One might argue simply based on Maslow's hierarchy of needs that even a caveman would find better things to do if his needs for food, shelter, and sex were indubitably covered for life.

Maslow aside, learning could be argued to be the best way to ensure your own continued existence (unless you already decided your 'soul' is immortal). I'm not just talking about 'becoming immortal'; whether you lived centuries ago and learning about herbs or a snake could save your life, or you live in the present with the dangers of wasting away due to a lack of knowledge about the importance of diet, exercise, stress management, etc. Thus, to anyone who doesn't flinch away from the truth or escape thought altogether, our survival needs really aren't covered as well as they could be.