Suicide risk is high at greater than 6% over 20 years, while self-harm occurs in 30–40% of those suffering from BD.
There are some scientists who now believe that Bipolar Disorder may have some evolutionary benefits and may actually be a result of evolution.
They argue that, if under severe stress or threat the depressive mood may serve as a defense strategy.
The depressed mood will force an individual to retreat from the stressor. He/she will also be inclined to sleep more which will preserve resources and energy for better times.
Mania, on the other hand, stimulates creativity, confidence, and high energy.
Evolutionary biologists have hypothesized that bipolar disorder could have come from an adaptation to extreme climactic conditions in the northern temperate zone.
Depression would have helped with survival during long winters because the increase of sleep, (similar to a mini-hibernation) lethargy, lack of interest in social activities and overeating would all have been conducive to winter survival.
The summers were short, so the hypomania would have increased energy levels, allowing for the completion of the many tasks necessary in a short period of time available, in preparation for winter.
