<P> Evolutionary psychology (or more specifically evolutionary psychopathology or psychiatry) has also been proposed as an overall theory, positing that many mental disorders involve the dysfunctional operation of mental modules adapted to ancestral physical or social environments but not necessarily to modern ones . Other theories suggest that mental illness could have evolutionary advantages for the species, including in enhancing creativity . Some related behavioral abnormalities have been found in non-human great apes . Evolutionary psychology applies Darwinian principles to human behavior by saying that human minds are products of natural selection and have specific functions . Humans strive to carry on their genetic legacy through their offspring . This theory identifies the environment as having a great effect on a person's mental development . </P> <P> Psychiatrists may favour biomedical models because they believe such models make their discipline seem more esteemed . Similarly, families of mentally ill people tend to favour biomedical models because to do so gives less self - blame . If patients are seen by a more ethnically similar doctor, they are more likely to adopt a non-biomedical model . </P> <P> Biological factors consist of anything physical that can cause adverse effects on a person's mental health . This includes genetics, prenatal damage, infections, exposure to toxins, brain defects or injuries, chemical imbalances, and substance abuse . Many professionals believe that the sole cause of mental disorders is based upon the biology of the brain and the nervous system . </P> <P> Mind mentions genetic factors, long - term physical health conditions, and head injuries or epilepsy (impacting on behaviour and mood) as factors that may possibly trigger an episode of mental illness . </P>

The two primary aspects of mood disorders are