The Hollywood stereotype of inbreeding would have you believe it is a surefire route to being a horror villain. But what physical effect can it have on humans and animals, and how did it historically play a part in securing power?
What is inbreeding?
Inbreeding is the mating of organisms closely related by ancestry. It goes against the biological aim of mating, which is the shuffling of DNA. Human DNA is bundled into 23 pairs of chromosomes, within each chromosome there are hundreds of thousands of genes and what’s more, each gene has two copies known as alleles. Genes determine different aspects of your appearance, like hair and eye colour, as well as biological factors such as your blood type. These genes fall into two categories, dominant and recessive. If one of the genes in the pair is dominant, then the result is you gain the trait of the dominant gene. However, for traits that originate from the recessive gene, you need both genes to be recessive.
There is evidence that suggests inbreeding certain animals can have more of a negative impact than a positive one. The two largest populations of koalas in Australia could cease to exist by just one disease, due to them being so so heavily inbred, scientists have warned. A study, headed by Dr David Balding, examined inbreeding in pedigree dogs. Like the animals bred for farming, particular traits are encouraged in pedigree dogs, including their height and the quality of their fur. The study found that a large proportion of pedigree dogs suffered from conditions caused by recessive alleles such as heart disease, deafness and abnormal development of their hip joints. The problem is more alarming than it might seem on the surface. 20,000 pedigree boxer dogs would have the generic variety of around 70 dogs.
Incest isn’t entirely down to human interference and is part of the lifecycle of some animals. The reproductive patterns of Pyemotes boylei, a type of mite, are built around inbreeding. The mother mite keeps her eggs inside her until they reach maturity and the first wave to hatch is male. This incestuous vanguard waits outside their mother’s genital opening and as soon as the females hatch, their brothers impregnate them. Charming…
A limited gene pool in a species can, unsurprisingly, have a negative impact. This is known as Inbreeding Depression and refers to a population decrease due to lack of healthy mates. The problem can have a simple solution. Adders in Sweden were isolated due to farms and suffered an increase in stillbirths and offspring suffering from congenital defects. New adders were added and their population flourished. This is called outbreeding, for obvious reasons, and while it seems to be the go-to solution, there is a catch. Endangered species such as the Black Robin (Petroica traversi) have such small populations that there is no stock to replenish the population.
Inbreeding; perhaps best left to the mites. While it won’t automatically turn anyone into a Hollywood-style serial killer, it does leave your offspring at a greater risk of a whole host of congenital defects and genetic diseases.
Featured image © Abhishek Saini, EyeEm | Getty