Foundations of Evolutionary Biology
What Evolution Explains
Core idea
Evolutionary biology studies how populations change over time through processes such as mutation, natural selection, genetic drift, gene flow, and recombination. A key shift from everyday intuition is that evolution acts on populations, not individuals, and it can produce both adaptation and non-adaptive change.
Central definition
Evolution is a change in allele frequencies across generations in a population.
Why the field matters
Evolution provides a unifying explanation for biodiversity, antibiotic resistance, viral emergence, crop improvement, conservation genetics, and the history of life. It connects molecular data, organismal traits, and ecological interactions.
Major levels of analysis
| Level | Examples |
|---|---|
| Molecular | DNA sequence change, protein evolution |
| Population | Allele frequencies, selection, drift |
| Species | Speciation, reproductive isolation |
| Macroevolution | Radiations, extinctions, major transitions |
Which statement best describes evolution in the modern biological sense?
Evolution refers to heritable change in populations across generations, not changes within a single individual.
Correct answer: Populations change in genetic composition over generations
What is the difference between an adaptation and a trait that is merely present in a population?
Not every trait is adaptive; some are neutral, byproducts, or historical leftovers.
Correct answer: An adaptation is a heritable trait shaped by natural selection because it increases fitness; a trait may be present without having been selected for that function.
Evidence for evolution
Fossils
- Show change through time
- Reveal transitional forms and extinction patterns
Molecular data
- Compare DNA and protein sequences
- Quantify relatedness and divergence times
Which type of evidence is most directly used to estimate relatedness between species by comparing inherited sequence similarity?
DNA and protein sequence comparisons are a primary source of phylogenetic evidence.
Correct answer: Molecular data
Study tip
When reasoning about evolution, always ask two questions: What varies? What process could make that variation more or less common over time?