6.2 Inbreeding

Inbreeding is a common phenomenon in nature, with countless populations using this as a method of reproduction as opposed to random mates. A major benefit of inbreeding is that it enables you to be more selective with certain traits, providing you with a smaller gene pool to select from. A major example of this can be seen in domesticated dog breeds. Although not natural, the ability to control inbreeding in dogs enables us to create specific breeds. By breeding two related dogs, it is almost guaranteed that the genetic diversity will be kept at a minimum, assuring the offspring has the desired traits. Also, it helps insure that a new dog will be a purebred rather than a mix with another breed. Assortative mating evolves to become more common as the gene pool decreases, causing an increase in preference to mates with similar phenotypes. 

While inbreeding poses the benefit stated above, it has more than its fair share of disadvantages that encourage avoidance of assortative mating. Inbreeding has a limited gene pool, which can have a negative impact on a species. This causes a limited amount of mates, and, if not enough potential mates are healthy, the population growth will experience a depression, threatening the existence. Also, especially within the human population, inbreeding can cause a number of birth defects. These include reduced fertility, a weakened immune system, and a significantly higher risk for genetic disorders. Because of these reasons, for many populations the negatives outweigh the positives of inbreeding, forcing evolution to lean towards dissassortative mating. 

Limiting the gene pool within a population through inbreeding is a risk and reward situation. While you may be able to have better control of the traits of the offspring, you also increase the chance that the offspring will not be as healthy or that future generations will not be able to reproduce as efficiently. It is dependent on the species for whether or not the risk of assortative mating is worth taking.