VESTIGIAL TWINS

A vestigial twin is a rare form of conjoined (Siamese) twinning or more accurately, of parasitic twinning, where the parasitic 'twin' is so malformed and incomplete that it simply consists of a couple of limbs or organs. The result is a normal person with – for example, an extra arm or leg attached to him or her.

This phenomenon occurs when a fertilised ovum or partially formed foetus splits. If the foetus splits completely, the result is two identical twins. However, if the foetus does not split fully, the result can be anything from two whole people joined by a bit of skin (conjoined / Siamese twins), through to one person with extra body parts: the extra parts are the body of the vestigial twin.

Most vestigial limbs are non-functional, and although they have bones, muscles and nerve endings, they are not under the control of the host. The possession of six or more digits on the hands and feet (polydactyly) usually has a genetic or chromosomal cause, and is not a case of vestigial twinning.

History

In centuries gone by, a person with a vestigial twin attached to him could expect any kind of reception from his peers - perhaps he would be burned at the stake as a witch or demon, or if he was lucky, he could appear in a freak show and earn some money.

Today

In developed countries, most people with vestigial twins or limbs choose to have them removed (or they are removed in infancy), and once this has been done, the host can live a life which is absolutely normal. Even before the removal of the extra limb or limbs, the vestigial twin is more inconvenient than dangerous.