That's a misunderstanding of the thesis. Because humans tend to have trouble surviving completely alone, our nature is to privilege others and the group in many circumstances, over our individual wellbeing. Sacrifice - of comfort, health, even life - in order to secure the survival of our children and tribe is common because it is often so much more effective at allowing for the perpetuation of a given line than purely individualistic behavior. That's what's so profound about the concept presented in "The Selfish Gene": the meta-impulse to preserve one's genes often overrides the meta-impulse to preserve one's own life.