Compare and contrast directional selection and disruptive selection and provide an example of each

1. SIMILARITIES
Both directional and disruptive selection are types of natural selection. There are three types of natural selection, these are: stabilizing, directional and disruptive selections. Natural selection refers to the mechanism of organisms' evolution, which favor those that are more adapted to their environments. Such living organisms tend to live long, up to reproductive stage and give birth to many offspring. 

2. DIFFERENCES
Directional selection theory states that an extreme trait is always favored over other traits and this causes the allele frequency to shift over a period of time to favor the extreme trait. This implies that, a favored trait will be expressed as the most beneficial frequency in a population. The disruptive selection on the other hand is bimodial in nature and it favors two extreme traits in a population. This type of selection selects against the average individuals in the population by selecting traits at both extremes, thus leaving very few individuals in the middle. 

3. EXAMPLES
An example of directional selection is the length of the giraffe neck. Natural selection favored those giraffes, which have longer necks and can reach more food on high trees while those will shorter necks were wipe out, because they have restricted access to foods.
 An example of disruptive selection is the beak size of finches. The study on these birds was carried out by Darwin. He observed that, because the majority of seeds found in the environment of the birds were either large or small, both finches with large and small beaks were favored in that environment.