Evolution Unit 6

Evolution

Evolution is the change in the heritable traits of populations over generations.

Darwin's theory

Charles Darwin proposed that all species of organisms arise and develop through natural selection, where traits that enhance survival and reproductive fitness are passed on more frequently.

Natural selection

Natural selection is the process where organisms produce more offspring than can survive, variation exists among individuals, some variations are more favorable, and favorable traits become more common in future generations.

Mechanism of natural selection

Natural selection occurs in populations, not individuals, and acts on phenotypes, not genotypes directly.

Environmental changes

Environmental pressures can shift trait advantages, altering population genetics over time.

Four Postulates of Natural Selection

1. Variation exists among individuals; 2. Traits are heritable and can be passed from parents to offspring; 3. Differential survival and reproduction exist among individuals; 4. Favorable traits increase in frequency due to higher reproductive success.

Convergent evolution

Convergent evolution is when unrelated species evolve similar traits due to similar environments (e.g. wings in birds and insects).

Divergent evolution

Divergent evolution is when related species evolve different traits due to different environments.

Analogous structures

Analogous structures are similar in function, different in structure, and are a result of convergent evolution.

Homologous structures

Homologous structures are similar in structure, different in function (e.g. human arm and whale flipper), and are a result of divergent evolution.

Fossils

Fossils show changes in organisms over time.

Comparative anatomy

Comparative anatomy studies homologous structures that suggest common ancestry.

Molecular biology

Molecular biology examines similar DNA and proteins that indicate evolutionary relationships.

Embryology

Embryology studies similar embryonic development patterns among different species.

Gene pool

The gene pool is the total collection of genes in a population.

Allele frequency

Allele frequency is the proportion of an allele in the gene pool.

Genotype frequency

Genotype frequency is the proportion of each genotype among individuals.

Five conditions for H-W Equilibrium

1. No mutation; 2. No gene flow (immigration); 3. Random mating; 4. No genetic drift (large population); 5. No natural selection.

Allele frequencies equation

The equation for allele frequencies is $p + q = 1$.

Genotype frequencies equation

The equation for genotype frequencies is $p^2 + 2pq + q^2 = 1$.

Genetic drift

Random changes in allele frequencies, especially in small populations

Founder effect

Occurs when a small group of individuals breaks off from a larger population and establishes a new population in a new location

Bottleneck effect

Happens when a large population is suddenly reduced in size

Gene flow

Movement of alleles between populations, increases genetic diversity

Mutation

Random changes in DNA that introduce new genetic variation

Speciation

The process by which new species arise

Allopatric speciation

Occurs due to geographical isolation

Sympatric speciation

Occurs without geographical barriers

Reproductive isolation

Prevents gene flow between populations

Prezygotic isolation

Occurs before fertilization and includes temporal, behavioral, mechanical isolation

Postzygotic isolation

Occurs after fertilization and includes hybrid sterility/inviability

Adaptive radiation

Rapid diversification of a species into multiple forms to occupy different niches

Phylogeny

The evolutionary history and relationships among species

Phylogenetic trees

Diagrams that represent evolutionary relationships

Cladistics

A method of classifying species based on common ancestry

Descent with modification

How natural selection works, leading to evolution

Reproductive success

Depends on an individual's characteristics.

Natural selection acts on

Individuals within a population.

Population changes over time

As the percentage of individuals inheriting favorable traits increases.

Evolution of individuals

An individual cannot evolve, but a population can.

Controlled breeding

Modifies organisms.

Artificial selection

Selective breeding of domestic plants and animals to produce specific desirable features.

Natural selection today

Evolution by natural selection occurs today.

Evidence of natural selection

Scientific observation and experimentation provide additional evidence.

Brighter coloration

Can evolve when fewer predators are present.

Chance mutations

The variations on which natural selection works are produced by chance mutations that arose spontaneously.

Adaptation to environment

Natural selection selects for organisms that are best adapted to a particular environment.

Context of natural selection

Natural selection does not select for the 'best' in any absolute sense, but only for what is best in context of a particular environment.