The importance of grandmothering to the developing of pair bonds

Who knew? Mark Prigg reports in Daily Mail,

'It looks like grandmothering was crucial to the development of pair bonds in humans,' says Kristen Hawkes, senior author of the new study published online in the Sept. 7 edition of the journal Proceedings of the National Academy of Sciences.

...Hawkes has used computer simulations to link grandmothering and longevity to a surplus of older fertile men and, in turn, to the male tendency to guard a female mate from the competition and form a 'pair bond' with her instead of mating with numerous partners.

...That conclusion contradicts the traditional view that pair bonding 'resulted from male hunters feeding females and their offspring in exchange for paternity of those kids so the males have descendants and pass on genes,' Hawkes says.

The grandma hypothesis holds that 'the key to why moms can have next babies sooner is not because of dad bringing home the bacon but because of grandma helping feed the weaned children.

That favored increased longevity as longer-lived grandmothers helped more.'

The new study focuses on the resulting excess of older males competing for mates, a likely source of men's preference for young women.

'This is different than what you see in chimpanzees, where males prefer older females,' says Hawkes, a distinguished professor of anthropology and National Academy of Sciences member.

As human longevity increased, there were 'lots more old guys, so you have an increasing number of males in the paternity competition, and the only way you can become a father is with a fertile female, which means younger females.

...The simulations showed how male-female sex ratios changed over time to become increasingly male-dominated - unlike real nonhuman great ape populations, which have more fertile females than fertile males.

...For example, the ratio of males to females in fertile ages rose from 77 males per 100 females without grandmothering to 156 males per 100 females with grandmothering in 30,000 to 300,000 simulated years.

Many anthropologists argue that increasing brain size in our ape-like ancestors was the major factor in humans developing lifespans different from apes.

But Hawkes' 2012 study ignored brain size, hunting and pair bonding, and showed that even a weak grandmother effect led to human longevity.

Indeed, she believes the shift to grandmothering was the foundation for several important steps in human evolution, including longer adult life spans, increased brain size, empathy, cooperation and pair bonding.

Read more here.
After reading this, I have questions. What percentage of grandmothers live in close proximity to their grandchildren nowadays in the United States? Is this study implying that men prefer younger women for some reason other than physical attractiveness? Like arguing that the reason men prefer younger women is because men want to pass on their genes and have descendants? Not because younger women are more attractive?