Natural Selection

5 steps of natural selection

1. Individuals in a population vary in traits

2. Trait differences are heritable and are passed on to offspring

3. More offspring are produced than can survive

4. Individuals whose inherited traits give them a high probability of surviving and reproducing in a given environment are likely to leave more offspring (Survival of the fittest)

5. Unequal ability of individuals to survive and reproduce will lead to gradual changes in a population with favorable characters accumulating over generations

Natural selection

Differential survival and or fecundity (reproductivity) of individuals with different forms or traits as a result of interactions with biotic and abiotic environment (INDIVIDUAL)

Evolution

Gradual changes in the characteristics of a population, with favorable characters accumulating over generations (POPULATION)

Misconceptions about natural selection

• INDIVIDUALS do NOT EVOLVE (populations evolve)

• Does not involve organisms TRYING to adapt

• Does NOT give organisms what they need to survive

• Natural selection favors traits that ENHANCE survival and reproduction in a new environment

Fitness

A relative measure of how well an organism’s traits, behaviors, and genetic characteristics contribute to its reproductive success and the transmission of its genes to the next generation (Keep the context in mind)

Absolute fitness

Average number of offspring of a given type per parent of the given type

Relative fitness

Average contribution to the offspring generation relative to the contribution of another type

Variation

Individuals in a population have different traits

Inheritance

Differences in traits are heritable and transmitted from parent to offspring

Traits

Must vary within the population. Anything that can be quantified or characterized (structure, color, physiology, life history, etc.)

Selection sorts based on PHENOYTPE

3 requirements for natural selection

Variation - Individuals in a population have different traits

Inheritance - Differences in traits are heritable and transmitted from parent to offspring

Differential reproductive success - individuals with certain traits are more successful than others at surviving and reproducing

Convergent evolution

When two taxa become similar in a trait or set of traits even though they are from unrelated lineages. Often the result of natural selection under similar environmental conditions

Adaptation

A trait that has been shaped by natural selection and improves an organism’s ability to survive and reproduce in an environment (environment can be biotic or abiotic