In Guns, Germs, and Steel, why did humans bother to leave Africa at all and go to such far away places as Australia and Americas? Did they decide it was time to colonize the whole world? Were they driven by curiosity about the unknown? Did the simply stumble and drift mindlessly from place to place? None of the above?
Of course, we have no way of knowing why people moved out of Africa. They left no records of their thoughts and there is no real method available to us that can tell us for sure why they left. We can only speculate. Using what Diamond tells us in the Prologue, I would speculate that people were motivated partly by curiosity. However, I would also say that it is most likely that the people did not consciously set out to discover the world. They were mostly moving without a great deal of purpose other than to find places with abundant resources.
The modern humans living in Africa could not have had any idea of the huge size of the world. They would not have had any feeling that they should go out and explore it. Their main thought was to survive. In order to survive, they would have moved about looking for places that had lots of food resources available to them. The search for such places would have led them further and further from their ancestral homes.
However, we can speculate that they had some curiosity. This can be seen from the fact that, as Diamond tells us on p. 41 in the paperback edition of the book, people only spread across the world after the “Great Leap Forward.” If something “turned on” in their brains that made them spread out, it might have been a greater sense of curiosity.