Biology Chapter: Natural Selection

Heredity and Evolution

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.

Speciation

• 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.

Heredity and Evolution

Natural Selection

• 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.

Speciation

• 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.

Learn about the process of natural selection, including genetic variation and differential reproduction, and how it leads to the evolution of species. Understand the mechanisms behind this fundamental concept in biology.