Horror movies are, more often than not, poorly written bits of distraction that draw crowds looking for a quick scare. However, like most things, many common horror movie tropes contain a grain of truth. This is the first article in a series that looks at the scientific or medical basis for the defining features of several horror movie favorites.
First, let’s look at the werewolf. It is a monster of myth that is man by day, but a murderous wolf-creature by the light of a full moon. The tale of the wolf-man has a long history, being well established in Greek mythology. It should come as little surprise that hypertrichosis quickly acquired the nickname “werewolf syndrome”.
Did You Know?
Areas without wolves use other animals to fill the were-wolf role. Africa has "werehyenas", India has "weretigers" and South America has "werejaguars".
Generalized hypertrichosis is an exceedingly rare condition defined by an abundance of hair growth all over the body and is usually caused by one of two mechanisms. The first mechanism is defined by a conversion of vellushairs (short, non-pigmented hairs, sometimes called “peach fuzz”, which are typically found all over the body) to terminal hairs (larger and darker, like an adult male’s chest hair). It can also be caused by an increased length of the growth phase of the hair-growth cycle (which normally consists of growth, an end to growth and then shedding).
One cause of hypetrichosis is a mutation of the X chromosome. Men have one X and one Y chromosome, while women have two X chromosomes. We each receive half of our genetic material from our father and half from our mother. This means that a father with hypertrichosis will always pass it on to his daughters (who must inherit their father’s X chromosome and one of their mother’s two X chromosomes), but never to his sons (who must inherit his Y chromosome). A mother with the condition has a 50/50 chance of passing it on to a child of either sex.
Did You Know?
Localized hypertrichosis is a side effect of many common hair growth drugs.
The underlying causes and mechanisms of hypertrichosis have only recently been fully understood. It is easy to see how scientifically-primitive societies failed to understand hypertrichosis, which gave rise to the obvious comparison to the myth of the wolf-man.
The next installment of this series will cover those blood-sucking, coffin-dwellers we love to hate.
Wikipedia entry on hypertrichosis
Human genetics & gene inheritance
X-linked dominant father
X-linked dominant mother
Article first published March 17, 2011.