Overview
This chapter explains the mechanisms of evolution, known as the "forces of evolution": mutation, genetic drift, gene flow, and natural selection, and describes how these forces change allele frequencies within populations over time.
The Modern Synthesis
- Modern Synthesis unified Darwin’s natural selection and Mendelian genetics into one theory of evolution.
- Darwin's and Mendel's ideas were previously considered incomplete alone.
- Experiments disproved Lamarckian inheritance (acquired traits are not inherited).
- Population genetics emerged, using mathematical models to study variation and allele frequency changes.
Populations, Genes, and Evolution
- A population is a group of interbreeding organisms of the same species.
- Species are defined by their ability to produce viable, fertile offspring.
- Populations can be divided into subpopulations (subspecies) with unique traits.
- Evolution is a change in allele frequencies in a population over generations.
- A gene pool encompasses all genetic material in a population.
Forces of Evolution
- Mutation is the original source of genetic variation, introducing new alleles.
- Only mutations in gametes (reproductive cells) are inherited by offspring.
- Point mutations, insertions, deletions, and chromosomal alterations are mutation types.
- Genetic drift is random change in allele frequencies, especially strong in small populations (bottlenecks, founder effect).
- Gene flow (admixture) is movement of alleles between populations, often through migration.
- Natural selection increases or decreases allele frequencies based on phenotypic advantages for survival or reproduction.
- Selection can be directional, stabilizing (balancing), or disruptive (diversifying).
Studying Evolution in Populations
- Hardy-Weinberg Equilibrium is used to estimate allele and genotype frequencies and detect evolutionary changes.
- Evolution can be studied by observing changes in these frequencies over time.
Microevolution, Macroevolution, and Speciation
- Microevolution involves changes within populations; macroevolution involves formation of new species.
- Speciation occurs through isolation (allopatric) or within the same area (sympatric).
- Adaptive radiation is rapid speciation filling various ecological niches.
Key Terms & Definitions
- Allele — A variant form of a gene.
- Gene pool — All genetic material in a population.
- Mutation — Change in the DNA sequence.
- Genetic drift — Random changes in allele frequencies.
- Gene flow — Movement of alleles between populations.
- Natural selection — Differential survival and reproduction due to phenotype.
- Hardy-Weinberg Equilibrium — Mathematical model for allele/genotype frequencies.
- Microevolution — Evolutionary changes within a species.
- Macroevolution — Large-scale evolutionary changes, such as speciation.
- Speciation — Formation of new species from a single population.
Action Items / Next Steps
- Review and practice Hardy-Weinberg calculations.
- Answer review questions on page 135 to reinforce understanding.
- Explore suggested further resources on evolution and human examples.