"If dreaming was selected for because of its adaptive function, the general content of dreams should certainly reflect this, and consist of situations that allow the rehearsal of scenarios that ultimately lead toward increased fitness. This is exactly what is seen, with studies indicating that dream content is biased toward negative elements reflecting threat, as opposed to positive elements. Data collected from over 500 dream reports by Hall and Van de Castle (1966) indicate that about 80% contained negative emotions, while only about 20% contained positive emotions. These negative dreams are also disproportionably likely to contain threatening elements such as animals and male strangers in threatening encounters. The evidence points towards the overrepresentation of threatening events in dreams, which should not occur if dream content is random. Through appropriating and learning to deal with these threats in dreams, it is proposed here that an animal could increase its overall evolutionary fitness."