EvolutionEvolution – change in inherited characteristics/traits in a

population over several generations

• All organisms descend from a common ancestor or common gene pool

• “Descent with Modification”

• Only occurs when there is a change in allelic frequency (# of dominant v. #of recessive) in a given population over time

• Genetic equilibrium = no evolution (means allelic frequencies are equal one generation to the next)

Adaptation – feature that is common in a population because it provides an improved function or behavior for survival

• Gives a greater fitness (favorable trait)• Created by natural selection (survival of the

fittest)• Can be structural or physiological• Examples: camouflage, mimicry, toxicity development, echolocation, resistance build up

Evidence of Evolution• Fossil record• Anatomy– Homologous structures– Analogous structures– Vestigial structures

• Embryology/developmental• Biochemistry– DNA/amino acid sequence– Cytochrome C

Mechanisms of Evolution1) Mutations – allows for greater variation and new

variations

2) Migration – flow of genes in and/or out of a population (gene flow)

• Immigration = movement into a population (increases allelic frequency)

• Emigration = movement out of a population (decreases allelic frequency)

• Creates variation

3) Non-random mating – eliminates variations (independent assortment and genetic recombination in meiosis)

Mechanisms of Evolution4) Genetic drift – chance changes from generation to

generation (affects small populations more)– Caused by disease, natural disasters, climate change,

recessive traits– Must have genetic variation

5) Natural selection (most significant cause) – choosing of a certain variation over another– Survival of the fittest– Must have genetic variation

Variation + differential reproduction + heredity = natural selection

Natural SelectionFitness – describes how good a particular genotype is

at leaving offspring in the next generation**Survival of the Fittest**

• Determined by environment/habitat• Includes ability to survive, find a mate, and produce

offspring

3 types of Natural selection:• Stabilizing – favors the average individuals (hybrids)• Directional – favors one extreme of the trait• Disruptive – favors both extremes of the trait

Artificial selection – purposely choosing desired traits of an organism and reproducing them• Done by farmers and breeders• Creates purebred lines• “Selective breeding”

Coevolution – 2 or more species evolve together or cause each other to evolve• Predator/prey or parasite/host• Competitive species• Mutualistic species

Microevolution – evolution on a small scale (a single population) • House sparrows adjusting to North American climate• Mosquitos evolving to global warming• Insects/bacteria evolving resistance to pesticides/antibiotics

Macroevolution – evolution on a large scale• Multiple species• Large time scale

Speciation – formation of a new species

Species – group of organisms that can interbreed and produce fertile offspring

Causes of SpeciationGeographic isolation - population is prevented from interbreeding by a physical barrier• when rivers change course, mountains rise, continents drift,

roads are built, part of a forest cut down• what was once a continuous population is divided into two or

more smaller populations.

Reproductive isolation - behaviors and physiological processes that prevent the members of a population or species from producing fertile offspring• Can be a difference in mating ritual, non-compatible

genitals, or produces infertile offspring

Rates of SpeciationGradualism – change occurs over a long period of time (several generations/100’s of years)

Punctuated equilibrium – change occurs quickly, in rapid burst followed by periods of genetic equilibrium

Patterns of EvolutionDivergent evolution – two species that once were similar evolve to be very different• Called adaptive radiation when caused by differing habitat• Darwin finches• Supported by homologous structures

Convergent evolution – two unrelated species that once were different evolve to be very similar• Dolphins and sharks• Supported by analogous structures