Charles Darwinand the Theory of Evolution

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

Observation #1:

All organisms produce more offspring than survive to adulthood.

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

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

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.

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

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

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

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

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

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”.

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

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.

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

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

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

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

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

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.