Natural Selection

Charles Darwin

Charles Darwin

• Was a “naturalist” • Studies organisms and noted differences

(diversity) in their appearance around the world.

• Spent a large period of time studying organisms on the Galapagos Islands in the Pacific off the coast of South America

Darwin

• In 1859, Darwin published his findings in a book titled “The Origin of Species”

Darwin

• Darwin identified the change in species over time to be caused by “Natural Selection.”

• In this process, individuals who are better adapted to their environment are more likely to survive thus reproduce than other members of their species. The adaptations and traits that an organism possesses will be passed on to their offspring.

Natural Selection

Darwin noted 5 “mechanisms” that drove natural selection:

• Overproduction• Variations• Competition• Selection• Environmental Change

Overproduction

Simply stated: more offspring are produced than can survive in a species.

Variations

• These are differences among individuals in a population.

Competition• Competition involves the “fight” for limited

resources such as food, water, territory, and mates.

• It is most often in an “indirect” form.• Example: Zebras and Wildebeast eating the

same grass.• Sometimes it is direct: Lions and Hyenas

fighting over a kill, or male’s fighting for mates.

Competition

Selection

• Variations make organisms more or less likely to survive. The environment “selects” these organisms based on their variations.

• Organisms that are better suited to live in an environment will survive, reproduce and pass on their traits.

• Over time, this can lead to changes in a species.

Selection

Environmental Change

• Changes in the environment can affect the survival rate of individuals in a species.

• Examples: Peppered Moths, Desert Lizards, Pollution affecting water quality.