Gene Genie

I've been reading about mankind's great African exodus of 100,000 years ago. (Chris Stringer & Robin McKie : Amazon Link here ) Apparently at one point we as a species numbered around 10,000. Because of my outlook on life, I cannot help but wonder if it is this somewhat shallow gene pool that is the cause of such an escalation of mental and physical illnesses as we have progressed. Certainly our minds are finding new uses for all the raw emotional conditioning we gathered in the Rift Valley, but I cannot help but wonder whether because there were so few of us post-exodus, whether we ought to marry back into ancient African genes in order to get back any of the diversity we could truly realise. Genetically, Africa has the most diverse range of variation because of the amount of time mankind has spent there. I wonder how much depression there is on that continent amongst the indigenous peoples in comparison with the rest of the world?