The causes and the nature of genius are not well understood. Its varying appearances in a multitude of forms, throughout the human race, have led to much speculation and many theories about its origin and causes.

Once such theory, the biosocial theory of creativity, a very popular idea, suggests that there is a strong link between genius­ and insanity. Indeed, it suggests that genius is merely a special form of madness, and that the source of the genius abnormality lies in a physically defective brain, which is the result of hereditary coincidences (Mizrach). This theory gains support from many occurrences of close proximity between genius and insanity, as in the common portrayal of the mad scientist. Additionally, the hereditary nature of genius is exemplified by the many great composers in the Bach family.

Intelligence (and ingenuity) is often measured using a test to determine a person's intelligence quotient (IQ). Normal IQ scores range from 85 to about 115. IQs above 145 are generally considered to be genius, while scores over 200 are considered to be unmeasurable genius. Among those who may have had such IQs are Johann Wolfgang von Goethe, the poet and writer, and Gottfried Wilhelm von Leibniz, philosopher and mathematician (Norlinger).

The IQ test, as a means of determining intelligence, has received much criticism. This is primarily because intelligence can be of many different types, such as emotional, intrapersonal, or spiritual. It is difficult to strictly define something so varied and unpredictable as intelligence and genius. Indeed, many people are geniuses in ways that few tests can reflect. Additionally, because genius can be difficult to define, it is difficult to determine its causes.