What is stabilising selection?

Stabilising selection refers to a type of natural selection that favors the average or intermediate phenotypes in a population, leading to a decrease in genetic diversity. This occurs because extreme traits are selected against, reducing the variety of phenotypes within the population. For example, in a species of birds where there is a selection for a specific range of body size, individuals that are too small or too large may be less fit for survival, thus making the intermediate size more prevalent over generations.

As a result, stabilising selection tends to maintain the status quo of a trait rather than introducing new variations or eliminating all forms of variability.