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Theories of Evolution
The Origin of Species
How we came to be
Jean Baptiste de Lamarck
• French Scientist
• Theory of Acquired
Traits-Traits arise
during an organism’s
lifetime as a result of
experiences or
behaviors which are
passed to offspring
Example: Giraffes
Thomas Malthus
• In 1798, Malthus reasoned that
if the human population grew
unchecked, there wouldn’t be
enough living space and food
for everyone.
Charles Darwin
• At age 22, he was a naturalist
on the H.M.S. Beagle
• He collected fossils, specimens
and recorded his observations
Darwin’s Journals
He observed that fossils resembled living species from the same region,
and living species resembled other species from nearby regions
Galapagos Islands
His interest in
geographic distribution
of species was kindled
by a stop at the
Galápagos Islands west
of South America
He hypothesized that
species from South
America had colonized
the Galápagos and
speciated (become a
new species) on the
origin of new species ~ adaptation to the
(a) Cactus-eater
(c) Insect-eater
(b) Seed-eater
Alfred Wallace Charles Darwin
developed a theory of natural selection similar to Darwin’s
• In 1859 Darwin published
On the
Origin of Species
• Two Theories:
1. Descent with Modification
2. Modification by Natural
Ideas from The Origin of Species
Darwin explained three observations
about life:
The unity of life
The diversity of life
The match between organisms and
their environment
Descent with Modification
• Overproduction
• Variation
• Inheritance
• Selection
• Time
Evolution by Natural Selection
1. In nature, there is a tendency
toward overproduction.
Examples: mice, ants, fish, pine cone
2. The sizes of these populations
and the resources they need
remain constant over time.
• There is competition for
survival and reproduction.
• Not all offspring survive
• All life forms vary genetically
within a population. It is this
genetic variation upon which
selection works.
• Some of these variations
are due to genetic
differences which are
• Adaptations!
• Natural Selection- Individuals with
favorable variations for their
environment will live longer and
leave more offspring than
individuals with unfavorable
• The genetic makeup of the
resulting population will
change as it becomes better
adapted for its environment
over time.
• REMEMBER: The Population (the group of
the same species) will evolve, change over
• CHANGE does not happen in an individual's
life time, SO it is NOT the individual that
evolves, but the species
Survival of
the fittest!
Example of Natural
Selection—Peppered Moths
After The Industrial Revolution
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