Inbreeding is the mating of organisms closely related by ancestry, which goes against the biological aim of mating, which is the shuffling of DNA. In humans, inbreeding can lead to a high cost, such as an increased risk of genetic disorders and reduced fertility. Inbreeding can also be used to keep traits within a bloodline, as well as power, as seen in hereditary systems of rule such as the pharaohs of Ancient Egypt. Inbreeding is also used in breeding animals, such as mice used in lab experiments.
There are some families, such as the Whittakers in West Virginia, who are known to be heavily inbred. They have a long and complicated history of inbreeding, with early reports stating that the three siblings’ now-deceased mom and dad were brother and sister. The family later clarified that they were double first cousins — meaning that they share both sets of grandparents. The Whittakers are known to communicate only in grunts and bark at passersby. Another example is the "worlds most inbred family" in Australia, with four generations of incest, including at least 14 kids with parents all related to each other.
Inbreeding can lead to a host of side effects ranging from smaller adult size and reduced fertility to an increased risk of genetic disorders. The coefficient of inbreeding, or the degree of inbreeding in an individual, is an estimate of the percent of homozygous alleles in the overall genome. The more biologically related the parents are, the greater the coefficient of inbreeding, since their genomes have many similarities already.
