Evolution and Natural Selection

Evolution through
Natural Selection
Mrs. Dignan’s Biology Class
The Process of Evolution
Evolution is change
over time.
 It occurs within
populations, not
individuals.
 It occurs over
generations, not
within individual
lifespans.
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The Theory of Evolution through
Natural Selection
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Charles Darwin first proposed
the Theory of Evolution
through Natural Selection in
his book, The Origin of the
Species.
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The Theory of Evolution
through Natural Selection
explains how modern
organisms have evolved over
time from common ancestors.
Before Darwin, people thought
that all of the creatures on
Earth were created by God
exactly as they appear today.
A Note about Theories

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A scientific law is a general
description of the way things
work in the natural world. (exp
– gravity)
A scientific theory is a welltested explanation that
connects a broad range of
observations (exp – evolution,
germ theory)
Theories are NOT hypotheses
or untested ideas.
Theories do NOT become laws
after they have been tested.
Like other theories, evolution
is supported by a great deal of
evidence.
Back to Darwin…
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Darwin was a naturalist.
He traveled the world by
boat and made detailed
observations about
species that Europeans
had never even imagined.
This voyage around the
world sparked his
thinking about
relationships between
species.
On the Galapagos Islands
He was particularly interested in
the wide variety of little birds.
 Each island was inhabited by a
number of slightly different
species.
 Each species of finch had a
different type of beak that allowed
it to eat certain types of food.

4 Observations that lead to
Darwin’s Theory of Evolution by
Natural Selection
Organisms can produce more offspring than
they can support.
2. Any environment has a finite supply of
resources.
3. Individuals have natural variation in their traits,
due to mutations and genetic recombination.
4. Those individuals most suited to their
environment tend to survive and pass on their
traits (this is natural selection!).
1.
“Survival of the Fittest”

What do we mean by fittest?
Who is more fit?
George Clooney
Jack Black
George Clooney

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5’ 10”
170 lbs
52 years old
Several years winner
of the “sexiest man
alive” award
Accomplished actor
and director
Quote

“After doing One Fine
Day and playing a
pediatrician on ER, I'll
never have kids. I'm
going to have a
vasectomy.”
Jack Black
5’9”
 210 lbs
 45 years old
 Accomplished
comedian, actor, and
musician.

Quote

“Never for a second did I
think of myself as the sexiest
guy in the world. When I was
a kid, I thought I was the
strongest man in the world.
Then, the fastest runner and
then the smartest person in
the world. One by one my
delusions got shut down. Now
I just see myself as the
lamest guy in the world.“
Who is more fit evolutionarily?
George Clooney
Jack Black
Evolutionary Fitness is…
The ability to survive to adulthood
 AND
 The ability to reproduce and produce
healthy, fertile offspring.
 If an organism does not have both of
these traits, their genes will not get
passed on and they play no role in the
future of their species.

Natural Selection is…
The process by which heritable traits
become more or less common in a
population depending on whether or not
that improve an individuals evolutionary
fitness.
 Nature selects which individuals survive
and which don’t.
 Survival of the “fittest”!

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A desert environment may select for plants that are
small, without leave, and that can ward off
predators (like cacti)

A rainforest environment may select for plants
that are tall, with lots of leaves that capture the
sunlight