Inbreeding Depression - in Humans

In Humans

Although severe inbreeding depression in humans seems to be highly uncommon and not widely known, there have been several cases of apparent forms of inbreeding depression in human populations. Charles Darwin, through numerous experiments, was one of the first scientists to demonstrate the effects of inbreeding depression. Darwin had married his first cousin, Emma Wedgwood. He later became concerned that inbreeding within his own family would adversely affect the health of his own children. The Darwins had ten children, but three died before the age of ten. Of the surviving children, three of the six who had long-term marriages did not have any children. As with animals, this phenomenon tends to occur in isolated, rural populations that are cut off to some degree from other areas of civilization.

A notable example is the Vadoma tribe of western Zimbabwe, many of whom carry the trait of having only two toes due to a small gene pool. Another example is Fumarase deficiency, a rare genetic disorder that leads to severe mental retardation. Over half of the known cases are in the isolated and adjoining polygamous Mormon communities of Hilldale, Utah and Colorado City, Arizona.