Bio - M7 Natural Selection

Evolution

Biological populations change over time

Theory

System of well-supported ideas based on tested hypothesis

Erasmus Darwin

Charles Darwin’s grandfather. Proposed idea of evolution but lacked a viable mechanism.

Jean-Baptiste Lamarck

Proposed mechanism of evolution by inheritance of acquired characteristics

Alfred Russel Wallace

Co-discoverer of theory of evolution, Independently arrived at the idea of evolution by natural selection in 1858.

Population must show variation in a trait

Darwin’s first postulate of natural selection

Some of a population’s variation must be heritable

Darwin’s second postulate

More individuals must be born than can survive to reproduce (leads to competition)

Darwin’s third postulate

Non-random survival. Variation in the trait must affect survival and reproduction (fitness) of individuals

Darwin’s fourth postulate

Natural selection

Mechanism by which evolution can occur

Gene pool

Sum of total genetic variation within a population

Mutation

Source of all genetic variation. Includes recombination and independent assortment.

Conjugation

Source of genetic variation in bacteria. The temporary union of two bacteria or unicellular organisms for the exchange of genetic material. 

Lateral gene transfer

Source of genetic variation in bacteria. Movement of genetic material between organisms that are not parent and offspring.

Fitness

Ability to pass alleles to next generation. Ability to survive and to reproduce.

Directional selection

Selection that favors one extreme of range of variation of phenotypes

Stabilizing selection

Selection that favors the mean phenotype.

Disruptive/diversifying selection

Selection that favors extreme phenotypes.

Positive frequency-dependent selection

Selects for the most common phenotype. Variation in population decreases over time.

Negative frequency-dependent selection

Selects for the rarest phenotype. Variation in population increases overtime.

Sexual dimorphism

Sexes of the same species exhibit different characteristics (not directly involved in reproduction)

Male-male competition

Includes direct combat, ritualized fighting, male guarding, or sneaker males for access to mates

Female choice

Favors traits that show parental care, resource provision, are attractive, or in good health for sexual selection

Sexual selection

Specifically favors traits that help individuals get mating partners rather than traits that help with survival

Colonization

Presence of bacteria without any symptoms