I like your post but have a criticism with his explanation for why people are not productive when depressed" "A lot of depressed people make statements like "I'm worthless", or "I'm scum" or "No one could ever love me", which are illogically dramatic and overly black and white, until you realize that these statements are merely interpretations of a feeling of "I'm about to get kicked out of the tribe, and therefore die."

I suspect that depression has multiple underlying causes depending on the individual.

Some examples:

1) Not everyone experiences depression when faced with failure, many don't, even if that failure would have meant getting kicked out of the tribe in the ancestral environment

2) mood disorders are more common in certain professions, ones where it would be erroneous to call unproductive. Suicidal ideation correates with divergent thinking and creative achievement in a sample of undergrads.

3) There is a new theory that depression in some may be due to mild brain damage, possibly caused by high fat diets, pollution, and lack of exercise. Evidence for this by its high percentage in industrialized society compared to egalitarian cultures, It is no surprise that high-dose, moderate intensity exercise alone works about as well as antidepressants.

4) Diseases such as diabetes and high-blood pressure can cause depression,due to its damaging effects on cognition.

I agree that these are good techniques to combat the fear of failure, and perhaps the source is fear of exile. But attributing depression as being rooted in tribal failure is a simplistic explanation based on the evidence available, and could give people wrong ideas on how to combat it.