Let's imagine a post-scarcity society where everyone has unlimited access to food, energy and the aging problem has been solved so people are practically immortal.
Now my understanding is that, our brains have evolved in a way that maximizes our survival so our brains reward us for doing things that increases our survival chance (like eating, mating, seeking power and status to increase our security..etc) and discourage us from doing things that would decrease our survival chances. This is mainly done by secreting hormones like Dopamine, Oxytocin and Serotonin which make us want to repeat the beneficial action.
In my post-scarcity scenario, our survival will not be at risk since everyone is getting all the basic needs to stay alive and all the medical requirements to prevent death. Now, many many generations after us (millions of years), what will be those things that will make us feel happy or sad when evolution had stopped working on basis of survival?
In other words, what will be the purpose of future humans when survival is no longer the purpose? And if the purpose becomes to get as much happiness from life, then what might bring us this happiness and with what mechanism?