Grandmothers responsible for human longevity  Posted by Kate
Taylor  The helpfulness of grandmothers is the reason humans
don't die in their thirties the way chimpanzees do, new research
shows - and may even explain our bigger brains.  Computer
simulations show that with only a little grandmotherly care,
animals with chimpanzee lifespans evolve to reach a human level
in less than 60,000 years.  "Grandmothering was the initial step
toward making us who we are," says Kristen Hawkes of the
University of Utah.  The simulated creatures were given an
initial lifespan of 25 years from reaching adulthood. But after
24,000 to 60,000 years of grandmothers caring for grandchildren,
the creatures reaching adulthood lived another 49 years, just
like human hunter-gatherers.  The long-standing 'grandmother
hypothesis' says that when grandmothers help feed their
grandchildren after weaning, their daughters can produce more
children at shorter intervals. Thus, a few ancestral females who
lived long enough to become grandmothe