What is genius?

I recently read a theory that proposes that all people have the same basic mental capacity, and that the only differences are how that capacity is divided. The theory posits that normal people have a more equal distribution of capacity - think of brain capacity as a pie, divided into relatively equal pieces. Geniuses have an overly large portion of one or more parts of the pie. However, since we all have the same basic capacity, other portions of the whole would be reduced. It is commonly believed that people who are considered genius often have odd deficiencies in some behavioral or mental areas.

The equal capacity theory goes on to define idiot savants as individuals who have an abnormal abundance in one mental area, and therefore extreme deficiencies in many other areas. Such individuals can perform seemingly impossible mental tasks such as complex mathematics, but cannot tell time or remember to feed their dog. Below is a fascinating video about Stephen Wiltshire, which seems to demonstrate this interesting theory.