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Today’s Objective:
• Identify natural selection as a mechanism for
Can be found in the book:
Pg. 393 - 399
Darwin and Natural Selection
• Charles Darwin (1809- 1882)
He was an English scientist and it took him
years to develop his theory of evolution.
• He began in 1831 at age 22 when he took a job as a
naturalist on the English ship HMS Beagle, which
sailed around the world on a five-year scientific
Darwin and Natural Selection
• As the ship’s naturalist, Darwin studied and
collected biological and fossil specimens at
every port along the route.
• The specimens were quite diverse, and he
became curious about possible relationships
among species.
• Breeding organisms with specific traits in
order to produce offspring with ideal traits is
called artificial selection.
(Intentional breeding for certain traits)
Who have we
studied that
bred organisms
A Goldendoodle
(Golden retriever/ Poodle)
Mendel and the pea
Darwin and Natural Selection
• Darwin observed that in
nature, the traits of
individuals vary in
• Variations are then
• Darwin hypothesized that there was a force in nature
that picked which traits are better for survival in a
Darwin and Natural Selection
• On the Galápagos Islands, Darwin studied many
species of animals and plants that are unique to
the islands but similar to species elsewhere.
• These observations led Darwin to consider the
possibility that species can change over time.
Darwin and Natural Selection
• He realized that individuals struggle to compete in
changing environmental conditions.
• What do individuals compete for?
• Only some individuals survive the competition and live
to produce offspring.
Darwin and Natural Selection
• Natural selection is the idea that organisms with
favorable variations survive, reproduce, and pass their
variations to the next generation.
• Organisms without these variations are less likely to
survive and reproduce.
Darwin and Natural Selection
• Darwin proposed the idea of natural selection to
explain how species change over time.
1.In nature, organisms
produce more offspring
than can survive.
Darwin and Natural Selection
2. In any population, individuals have variations.
• Fish, for example, may differ in color, size, and speed.
Darwin and Natural Selection
3. Individuals with certain useful variations, such as
speed, survive in their environment, passing those
variations to the next generation.
Whereas slower individuals would not survive to
Darwin and Natural Selection
4. Over time, offspring with FAVORABLE variations
make up most of the population.
The allele for the unfavorable variation may cease to
Why do you think more and more bad bacteria
(like the kind that cause sinus infections) are becoming
resistant to anti-biotics?
How do you think natural
selection will affect this species
of moth?
(both the same species, just
have variations)
Question 1
What is the difference between artificial and
natural selection?
Natural Selection:
Nature’s way of making sure the
best traits live on….
“Survival of the fittest”
• Recall that an adaptation is any variation that aids an
organism’s chances of survival in its environment.
• Examples are:
Thorns on plants
Special colorings for an organism
Enhanced night vision
• Learning about adaptations in mole-rats can help you
understand how natural selection has affected them.
• The ancestors of today’s common mole-rats looked
similar to this….
• Some ancestral rats may have avoided predators
better than others because of variations such as the
size of teeth and claws.
• Ancestral rats that
survived passed their
variations to offspring.
• The structural adaptations
of common mole rats
include large teeth and
long claws.
• These body parts enable
them to dig tunnels and
defend against predators.
• Over time, natural selection produced modern mole-rats.
• Their blindness may have evolved because vision had
no survival advantage for them.
• Some other structural adaptations are subtle.
• Mimicry is a structural adaptation that enables one
species to resemble another species.
• In one form of mimicry, a harmless species has
adaptations that result in a physical resemblance to a
harmful species.
• Another subtle adaptation is camouflage, an
adaptation that enables species to blend with their
• Because well-camouflaged organisms are
not easily found by predators, they survive to