> Human being are just complicated ways for strings of nucleic acid to replicate themselves.

And from that evolved mechanisms for learning, consciousness, culture and technology. Amazing creative power in such a "small" task. I think the drive for survival is the root cause of all the other reinforcement signals that drive the brain development, such as the need for food, sex, sleep, companionship, learning and so on. Shaped under the influence of these reward systems, the brain evolves to create the subjective, intelligent and ineffable experience we all know we have but can't properly explain.