Sometimes called Diversifying selection. This type of selection favors both the extremes at the expense of the average.
An example of this is rabbits. In this example the rabbits have either black and white fur co-dominant genes, black fur represented by “B��? and white fur represented by “b��?. A rabbit with the genotype of “BB��? would have a phenotype of black fur, a genotype of “Bb��? would have gray fur (a display of both black and white) and a genotype of “bb��? would have a phenotype of white fur.
If this population of 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 thus would not survive.
If the very large and very small individuals in a population are favored and the average-sized individuals are selected against, this type of selection occurs.