Noteworthy data is emerging to support the existence of longevity-enabling genes. Our observations of the relationship between reproductive fitness and longevity among centenarians support theories that posit strong selective forces in the determination of how fast humans age and their susceptibility to diseases associated with ageing. Current data support the idea that there is no selective advantage for humans to have a lifespan of approximately 100 years. Rather, getting to such a very old age may be a by-product of longevity-enabling genes that maximize the length of time during which women can bear children, and during which they can increase the survival probabilities of their children and grandchildren. We thus review the literature pertaining to the relationship between reproductive fitness and longevity.