Lecture Notes on Evolution and Natural Selection

Key Figures in Evolutionary Theory

• Charles Darwin

  • Known for the theory of natural selection.
  • Published "On the Origin of Species" in 1859.

• Alfred Russel Wallace

  • Independently developed the idea of natural selection.
  • Corresponded with Darwin, leading to a joint paper.
  • Often overlooked in favor of Darwin.

Concepts in Natural Selection

• Natural Selection

  • Traits that enhance survival and reproduction become more common in successive generations.
  • Based on heritable traits.

• Fitness

  • Measure of how well a genotype is represented in the next generation.
  • More fit organisms reproduce more, propagating their genes.

• Types of Natural Selection

  • Positive Selection: Favorable alleles.
  • Negative Selection: Harmful alleles.
  • Balancing Selection: Maintains diversity (e.g., sickle cell anemia provides malaria resistance).

• Patterns of Natural Selection

  • Stabilizing Selection: Selects against extremes (e.g., human birth weights).
  • Directional Selection: Shifts population traits in one direction (e.g., beak size in finches).
  • Disruptive Selection: Favors extremes (e.g., insect feeding habits change due to fruit availability).

Artificial Selection

• Humans selectively breed plants and animals (e.g., dog breeds, corn oil concentration).

Sexual Selection

• Intrasexual Selection: Competition among males for females.
• Intersexual Selection: Mate choice based on traits (e.g., colorful plumage in birds).

Genetic Drift

• Bottleneck Effect: Drastic reduction in population size.
• Founder Effect: Small group starts a new population, diverging genetically.

Speciation and Species Concepts

• Biological Species Concept (BSC)

  • Defines species based on reproductive isolation.

• Mechanisms of Reproductive Isolation

  • Prezygotic Barriers: Prevent mating or fertilization (e.g., behavioral, mechanical isolation).
  • Postzygotic Barriers: Affect the viability or fertility of the offspring.

• Types of Speciation

  • Allopatric Speciation: Geographic separation (e.g., isthmus of Panama forming).
  • Sympatric Speciation: Occurs within the same geographic area, often due to environmental pressures.

Modern Approaches to Studying Evolution

• Use of genomic techniques and molecular clocks to study evolutionary relationships.
• Phylogenetic trees to visualize evolutionary paths and speciation events.

Final Remarks

• Understanding of species and speciation continues to evolve with modern genetic insights.
• Differences in genetic flexibility between plants and animals, particularly in polyploidy.

Note: This summary covers the main points from the lecture on evolution, selection, and speciation, and prepares students for understanding the concepts of natural and artificial selection, sexual selection, and the factors that contribute to the diversity of life. Good luck on exams and future studies!