Depression roots: What could be useful about depression?

Can you believe it? Depression has its good part, it's just the normal situation to adapt to the environment.
According to Science research, human beings revolutionized from simple animals to so complex specie, we can even think and have self-recognition.(Yea maybe God made human beings, let's just suppose evolution)
Each tiny character that risks our survival would cause our ancestors die. What left now, you and me, are highly complex animals and can adapt to the outside world perfectly.
Think about it, among our brains, only the most perfect brain will survive.
But why you still suffer from depression? Why our brain just suppress that feeling and left us happy and relaxed?
Now is the key part, the root of depression came.
Let's imagine the opposite first. Something that gets you low happens, you lost your job, you lost your girl friend or girl friends(:)).
No depression. You felt more happy than ever and relaxed than ever. You stayed in your house and watched TV and searched job offers in newspaper and listened to music and ate food and registered in other dating websites...
One year later, you finally found a job and you thought life was so wonderful.
The reality version:
In reality, you lost your job and your brain gave you a signal: Now start to feel depressed!
So you feel depressed. You have no mood of eating or searching dating websites, you just focused on searching for a new job, after one week, you found a job, but you still felt depressed and now you registered into the dating sites... or you called your ex girlfriends... whatever.
You got my drift right?
When you feel depressed or have any other negative feelings. Do you know the reason now?
Right, that's the signal given from our brain and told us to act now and change this situation so we could come back to our normal life.
In my later posts, I will continue with our journey to look deep into depression.

Leave you guys a question: Why only several people got such a depression syndrome that they could hardly conquer while the others can get out of that depressive mood and return to their normal lives? Here are some excellent and also hot sellers I recommend you to read, these ebooks are not directly concerned with depression, but would help you to learn more deep of depression.