A hair whorl is a patch of hair growing in the opposite direction of the rest of the hair. Hair whorls occur in most hairy animals, on the body as well as on the head. Hair whorls, also known as crowns, swirls, trichoglyphs, or cowlicks, can be either clockwise or counterclockwise in direction of growth.
In human theories
Hair whorls on the head (parietal whorls) have been studied by some behaviorists. Most people have clockwise scalp hair-whorls. Parietal whorls which are considered to be normal scalp patterns could be a single whorl or double whorls. Cases of triple parietal whorls are less common but do not necessarily indicate abnormality.
Amar J. S. Klar conducted research to see if there was a genetic link between handedness and hair-whorl direction. He found that 8.4% of right handed people and 45% of left handed people have counterclockwise hair-whorls. His research indicates that a single gene may control both handedness and hair-whorl direction.
Another result concerning handedness of the progeny of discordant monozygotic twins suggests that lefties are one gene apart from righties. Together, these results suggest (1) that a single gene controls handedness, whorl orientation, and twin concordance and discordance and (2) that neuronal and visceral (internal organs) forms of bilateral asymmetry are coded by separate sets of genetic pathways. 
Animal behavioral theories
There are many (mostly apocryphal) theories concerning horse behavior and their hair whorls.
- Human handedness and scalp hair-whorl direction develop from a common genetic mechanism. Klar AJS Genetics 2003 Sep 165(1):269-76 http://www.genetics.org/cgi/reprint/165/1/269.pdf
- Forsberg Meyer, Jennifer. "What's in a Whorl?" Horse & Rider June 2008: 46-53.
- A note on hair whorl position and cattle temperament in the auction ring