Yes indeed but some you mention were manic-depressive, what we now call bi-polar. Sylvia Plath for example, and she did top herself poor soul. Still you are right, it's not nice to live through though. Someone above said the good thing was depression does go eventually but it can last a very long time, with occasional brief respite, and it seems like a lifetime.
I know someone very well, a talented musician and a computer programmer, who has a diagnosis of bi-polar and manages it quite well without medication (some of the meds make everything worse unfortunately). This person has great insight and many friends. One big difficulty is with relationships, they have had a couple of long term ones, one particularly lasted more than eight years, but it was difficult. No animosity, they still have a high regard for eachother and are friends but living together became impossible. You can imagine, when one has been working non stop and then wants to do nothing except stay in bed for days and the other would like to go out or on holiday, it's not a good scene.
Ah well, enough of this depressive talk.
I sincerely hope no-one does isolate the 'depressive gene', and get rid of it, it would do great damage and set a precedent for other things.