Darwin’s Theory of Evolution

What is Darwin’s Theory of Evolution? Introduced the idea that the environment (nature) selects an organisms traits – Natural Selection His theory of Natural Selection has many different parts… – Overproduction – Competition – Variations – Survival of the fittest – Inheritance

Overproduction Naturally occurring species have a tendency to produce far more offspring than can possibly survive

Competition Overpopulation results in competition for available resources. – Food – Water – Space – Mates There is a struggle for existence within the species

Variations Although offspring of a species are similar, there are differences that exist (variations) – Some of these differences have a high adaptive value – Some of these differences have a low adaptive value

Variations Variations that have a high adaptive value help the organism survive and pass on that trait. Variations that have a low adaptive value can cause an organism to die and not pass on that trait.

Variations in the species THE DIAGRAM ABOVE ILLUSTRATES THE CHANGE THAT OCCURRED IN THE FREQUENCY OF PHENOTYPES IN AN INSECT POPULATION OVER 10 GENERATIONS. A PROBABLE EXPLANATION FOR THIS CHANGE WOULD BE THAT OVER TIME THERE WAS 1. A DECREASE IN THE ADAPTIVE VALUE OF GENE A 2. AN INCREASE IN THE ADAPTIVE VALUE OF GENE A 3. AN INCREASE IN THE POPULATION OF THIS INSECT 4. A DECREASE IN THE MUTATION RATE OF GENE A

Survival of the Fittest Organisms with favorable adaptions survive – And pass on their genes Organisms with out these traits become sick and die. – Cannot pass on their genes Note: Fittest does not always mean the strongest!

Inheritance Individuals that survive (due to their favorable trait) will pass on the traits to their off spring! Survive  Reproduce  Species Continues

Example of Natural Selection: - Giraffes had many offspring - Offspring had different length necks (variations) - Offspring competed for limited resources - Long necks = survive Short necks = fewer survive Short necks = fewer survive (survival of the fittest) (survival of the fittest) - Long-necked trait was passed on to the future generations