Evolution Chapter: Natural Selection

Evolution

Natural Selection

• Process by which individuals with favorable traits are more likely to survive and reproduce
• Key components:
  • Variation in population: differences in traits among individuals
  • Heritability: traits are passed down from parents to offspring
  • Differential reproduction: individuals with favorable traits produce more offspring
• Types of natural selection:
  • Stabilizing selection: favors average traits
  • Directional selection: favors extreme traits
  • Disruptive selection: favors different traits in different environments

Fossil Record

• Chronological record of evolution through fossilized remains
• Provides evidence for:
  • Gradual changes in species over time
  • Transitional forms between different groups
  • Extinction events
• Fossil record limitations:
  • Fossilization is a rare process
  • Many species may not have fossilized remains

Adaptation

• Trait that enhances an individual's fitness in a specific environment
• Types of adaptation:
  • Structural adaptation: physical changes, e.g. development of wings
  • Physiological adaptation: changes in internal functions, e.g. increased oxygen efficiency
  • Behavioral adaptation: changes in behavior, e.g. migration patterns
• Adaptation vs. exaptation:
  • Adaptation: trait evolves for a specific purpose
  • Exaptation: trait evolves for one purpose, but is used for another

Genetic Drift

• Random change in allele frequency over time
• Causes:
  • Random sampling error
  • Genetic hitchhiking
  • Bottleneck effect
• Effects:
  • Loss of genetic variation
  • Fixation of alleles
  • Changes in population size

Speciation

• Process by which a new species emerges from an existing one
• Mechanisms:
  • Allopatric speciation: geographic isolation
  • Sympatric speciation: reproductive isolation within a population
  • Parapatric speciation: partial geographic isolation
• Types of speciation:
  • Adaptive radiation: rapid adaptation to new environments
  • Ecological speciation: adaptation to different ecological niches

Evolution

Natural Selection

• Favorable traits increase an individual's chance of survival and reproduction
• Variation in population is necessary for natural selection to occur
• Heritability of traits ensures that beneficial characteristics are passed down to offspring
• Differential reproduction leads to an increase in the frequency of favorable traits in a population

Fossil Record

• Fossil record provides a chronological history of evolution
• Fossils demonstrate gradual changes in species over time
• Transitional forms between different groups are found in the fossil record
• Fossil record is incomplete due to the rare process of fossilization
• Many species may not have left behind fossilized remains

Adaptation

• Adaptations are traits that enhance an individual's fitness in a specific environment
• Structural adaptations involve physical changes, such as the development of wings
• Physiological adaptations involve changes in internal functions, such as increased oxygen efficiency
• Behavioral adaptations involve changes in behavior, such as migration patterns
• Adaptations evolve for a specific purpose, whereas exaptations evolve for one purpose but are used for another

Genetic Drift

• Genetic drift is the random change in allele frequency over time
• Random sampling error, genetic hitchhiking, and bottleneck effect contribute to genetic drift
• Genetic drift leads to a loss of genetic variation, fixation of alleles, and changes in population size

Speciation

• Speciation is the process by which a new species emerges from an existing one
• Allopatric speciation occurs when a population is geographically isolated
• Sympatric speciation occurs when a population is reproductively isolated within a population
• Parapatric speciation occurs when a population is partially geographically isolated
• Adaptive radiation is a type of speciation that involves rapid adaptation to new environments
• Ecological speciation is a type of speciation that involves adaptation to different ecological niches