Charles Darwin developed his theory of evolution based on four observations of organisms and populations: 1) offspring are produced in greater numbers than can survive, 2) populations remain stable in size, 3) variation exists among individuals of the same species, and 4) some characteristics are inherited. His two deductions were that organisms struggle for survival, with only the best adapted surviving ("survival of the fittest"), and these survivors pass on their useful adaptations to offspring through natural selection.

1. Charles Darwin
and the Theory of Evolution

2. Charles Darwin developed his
theory of evolution using four
observations and two
deductions.

3. Observation #1:
All organisms produce more
offspring than survive to
adulthood.

4. For example: a female rabbit
can produce up to seven
kittens in a litter, but they don’t
all survive to become adults.

5. Observation #2:
Populations remain more
or less constant in
numbers.

6. Example:
If an island has a
population of 75 mice . .
. the number of mice
that can be counted on
the island at any one
time always stays at
about 75.

7. Observation #3:
Members of the same
species show variation
in characteristics.

8. Iguanas in a
population may
be of the same
species but
have different
colored skin and
markings.

9. Observation #4: Some
characteristics are inherited
and are passed on to the
next generation.

10. Example: finches with a
beaks of a certain shape
pass on that characteristic to
their offspring.

11. Darwin came to 2 deductions as a
result of his observations.

12. Deduction #1: All organisms are
involved in a struggle for survival
and only the best adapted
survive. This is also know as
“Survival of the Fittest”.

13. The individuals that are best adapted
to their environment are most likely to
survive and have a chance to
reproduce. These animals pass off
their useful adaptations to the next
generation.
Male African Lion

14. Animals that have the
fewest adaptations for
survival do not live long
enough to breed. They
never have offspring.
Their weaknesses are
not passed on the the
next generation.

15. Deduction #2: Organisms that
survive are more likely to
reproduce, and therefore pass
on their useful adaptations to
their offspring.

16. These ideas formed the basis
of Darwin’s theory of evolution.
This is also referred to as
natural selection.
Male African lion Silverback mountain gorilla

17. Darwin concluded that natural
selection explained how organisms
gradually changed and evolved
into new species.

18. At the time of
publishing Darwin
found it difficult to get
his theory accepted,
as it was difficult to
prove.

19. Other scientists at the time
wanted Darwin to prove that
individuals passed their
characteristics to their
offspring.

20. Since the 1800’s, we now have a
greater knowledge of genetics. Much
of what we now know about genes and
heredity support Darwin’s theory.