Factors Affecting Evolution
This lesson covers:
- Factors affecting evolution
- How populations of different sizes are affected by evolution
- The bottleneck effect and the founder effect
What is evolution and what factors influence it?
Evolution is the process through which the inherited characteristics of a population change over generations. This change occurs as a result of variations in the frequency of different alleles within the population's gene pool. The gene pool is the complete set of genetic information in a population.
Several key factors influence evolution by altering allele frequencies:
- Mutation - Introduces new alleles and genetic variation.
- Gene flow - Involves the transfer of alleles between populations.
- Genetic drift - Causes random changes in allele frequencies, impacting small populations more significantly.
- Natural selection - Enhances the frequency of alleles that improve survival and reproductive success.
- Sexual selection - Increases the frequency of alleles that enhance reproductive success specifically.
Genetic drift
Genetic drift refers to the random changes in allele frequencies within a population's gene pool, due to chance events. Genetic drift does not occur as a result of natural selection.
It is particularly influential in small, isolated populations, where it can accelerate the development of new species.
Population genetics and natural selection
Population genetics examines the variation in allele frequencies over time, underpinning the concept of evolution.
The size of a population influences its genetic variation, which determines the potential for natural selection to occur.
| Population size | Genetic diversity | Adaptation capacity |
|---|---|---|
| Large | Large gene pools mean genetic diversity is high | They can adapt effectively to changing selection pressures through natural selection |
| Small | Small gene pools mean genetic diversity is low | They are at risk of extinction when there are changes in selection pressures |
The factors that can limit population size fall into two categories:
- Density-dependent factors - These depend on the size of the population, for example, competition, predation, and disease.
- Density-independent factors - These impact populations regardless of size, such as natural disasters and climate change.
The bottlenecks effect and the founder effect
The bottleneck effect and the founder effect are both scenarios that can greatly reduce a population size through different mechanisms.
The bottleneck effect
The bottleneck effect occurs when a population's size reduces suddenly and drastically and this reduction lasts for at least one generation.
Potential impacts of population bottlenecks:
- It leads to a reduced gene pool and decreased genetic diversity compared to the original population.
- The decreased genetic diversity can cause issues related to inbreeding and reduced fertility.
- However, it may also allow a beneficial mutation to become more prevalent.
The founder effect
The founder effect occurs when a small group splits from a larger population, and a small new population is established by this small number of individuals.
Potential impacts of the founder effect:
- It leads to a reduced gene pool and decreased genetic diversity compared to the original population.
- Rare alleles from the original population may become more common in the new population, whether they are beneficial, harmful, or neutral (an extreme example of genetic drift).