SCIENCE JANUARY 29, 2013 Why do grandmothers exist? The question
is not as unfeeling as it sounds. From the point of view of the
selfish gene, creatures are supposed to drop dead as soon as
they lose the power to reproduce. A man can make babies his
whole life, even if the sperm of his old age lacks vigor and
genetic fidelity. A woman outlives her eggs by about 20 years,
which almost no other female mammals do.1 (Only female killer
and pilot whales and orcas are known to last as long after the
end of their menstrual cycles.) Besides being classed among the
oddities of the animal kingdom, post-menopausal women lack
obvious utility. They tend to be weak. They don't have much sex
appeal. They eat food working people might make better use of.
In Paraguay's Ache tribe, aging women used to listen with terror
for the footsteps of the young men whose job it was to sneak up
on them with an ax and brain them. Most societies don't actually
murder their grannies, but that women manage to attain old age
is an evolutionary