Answer: whatever you want it to be.
Step-by-step explanation:
There isn't a clear answer for good reason. Think back to jesus stuff about adam and eve and the place they lived in (eden, was it called) Before there was any (wsdom) people did whatever they wanted, ran around no clothes on and ate and played or whatevere. they just did what they wanted. There's the whole story of how there was a knowledge apple or whatever, and humans built their society (their own) to thrive. They thrived to keep living. In short, the reason we exist is whatever you want the reason to be. Y'know what they say, You choose your own destiny