Describe the three types of selection: directional, stabilizing and disruptive and give an example of each

A directional selection is a mode of natural selection in which a single phenotype is favored, causing the allele frequency to continuously shift in one direction. Under directional selection, the advantageous allele increase in frequency independently of its dominance relative to other alleles; that is, even if the advantageous allele is recessive, it will eventually become fixed. It stands in contrast to balancing selection where selection may favor multiple alleles, and is the same as purifying selection which removes deleterious mutations from a population. For example smaller individuals and will, if the character is inherited, produce a decrease in average body size. 

A stabilizing selection is a type of natural selection in which genetic diversity decreases as the population stabilizes on a particular trait value. Stabilizing selection commonly uses negative selection to select against extreme values of the character. A example of this is human birth weight. Babies of low weight lose heat more quickly and get ill from infectious disease more easily, whereas babies of large body weight are more difficult to deliver through the pelvis.

A disruptive selection is changes in population genetics in which extreme values for a trait are favored over intermediate values. The variance of the trait increases and the population is divided into two distinct groups. The evolutionary process is believed to be the driving force behind sympatric speciation. For example if rabbits were put into an area that had very dark black rocks as well as very white colored stone, the rabbits with black fur would be able to hide from predators amongst the black rocks and the white furred rabbits would be able to hide in the white rocks, but the gray furred rabbits would stand out in both of the habitats and would suffer greater predation.