Going on the assumption that behavior are linked to genes, then genes would be able to be traced back through heredity, right?

But if that was really the case.. then how would you explain all the mental health problems? Take depression for example (non-situation depression that is). If you're depressed, then you have less likely of a chance to produce offspring, and less likely of a chance to pass your "depressed" genes down to someone else right? The whole survival of the fittest thing..

So then how can you account for how many people are depressed? Does that mean that behavior really doesn't have a lot to do with genetics? And if thats the case, then really, the whole genetic passing of mental health issues doesn't really make sense?

I'm not trying to offend anyone.. i struggle with depression myself... i'm just trying to scrap together some ideas.

Any thoughts?