I don't know what partial comma is. But depression exists for evolutionary reason to conserve energy when we are sick, to limit the risky behaviours like movem

I don't know what partial comma is. But depression exists for evolutionary reason to conserve energy when we are sick, to limit the risky behaviours like movements (jumping from rock to rock, running after a wild buffalo) etc... But the problem is that the mechanism which can set us into depression can be tricked by our perception of the reality. What your eyes see and what you sense does not only depend on your eyes or your senses but also on how your brain interprets those. If your brain interprets a perfectly sunny day as warning for really long winter, your system can be tricked into sending yourself into depressive state. Now this can happen for variety of reasons like family problems, where you see your mom and dad hating each other while you were still developing at age 5, your brain development is affected and you sense more danger and pessimism than what a normal person would sense.