
Darwin studied a variety of Galapagos
organisms
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Finches
Tortoises
Marine Iguanas
Variety of Plant Species
Giant Tortoises of the
Galápagos Islands
Section 15-1
Pinta
Pinta Island
Tower
Marchena
Intermediate shell
Fernandina
James
Santa Cruz
Isabela
Santa Fe
Hood Island
Floreana
Isabela Island
Dome-shaped shell
Hood
Saddle-backed shell
Darwin’s Reflections on His
Findings
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Darwin observed that the characteristics of
many animals and plants varied among the
different Galapagos Islands.
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He began to wonder if these organisms on
the different islands had once been a single
species.
Key Concept Questions
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What is evolution?
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What was Charles Darwin’s contribution to
science?
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What pattern did Darwin observe among
organisms of the Galapagos Islands?
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Why did Darwin think the organisms of the
Galapagos Islands were related?
On the Origin of Species
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Darwin’s book where he published his
ideas regarding Earth’s biodiversity and
how life changes over time.
Why do some individuals die early,
but not others?
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Struggle for Existence
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Members of each species compete for
necessary resources
Food
 Space
 Etc.
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Those that are faster, better camouflaged, or
better protected are more likely to survive
Evolution by Natural Selection
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Survival of the Fittest
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Fitness = the ability of an organism to survive
and reproduce
Adaptation = inherited characteristics that
increase an organisms fitness
Those that are best able to survive and
reproduce are the fittest, hence Survival of
the Fittest
Natural Variation &
Natural Selection
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Natural Variation= differences among
individuals of a species
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Natural Selection = the differences in
survival and reproduction among members
of a population.
Evolution by Natural Selection
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Over many generations we will see a decrease of
animals with unfavorable traits.
Darwin thought there were several factors involved
in natural selection
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The presence of variation
Hereditary basis of such variation
Tendency for population to increase
“struggle for survival”
A difference in inherited traits passed on to each generation
Key Concept Questions
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What is natural variation?
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How did we observe natural variation in our
“Survival of the Fittest” lab? …in this classroom?
How are artificial selection and natural selection
different?
Does natural selection act on an individual or a
population?
What makes an organism fit?
Can an organism be fit in one environment and
unfit in another? Explain.
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Provide evidence from lab