Overview
This lecture defines biological evolution, explains its mechanisms, and describes the main lines of evidence supporting evolution, including homologies, the fossil record, and biogeography.
Biological Evolution: Definitions and Misconceptions
- Evolution in biology is a change in a population’s inherited traits over generations.
- Individuals do not evolve; only populations evolve.
- Biological fitness refers to reproductive success, not physical strength.
- Evolution does not always result in increased complexity.
Mechanisms of Evolution
- Gene flow: Movement of genes between populations, often via migration.
- Mutations: Random changes in genetic material that introduce variation.
- Genetic drift: Random events change gene frequencies in small populations.
- Natural selection: Traits that improve survival and reproduction become more common.
Evidence for Evolution
Homology
- Molecular homology: Similar DNA, amino acids, or proteins indicate shared ancestry.
- Anatomical homology: Homologous structures have similar form due to common ancestry but may serve different functions.
- Analogous structures: Similar function but not structure or ancestry (e.g., insect and bird wings).
- Vestigial structures: Inherited from ancestors but typically nonfunctional (e.g., chicken wing claw).
- Developmental homology: Similar embryonic development stages (e.g., notochord, pharyngeal slits in Chordata) show shared ancestry.
Fossil Record
- Fossils are remains or traces of organisms from the past.
- Fossils reveal changes in populations over time and provide insight into ancestral organisms.
- Radiometric dating estimates fossil ages using radioactive decay.
Biogeography
- Studies geographic distribution of organisms to show evolutionary patterns.
- Island populations often show unique traits due to independent evolution.
- Closest relatives are usually geographically nearest, reflecting shared ancestry and past continental connections.
Evolution Is Ongoing
- Evolution continues as populations change across generations.
- Rapid evolution is observable in short-lived organisms, such as bacteria developing antibiotic resistance.
Key Terms & Definitions
- Biological evolution — Genetic change in a population across generations.
- Population — Group of the same species living in an area.
- Gene flow — Exchange of genes between populations.
- Mutation — Change in DNA sequence.
- Genetic drift — Random shifts in gene frequencies.
- Natural selection — Process where advantageous traits increase in a population.
- Fitness (biology) — Reproductive success.
- Homology — Similarity from shared ancestry.
- Analogous structures — Similar function, different ancestry.
- Vestigial structures — Inherited but mostly nonfunctional features.
- Fossil — Preserved remains or traces of past life.
Action Items / Next Steps
- Watch the Amoeba Sisters’ videos on speciation and natural selection for further learning.