It’s not about thinking. Everything reproduces…organisms that don’t have the desire to reproduce don’t reproduce and thus their genes don’t get passed on. If a whole species stopped wanting to reproduce, they would be extinct in one generation. Only organisms that succeed in reproducing pass their genetic information to the next generation.
In fact, complicated brains and (and the social structures that require them) actually interfere with the genetic imperative for reproduction…allowing people to live entire, satisfied lives without passing their genetic information on (which is contrary to what their genes were designed for.)
One final point…sometimes we portray early humans as brutish…only caring about survival and sex with the men clubbing women and dragging them back to their caves. From what we can tell, early human societies were nothing like that. They were socially and culturally complicated. They had myths and culture and art and music and love and families just like we do.