Artificial vs. Natural Selection – Key Lecture Notes

Natural Selection and Evolutionary Processes

• Evolution comprises multiple mechanisms:
  • Natural selection
  • Genetic drift, gene flow, mutation, etc. (mentioned indirectly as “other processes”)
• Key distinction:
  • Only natural selection consistently produces adaptations to the environment that are passed on "in each succeeding generation."

Artificial Selection (Selective Breeding)

• Definition: Human-controlled breeding to increase the frequency of a desired trait in a population.
• Synonyms: Artificial selection = Selective breeding.
• Preconditions (shared with natural selection):
  • Requires genetic variation within the starting population.
  • Humans (rather than the environment) act as the selecting agent.

Classic Human Examples

• Domestic dogs: All modern breeds originated from selective breeding of wolves possessing particular traits—demonstrates the power of sustained artificial selection over time.
• Brassica oleraceae derivations:
  • Chinese cabbage
  • Brussels sprouts
  • Kohlrabi
  • (Broccoli and other cultivars also belong to this single species, though not explicitly listed in the clip.)
  • Illustrates that many dramatically different crop forms can trace back to one wild ancestor when breeders repeatedly favor distinct traits (leaf size, stem thickness, flower buds, etc.).

Darwin’s Insight & Broader Implication

• Observation: If humans can create vast diversity via artificial selection, nature could do the same through natural selection.
• Therefore, environmental conditions act as the selecting force in natural settings, replacing the breeder in artificial systems.
• Provides conceptual bridge from domestication data to Darwin’s theory of evolution by natural selection.

Natural Example—Galápagos Finches

• Famous case study highlighting natural selection:
  1. Initial population of finches colonizes the islands with genetic variation in beak morphology.
  2. Competition for limited resources leads to niche partitioning—different groups exploit different food sources.
  3. Birds with beaks better suited to cracking nuts preferentially survive and reproduce.
  4. These individuals repeatedly mate with each other, reinforcing specialized beak traits.
  5. Over evolutionary time, this divergence can culminate in a speciation event (new finch species with nut-cracking beaks).

Key Terminology Recap

• Adaptation: Heritable trait that increases fitness in a given environment; produced by natural selection.
• Niche partitioning: Process whereby competing species use the environment differently (e.g., food type, feeding time) to minimize direct competition.

Ethical / Practical Notes

• Artificial selection underlies modern agriculture, livestock, and pet breeding, raising questions about:
  • Biodiversity conservation (loss of rare alleles when breeders favor uniformity)
  • Animal welfare (selection for extreme traits may impair health)
  • Food security (monocultures vs. genetic resilience)

Numerical References & Future Course Context

• Upcoming deeper exploration of population-level evolution will continue in Chapter 16 and in the follow-up course BIO 102.

Transition

• End of the current chapter on natural vs. artificial selection.
• Next session will begin Chapter 16: “How Populations Evolve,” delving into population genetics, Hardy–Weinberg equilibrium, and evolutionary forces beyond natural selection.