Download 03 Natural Selection Notes

Natural Selection Notes
Essential Question: How does
natural selection lead to
evolution?
The Theory of Natural Selection
• Adaptation – a beneficial trait that allows an
individual to survive better than others
• Adaptations may help individuals to compete for
food or other resources or to avoid predators.
• Those individuals are then also able to have more
offspring.
• If these traits are hereditary, then the offspring
would also have these traits.
• In the next generation, there will be more
individuals with the beneficial trait.
• Natural selection – Individuals with
better adaptations have a better chance
of survival and are able to produce more
offspring, therefore, future generations
will have more individuals with that
trait.
5 Principles of Natural Selection
1. Variation: individuals in a population differ from one
another.
2. Heritability: individuals pass down their traits to their
offspring.
3. Struggle for survival: limited resources, predators and harsh
conditions all make survival difficult. Some individuals will be
better equipped to survive than others.
4. Overproduction: more offspring are produced than can
survive.
5. If these traits are beneficial and allow an individual to leave
more offspring, more offspring in the next generation will have
the beneficial trait.
5 Principles of Natural Selection
1. Variation: individuals in a population differ from one
another.
5 Principles of Natural Selection
2. Heritability: individuals pass down their traits to their
offspring.
5 Principles of Natural Selection
3. Struggle for survival: limited resources, predators and
harsh conditions all make survival difficult. Some individuals
will be better equipped to survive than others.
5 Principles of Natural Selection
4. Overproduction: more offspring are produced than
can survive.
5 Principles of Natural Selection
5. If these traits are beneficial and allow an
individual to leave more offspring, more
offspring in the next generation will have the
beneficial trait.
Examples of Natural Selection:
The Evolution of The Polar Bear
Our story begins with the Polar Bear’s
closest living relative – the Brown Bear
Around 300,000 years ago a small group of
Brown Bears became reproductively
isolated from the rest of the population
This small founding
population of
Brown Bears were
able to survive and
reproduce living in
the Arctic Tundra.
After MANY
generations, a
random genetic
mutation occurred
...
Because of the genetic mutation, a litter of
Brown Bears exhibited WHITE coloration
How do you think the white fur color affected
these bears chances of surviving long
enough to have cubs of their own?
REMEMBER: Natural Selection Rests on 5 Premises:
1) There is variation in the traits of
individuals within a population
2. Individuals pass down their traits to their
offspring.
3. Overproduction: more offspring are
produced than can survive.
4. There is a struggle for survival: limited
resources, predators and harsh conditions all
make survival difficult. Some individuals will be
better equipped to survive than others.
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5. If these traits are beneficial and allow an
individual to leave more offspring, more
offspring in the next generation will have the
beneficial trait.
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What Happened?
Through reproductive isolation and
natural selection . . .
one species evolved into another new
species because it was better adapted to
its new environment
Evolution
• Evolution is the build up of genetic changes in a
population of a species over many generations.
• Natural selection leads to small changes that build up
and add up to large changes in species – this is
evolution.
In other words: natural selection leads to evolution.
• Microevolution – small changes in a species
(attributed to natural selection)
• Macroevolution – development of a whole new
species, typically called evolution