Thanks for the introduction to the grandmother hypothesis I had never heard of it before, but it makes perfect sense. Nice piece Cadell.However, remember that although you probably expect to live into your 70s and 80s, most humans didn't have this luxury. Life expectancy in ancient times was closer to 30, and life expectancy in early 20th century America was only ~45. Improved nutrition, health care, and public sanitation over the past 100 years has gone a long way to improve the human condition.
Is this average from the 20th century of 45 because of infant mortality? If you were to take out the humans that died prior to the age of 18, what would that number look like? My guess is that we've gotten much better at keeping infants and children alive.