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Natural Selection
Objective 2-3
Artificial Selection (Selective
• Nature develops all traits
• Humans choose which traits they like and
use selective breeding to manipulate the
• Darwin witnessed this in domestic
animals: dogs, cats, cows, etc.
• He used this observation to develop the
concept of Natural Selection
Natural Selection
Darwin defined how nature chooses what
lives and what dies as Natural Selection:
1. Struggle for existance
Animals are always competing to survive
2. Survival of the Fittest
Those animals with the best traits to survive
in their specific environment are more likely
to live and reproduce
Their children would also have the useful traits
Natural Selection
3. Descent with Modification
Each generation is slightly different from the
one before it
After 1,000s of generations a species can
look very different
Common Descent: if you go back in time far
enough, every living thing is related
Darwin’s Theory of Evolution
1. Individual organisms differ, and some of
this variation is heritable.
2. Organisms produce more offspring than
can survive.
3. Because more organisms are produced
than can survive, they compete for
limited resources.
Darwin’s Theory of Evolution
4. Individuals best adapted to their
environment survive and reproduce most
successfully. These organisms pass
their heritable traits to their offspring.
5. Species alive today are descended with
modification from species that lived in the
distant past. If you go back far enough
all life on this planet is linked in one great
tree of life.