Look like a very few bubbas, living longer and helping mom raise the kids moved us from chimps to Justin Beiber! How is this relevant to marketing today?
Grandmas made humans live longer Oct. 23, 2012
The theory says that because a few older women among human ancestors began caring for their grandchildren, their daughters could have more children at shorter intervals, and that women ended up evolving long postmenopausal lifespans, unlike female apes who rarely survive past their childbearing years.
Computer simulations provide new mathematical support for the “grandmother hypothesis” — a famous theory that humans evolved longer adult lifespans than apes because grandmothers helped feed their grandchildren. “Grandmothering was the initial step toward making us who we are,”
The simulations indicate that with only a little bit of grandmothering — and without any assumptions about human brain size — animals with chimpanzee lifespans evolve in less than 60,000 years so they have a human lifespan. Female chimps rarely live past child-bearing years, usually into their 30s and sometimes their 40s. Human females often live decades past their child-bearing years.
The findings showed that from the time adulthood is reached, the simulated creatures lived another 25 years like chimps, yet after 24,000 to 60,000 years of grandmothers caring for grandchildren, the creatures who reached adulthood lived another 49 years — as do human hunter-gatherers.
The grandmother hypothesis says that when grandmothers help feed their grandchildren after weaning, their daughters can produce more children at shorter intervals; the children become younger at weaning but older when they first can feed themselves and when they reach adulthood; and women end up with postmenopausal lifespans just like ours.
By allowing their daughters to have more children, a few ancestral females who lived long enough to become grandmothers passed their longevity genes to more descendants, who had longer adult lifespans as a result.
But as human ancestors evolved in Africa during the past 2 million years, the environment changed, growing drier with more open grasslands and fewer forests — forests where newly weaned infants could collect and eat fleshy fruits on their own.
“So moms had two choices,” Hawkes says. “They could either follow the retreating forests, where foods were available that weaned infants could collect, or continue to feed the kids after the kids are weaned. That is a problem for mothers because it means you can’t have the next kid while you are occupied with this one.”
That opened a window for the few females whose childbearing years were ending — grandmothers — to step in and help, digging up potato-like tubers and cracking hard-shelled nuts in the increasingly arid environment. Those are tasks newly weaned apes and human ancestors couldn’t handle as infants.
The primates who stayed near food sources that newly weaned offspring could collect “are our great ape cousins. The ones that began to exploit resources little kids couldn’t handle, opened this window for grandmothering and eventually evolved into humans.”
Evidence that grandmothering increases grandchildren’s survival is seen in 19th and 20th century Europeans and Canadians, and in Hazda and some other African people.
The simulation begins with only 1 percent of women living to grandmother age and able to care for grandchildren, but by the end of the 24,000 to 60,000 simulated years, the results are similar to those seen in human hunter-gatherer populations: about 43 percent of adult women are grandmothers.
The new study found that from adulthood, additional years of life doubled from 25 years to 49 years over the simulated 24,000 to 60,000 years.
The difference in how fast the doubling occurred depends on different assumptions about how much a longer lifespan costs males: Living longer means males must put more energy and metabolism into maintaining their bodies longer, so they put less vigor into competing with other males over females during young adulthood.
What Came First: Bigger Brains or Grandmothering?
The competing “hunting hypothesis” holds that as resources dried up for human ancestors in Africa, hunting became better than foraging for finding food, and that led to natural selection for bigger brains capable of learning better hunting methods and clever use of hunting weapons. Women formed “pair bonds” with men who brought home meat.
Many anthropologists argue that increasing brain size in our ape-like ancestors was the major factor in humans developing lifespans different from apes. But the new computer simulation ignored brain size, hunting and pair bonding, and showed that even a weak grandmother effect can make the simulated creatures evolve from chimp-like longevity to human longevity.
So Hawkes believes the shift to longer adult lifespan caused by grandmothering “is what underlies subsequent important changes in human evolution, including increasing brain size.”
“If you are a chimpanzee, gorilla or orangutan baby, your mom is thinking about nothing but you,” she says. “But if you are a human baby, your mom has other kids she is worrying about, and that means now there is selection on you — which was not on any other apes — to much more actively engage her: ‘Mom! Pay attention to me!'”
“Grandmothering gave us the kind of upbringing that made us more dependent on each other socially and prone to engage each other’s attention,” she adds.
That, says Hawkes, gave rise to “a whole array of social capacities that are then the foundation for the evolution of other distinctly human traits, including pair bonding, bigger brains, learning new skills and our tendency for cooperation.”