Biology Chapter: Natural Selection

Key concept: Natural selection is the process by which individuals with favorable traits are more likely to survive, reproduce, and pass those traits to their offspring.
Mechanisms:
- Variation: All populations exhibit genetic variation, which is the raw material for natural selection.
- Differential reproduction: Individuals with favorable traits produce more offspring, increasing the representation of those traits in the population.
- Heritability: Traits are inherited from parents to offspring, allowing natural selection to act on them.
Types of natural selection:
- Stabilizing selection: Favors average individuals, reducing variation.
- Directional selection: Favors individuals with extreme traits, increasing variation.
- Disruptive selection: Favors individuals with extreme traits, increasing variation.
Evidence for natural selection:
- Antibiotic resistance: Bacteria evolve resistance to antibiotics through natural selection.
- Pesticide resistance: Pests evolve resistance to pesticides through natural selection.

Definition: Speciation is the process by which a new species emerges from an existing one.
Mechanisms:
- Reproductive isolation: A population becomes reproductively isolated from the parent population, reducing gene flow.
- Genetic drift: Random genetic changes accumulate, leading to genetic differences between populations.
- Natural selection: Divergent selection pressures act on the isolated population, leading to adaptive differences.
Types of speciation:
- Allopatric speciation: Speciation occurs in geographically isolated populations.
- Sympatric speciation: Speciation occurs within a single population, often due to polyploidy or hybridization.
Evidence for speciation:
- Ring species: A series of interconnected species that form a "ring" around a geographic barrier.
- Fossil record: Transitional fossils and gradual changes in fossil records support speciation.

Favors survival and reproduction: Individuals with favorable traits are more likely to survive, reproduce, and pass those traits to their offspring.
Genetic variation: All populations exhibit genetic variation, which is the raw material for natural selection.
Differential reproduction: Individuals with favorable traits produce more offspring, increasing the representation of those traits in the population.
Heritability: Traits are inherited from parents to offspring, allowing natural selection to act on them.
Stabilizing selection: Favors average individuals, reducing variation.
Directional selection: Favors individuals with extreme traits, increasing variation.
Disruptive selection: Favors individuals with extreme traits, increasing variation.
Antibiotic resistance: Bacteria evolve resistance to antibiotics through natural selection.
Pesticide resistance: Pests evolve resistance to pesticides through natural selection.

Emergence of new species: Speciation is the process by which a new species emerges from an existing one.
Reproductive isolation: A population becomes reproductively isolated from the parent population, reducing gene flow.
Genetic drift: Random genetic changes accumulate, leading to genetic differences between populations.
Natural selection: Divergent selection pressures act on the isolated population, leading to adaptive differences.
Allopatric speciation: Speciation occurs in geographically isolated populations.
Sympatric speciation: Speciation occurs within a single population, often due to polyploidy or hybridization.
Ring species: A series of interconnected species that form a "ring" around a geographic barrier.
Fossil record: Transitional fossils and gradual changes in fossil records support speciation.