Evolution: Lamarck, Darwin & Natural Selection

• Evolution is the change in the heritable characteristics of biological populations over successive generations.

Lamarck's Theory of Evolution

• Evolution occurs through the inheritance of acquired characteristics.
• Organisms can pass on traits acquired during their lifetime to their offspring.
• This theory is largely discredited.

Darwin's Theory of Evolution

• Evolution occurs through natural selection.
• Individuals with advantageous traits are more likely to survive and reproduce.
• These advantageous traits become more common in the population over time.

Natural Selection

• Natural selection is the process where organisms better adapted to their environment tend to survive and reproduce more successfully.
• Results in adaptive evolution.
• Key components include variation, inheritance, selection, and time.

Genetic Drift

• Genetic drift is the change in the frequency of a gene variant in a population due to random sampling of organisms.
• Genetic drift can cause significant changes in small populations.
• Alleles can be lost entirely, reducing genetic variation.

Gene Flow

• Gene flow, also known as gene migration, is the transfer of genetic variation from one population to another.
• Can introduce new alleles into a population.
• Increases genetic variation within a population.

Evidence of Evolution

• Fossil records show the change of organisms over time.
• Comparative anatomy reveals similarities and differences in structures of different species.
• Embryology shows similarities in the development of different organisms.
• Molecular biology examines DNA and protein similarities.

Homologous Structures

• Homologous structures are similar in different species because of descent from a common ancestor.
• May have different functions.
• Example: the limb bones in humans, bats, and whales.

Analogous Structures

• Analogous structures are similar in different species because of convergent evolution, not common ancestry.
• Have similar functions.
• Example: the wings of bats and insects.

Gradualism

• Gradualism is the theory that evolution occurs slowly but steadily.
• Small changes accumulate over long periods of time.

Punctuated Equilibrium

• Punctuated equilibrium is the theory that evolution occurs in bursts of rapid change, separated by long periods of stasis.
• Rapid change often follows a major environmental change or isolation event.

Mechanics of Evolution

• Mutation: the source of all new genetic variation.
• Natural Selection: increases the frequency of beneficial traits.
• Genetic Drift: random changes in allele frequencies.
• Gene Flow: movement of genes between populations.

Vestigial Structures

• Vestigial structures are remnants of organs or structures that had a function in an early ancestor.
• Have lost their function over time.
• Example: the human appendix.

Adaptive Radiation

• Adaptive radiation is the diversification of a group of organisms into forms filling different ecological niches.
• Often occurs when a species colonizes a new environment with few competitors.
• Example: Darwin's finches on the Galapagos Islands.

Divergent Evolution

• Divergent evolution is the process where groups from the same common ancestor evolve and accumulate differences, resulting in the formation of new species.
• May occur due to different environmental pressures.

Convergent Evolution

• Convergent evolution is the process where unrelated organisms independently evolve similarities when adapting to similar environments.
• Results in analogous structures.

Coevolution

• Coevolution is the process where two or more species reciprocally affect each other's evolution.
• Often seen in predator-prey relationships or mutualistic relationships.
• Example: flowering plants and their pollinators.

Bottleneck Effect

• The bottleneck effect is a sudden reduction in population size due to a random event.
• The surviving population has a reduced gene pool.
• Can lead to a loss of genetic variation.

Founder Effect

• The founder effect occurs when a small group of individuals separates from a larger population and establishes a new colony.
• The new colony has a reduced gene pool compared to the original population.
• Can lead to a higher frequency of certain rare alleles.