Humans ask questions like "where do we come from" and by nature we're very curious beings. Perhaps the flaw of a greater gift of possessing the will to question and learn, is the situation in which one attempts to prove if God does or doesn't exist and then leads to negative acts. Without our want to define and understand things I don't believe we'd be much beyond grunting and living in caves.(Although I know a few people who seem to prefer this lifestyle =D) Knowledge begins with a question. The answer to the next one I think would depend on the defined specifics of the situation. Some people wish to convince so they feel they are not alone in their beliefs, others do it for control, others do it to "enlighten" who they are speaking to because they believe they are corret on the subject. In my opinion, its as natural to us as breathing. If you thought you knew something and you were right, would you not wish to convince someone else of your belief? It seems the great minds of our race certainly did. Having evidence of one's belief can be a great help, in science its absolutely necessary, but in areas we cannot prove something totally, evidence will have a different interpretation to each individual.