The Theory of Natural Selection

Review - Theory A well-supported explanation for why something happens in nature Supported by observations, inferences, hypothesis, laws & principles

Evolution How a species changes over time

What scientific explanation can explain the diversity (many types) of life on Earth?

Biodiversity – the wide range (types) of living things

Charles Darwin English naturalist (1800’s) Proposed the theory of natural selection to explain how evolution occurs

Selection A process of determining which traits are going to be advantageous/good and which is deleterious/bad Artificial- people choose traits (dogs, corn, etc) Natural- the environment chooses

Key Processes of Natural Selection Genetic variation Overproduction of offspring Struggle for survival Differential survival & reproduction

Genetic Variation Inherited variation of traits is present among individuals of a population

Genetic Variation

Mutation A random change in DNA creating new traits/alleles Produces variation Allele- different forms of a gene (represented by letters upper case= dominant Lower case = recessive

Overproduction of Offspring Populations have the potential to produce more offspring than an areas resources can possibly support

Overproduction of Offspring

Struggle for Survival A individual’s survival depends on its ability to compete successfully for food, water and other resources and to avoid predators & disease.

Differential Survival & Reproduction Individuals with the most successful traits (highest fitness) in their environment are more likely to survive Over many generations the population changes as the frequency of the trait increases or decreases

Fitness A measure of how successful an organism survives and reproduces, making healthy babies. High Fitness = many babies Low Fitness = few babies

Adaptation An anatomical, physiological or behavioral change that improves a population’s ability to survive