Contrast disruptive and stabilizing selections.
Disruptive selection refers to a type of natural selection that favors individuals at both extremes of a trait’s distribution while disfavoring individuals at the mean. Disruptive selection can create two distinct phenotypic groups and may lead to speciation.
Stabilizing selection, on the other hand, is a type of natural selection that favors individuals with intermediate traits while disfavoring individuals at both ends of a trait’s distribution. This type of selection acts to preserve the status quo and maintain the average phenotype in the population.
In summary, while disruptive selection drives the evolution of new phenotypic groups, stabilizing selection maintains the status quo by favoring individuals with average traits.
Disruptive selection and stabilizing selection are two types of natural selection that act on the traits of a population. Here's a step-by-step comparison of these two types of selection:
1. Definitions:
- Disruptive Selection: Disruptive selection occurs when extreme values of a trait are favored over intermediate values. This leads to the formation of two distinct phenotypic groups in a population.
- Stabilizing Selection: Stabilizing selection occurs when intermediate values of a trait are favored, while extreme values are selected against. This narrows the range of variation in a population.
2. Effect on trait distribution:
- Disruptive Selection: In disruptive selection, the extreme values of a trait become more common, while intermediate values become less common. This results in the formation of two distinct groups, each favoring one of the extreme phenotypes.
- Stabilizing Selection: In stabilizing selection, the intermediate values of a trait become more common, while extreme values become rarer. This leads to a reduction in the range of variation within a population.
3. Genetic diversity:
- Disruptive Selection: Disruptive selection can lead to an increase in genetic diversity within a population. The two distinct groups formed may have different sets of selected traits, resulting in increased genetic variation.
- Stabilizing Selection: Stabilizing selection tends to reduce genetic diversity in a population. As intermediate values of a trait are favored, there is a decrease in the frequency of rare alleles associated with extreme phenotypes.
4. Adaptive advantages:
- Disruptive Selection: Disruptive selection can lead to the evolution of new species or subspecies. The extreme phenotypes may be better adapted to different environmental conditions or exploit different resources.
- Stabilizing Selection: Stabilizing selection maintains the status quo and is often associated with stable environments. It favors traits that are well-suited to the current conditions, rather than pushing for rapid evolutionary change.
5. Examples:
- Disruptive Selection: An example of disruptive selection is the beak size in Darwin's finches. During periods of drought, seeds become harder, favoring larger beaks to crack them. However, during rainy periods, small seeds become abundant, favoring smaller beaks.
- Stabilizing Selection: An example of stabilizing selection is the birth weight of human infants. Extremely low birth weight and high birth weight infants have higher mortality rates compared to infants with intermediate birth weights.
In summary, disruptive selection favors extreme phenotypes, leading to the formation of distinct groups within a population, while stabilizing selection favors intermediate phenotypes, narrowing the range of variation. Disruptive selection increases genetic diversity and can lead to speciation, while stabilizing selection maintains the status quo in stable environments.