Microevolution
Change in allele frequencies within populations over short evolutionary time.
Microevolution refers to shifts in how common different versions of a gene are within a single population over time. These shifts are driven by four key mechanisms: mutation, selection (both natural and artificial), gene flow, and genetic drift. Compared to the larger-scale changes known as macroevolution, microevolution occurs over a relatively brief period. It supplies the fundamental changes that macroevolution builds upon.
The mathematical framework for studying microevolution comes from population genetics, while ecological genetics focuses on observing it in natural settings. Most directly observable examples of evolution, such as bacteria developing resistance to antibiotics, are instances of microevolution.
**Difference from macroevolution** Macroevolution operates by sorting differences between species ("species selection"), rather than sorting differences within a single species as microevolution does. Species selection can take two forms: effect-macroevolution, where traits of individual organisms (like body size) influence how fast species form or go extinct; and strict-sense species selection, where traits belonging to the species itself (such as its geographic range) affect those rates. Macroevolution does not create new evolutionary features, but it decides how widely those features spread within the groups where they first appeared. It also introduces species-level traits as non-organismal factors that influence this sorting process.
**Four processes**
**Mutation** Mutations are alterations to a cell's DNA sequence. They can be caused by radiation, viruses, mobile genetic elements (transposons), mutagenic chemicals, or mistakes during meiosis and DNA replication. Errors are especially common when the second strand of DNA is being built during replication. Some mutations are deliberately induced by the organism itself, for instance through a process called hypermutation. If a mutation occurs within a gene's protein-coding region, it can change the organism's physical traits. Error rates are typically very low—about one mistake per 10 to 100 million DNA bases—thanks to proofreading by DNA polymerases. Without proofreading, error rates are about a thousand times higher; many viruses, which rely on polymerases lacking this ability, therefore mutate much more frequently. Processes that increase DNA change rates are called mutagenic: mutagenic
- field
- Evolutionary biology
- known_for
- Change in allele frequencies within populations via mutation, selection, gene flow, and genetic drift
- key_processes
- Mutation, selection, gene flow, genetic drift
Lore & Background
Microevolution is studied through population genetics, which provides the mathematical structure for the process, and ecological genetics, which observes microevolution in the wild. Observable instances of evolution, such as bacterial strains with antibiotic resistance, are typically examples of microevolution. The four processes driving microevolution are mutation, selection (both natural and artificial), gene flow, and genetic drift. Mutation introduces changes in DNA sequences, which can be caused by radiation, viruses, transposons, mutagenic chemicals, or errors during meiosis or DNA replication. Selection acts on heritable traits that affect survival and reproductive success, making advantageous traits more common over generations. Genetic drift is the random change in allele frequencies due to random sampling, with larger effects in small populations. The relative importance of genetic drift versus natural selection is debated among scientists.
Reader's Guide
Microevolution is significant because it describes the fundamental mechanisms by which populations adapt to their environments over short timescales. It provides the raw material for macroevolution, which involves sorting of interspecific variation. Understanding microevolution is essential for fields such as medicine, where antibiotic resistance in bacteria evolves through these processes, and agriculture, where artificial selection shapes crops and livestock. The mathematical framework of population genetics allows precise modeling of how allele frequencies change under mutation, selection, gene flow, and drift. The distinction between microevolution and macroevolution is important: microevolution operates on intraspecific variation, while macroevolution involves species-level traits affecting speciation and extinction rates. The debate over the relative roles of natural selection and genetic drift continues, with some researchers emphasizing the neutral theory of molecular evolution. Microevolution remains a cornerstone of modern evolutionary biology, explaining both adaptive and non-adaptive changes in populations.
Did You Know?
- Microevolution provides the raw material for macroevolution.
- Observable instances of evolution, such as bacterial strains with antibiotic resistance, are typically examples of microevolution.
- The effect of genetic drift is larger in small populations and smaller in large populations.
- Mutations can involve large sections of DNA becoming duplicated, which is a major source of raw material for evolving new genes.
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