Hair whorls on the head (parietal whorls) have been intensively studied because of the association indicated between brain development and abnormal hair whorls. (Both brain cells and skin cells are derived from an embryo's ectoderm tissue.) Abnormal hair whorls are used as a preliminary predictor of abnormal temperament in most domesticated animals, especially cows, but also in evaluating the mental status of apes and humans. A recent study found that homosexuals are more likely to have the less common counter-clockwise hair whorl phenotype than heterosexuals. Right and left handedness have also been linked to clockwise and counter-clockwise whorls, respectively.
Parietal whorls which are considered to be normal scalp patterns could be a single whorl or double whorls. Cases of triple parietal scalp whorls are less common but do not necessarily indicate abnormality. Abnormal brain development is usually indicated by the complete absence of hair whorls or abnormal placement of whorls on the scalp.