With the passage of time, more information was discovered about the natural selection, and its types. By the discovery of genetics, by the Mendel, the mechanism of natural selection became clearer, and now in the scientific community, it is accepted as the fact. Natural selection can occur in many forms. Some types of natural selection are stabilizing selection, directional selection, disruptive selection and sexual selection.
Stabilizing Selection
When the selection pressure is selected against the two extremes of a single trait, then the population experiences the stabilizing selection. The stabilizing selection may act on the plant height. The plant has a short height is not able to compete with other plants for getting the sunlight. However, the plants which are much tall, are more susceptible to the damage, caused by the wind. When these two selection pressures are combined, the stabilizing selection helps the plant to attain the medium height. Resultantly, the number of plants having the medium height will be increased and the number of tall and the short plants will be reduced.
Directional Selection
In this type of selection, the selection against the extreme trait distribution is observed. As a result, the trait distribution of the population is shifted towards the other extreme of that specific trait. Here the giraffe neck is the best example. They have undergone the selection pressure against the short necks. The individuals who had the short necks were not able to reach the leaves of the many trees, so, it was not possible for them to feed themselves. Then due to the redistribution of the length of the neck, they were shifted to the individuals with the longer necks.
Disruptive Selection
In this type of selection, the pressure actsed against the middle of the trait distributions. In this case, the median is not a favorable trait. It is favorable to have the one extreme or the other extreme, with the exception that there is no preference, which extreme will be better for survival. It is the rarest type of natural selection.
Sexual Selection
In this type of selection, the female species have to choose the mates, on the basis of the traits, which are found to be more attractive. Based on the attractiveness, the fitness of the males is judged. With more reproduction, more offspring will be produced and they will have more attractive traits.
