Overview
This lecture explains the true definition of biological evolution, clarifies common misconceptions, covers key mechanisms driving evolution, and reviews lines of evidence supporting the theory.
Misconceptions About Evolution
- In biology, individuals do not evolve; populations evolve over generations.
- "Fitness" in biology means reproductive success, not strength or health.
- Evolution does not always result in more complexity.
Biological Evolution: Definition and Mechanisms
- Biological evolution is a change in a population’s inherited traits across generations.
- A population is a group of organisms from the same species with varying traits due to genetic diversity (gene pool).
- Gene flow involves genes moving between populations, usually by migration.
- Mutations are random changes in genetic material and can be harmful, beneficial, or neutral.
- Genetic drift is a random change in gene frequency due to chance events.
- Natural selection favors individuals with traits that improve survival and reproduction, increasing their frequency over time.
Evidence for Evolution
- Homologies are similarities due to shared ancestry.
- Molecular homologies compare DNA, amino acids, or proteins to determine relatedness.
- Anatomical homologies are similar structures with a common origin but possibly different functions (e.g., human arm and dog forelimb).
- Vestigial structures are inherited but have lost most or all function (e.g., a claw on a chicken wing).
- Analogous structures have similar functions but evolved independently (e.g., bird wing vs. insect wing).
- Developmental homology examines similarities in embryonic stages among related organisms (e.g., notochord and pharyngeal slits in Chordata).
- The fossil record provides physical evidence of past organisms and shows changes over time; radiometric dating estimates the fossils' age.
- Biogeography studies the geographic distribution of organisms and how evolution explains patterns, taking into account continental drift and plate tectonics.
Evolution Is Ongoing
- Evolution is a continuous process observable in fast-reproducing organisms (e.g., antibiotic resistance in bacteria).
Key Terms & Definitions
- Population — A group of individuals of the same species living in a given area.
- Gene Pool — The total collection of genes within a population.
- Gene Flow — Movement of genes between populations.
- Mutation — A change in DNA sequence.
- Genetic Drift — Random changes in gene frequencies in a population.
- Natural Selection — Process where traits that improve survival become more common.
- Fitness (biological) — The ability to produce more offspring.
- Homology — Similarity due to shared ancestry.
- Vestigial Structure — Inherited structure that has lost most or all its function.
- Analogous Structure — Structures with similar function but different evolutionary origins.
- Biogeography — Study of species distribution in relation to geography.
Action Items / Next Steps
- Watch the videos on natural selection and speciation for deeper understanding.
- Review textbook sections on mechanisms of evolution and evidence for evolution.