Hypertrichosis
Many feral children are reported as being covered with body hair when found, which eventually disappears after they are returned to civilisation. Indeed, Linnaeus' definition of feral children (homo ferus) was that they were "hirsutus" (hairy), even though not all the children on Linnaeus' list (which errs in several other ways) were in fact hairy on discovery.
Caucau
Hairy children
Children who were reported as being hairy when found include CauCau, Jean de Liège, Goongi, the wolf-boys of Shahjehanpur, Kronstadt and Hasunpur, and John Ssebunya.
Malnutrition
We are unfortunately all too familiar with the sight of badly-nourished children in famine areas, and they quite clearly aren't hairy. But feral children suffer a very peculiar kind of dietary deficiency. They do eat enough to keep alive, but it's a diet that is very skewed to one or at most two food groups. Living with wolves, they eat raw meat and nothing but. In isolation, most eat plant material only.
If malnutrition of some type is the cause of hairy feral children, the exact mechanism will be due to the malfunction of a hormone production area: the adrenal gland, the thyroid or the ovaries.
Explanations
Descriptions of hairy children have understandably been responsible for casting doubts on the veracity of reports of feral children. There are three possible explanations for this bizarre phenomena.
1: Somebody made it up
One explanation is that someone made up these stories in their entirety and embellished them with hairiness, or invented the fact that the children were hairy. This doesn't seem likely, as the result of adding this implausible characteristic would simply be to make the stories less credible.
However, it is interesting to note that there are no photographs of feral children covered in hair.
2: The children weren't hairy
An alternative possibility is that the children were very dirty, and that this looked like hair. Feral children would be filthy indeed. And although they were supposedly impervious to cold, it's difficult to imagine Victor, for example, going to much trouble to keep clean using the ice-cold water available to him in that bitter winter of 1799/1800. But these children were caught only with some difficulty, and had to be physically manhandled. No one that close to them could have mistaken dirt for hair.
3: Hypertrichosis
There is a condition which does cause hair to grow all over the body. Known as hypertrichosis, it can be caused by a number of factors, including two that are likely to be relevant: malnutrition and untreated infection. Of these, malnutrition seems to be the most likely explanation (hypertrichosis is a common symptom of anorexia nervosa), although both are possible causes in feral children.
Digby, Two Treatises…
