How did mankind become so obsessed with the belief in a god?

Well, research has pointed to genetics and with the discovery of epigenes, it seems plausible. It is possible that groups of humans that was formed around a common belief had evolutionary advantages over others, and after just a few generations the new program in the epigenes could have turned permanent. But how did it all start?

I am inclined to believe (just 'believe' since I am too lazy to research the matter) that the realization of our mortality was the trigger. Even today it is hard to accept the fact that we just die, that all our experiences and knowledge just vanishes when our organism seize to function.
Imagine what people would think of death thousands of years ago - maybe they thought that death was just another form of sleep, one that you woke up from in another world. And so the concept of a soul was born, and with it the image of what that other world would look like. Maybe as a way of comforting relatives, or a way of coping with everyday life, because if life has no meaning; what's the point of living it?

So, theism in its most original form had a function although it has been severely corrupted throughout the ages.