The 'Grandmother Hypothesis' - How Lola helps ensure the survival of her apos, but what about Lolo?

There is something called the “Grandmother Hypothesis,” according to which a “grandmother has a decidedly beneficial effect on the reproductive success of her children and the survival of her grandchildren” (Hawkes, 2004). It is hypothesized that the helpfulness of grandmothers is a consequence of menopause, and that menopause is an evolutionary adaptation. In the remote past, it is claimed, women who lived many years after they were no longer capable of bearing children could devote their energies to the rearing of their grandchildren and thereby enhanced these grandchildren’s possibility of survival. These grandchildren eventually parented daughters who also lived many years after they were no longer capable of bearing children... and so on until it became a genetic trait.

One expert writes, “Women... produce babies faster than otherwise expected because of grandmothers’ contribution to production. Grandmothers might affect the growth of infants in two ways: (i) by feeding nursing mothers and infants, thus accelerating the growth of infants, who then reach the size of independence more quickly, and (ii) by supplying food to weanlings, thus allowing infants to be weaned earlier” (Hawkes, 2004).

A 2004 Finnish study is claimed to provide empirical support to this idea (Lahdenperä, et al., 2004). The authors analyzed two 18th- and 19th-century populations and showed that in both of these populations the duration of a woman’s postmenopausal survival greatly affects the reproductive success of her children and the survival of her grandchildren. They write, “Grandchild survival to adulthood is enhanced by 12 percent when grandmothers are under 60 at their birth, but by only three percent when grandmothers are over this age. Grandmothers... have significant positive effects when offspring are between two and five..., and between five and 15...”

However, the Grandmother Hypothesis is not universally accepted by anthropologists, geneticists, and sociobiologists (see, e.g., Johnson, 2009). Some wonder whether it is not longevity that does the trick, and whether menopause is not just an artifact of longevity. Or, as one grandmother remarked after trying, unsuccessfully, to keep up with an overactive two-year old grandson, “No wonder Mother Nature invented menopause - people my age just can’t keep up with their own two-year olds anymore!”

Whoaaa - excuse us!!! What about the grandfathers? Why are Lolos completely excluded from this picture? As grandfathers who are fully involved in the upbringing of their grandchildren (together with the grandmothers, of course), we find this to be totally one-sided and completely dismissive of the role (OK, supporting role, maybe) of grandfathers in ensuring the survival and the development of their grandchildren.

We propose that a more even-handed, fairer, and probably even more politically correct proposition is to advance a “Grandparents Hypothesis,” which posits that “grandparents have a decidedly beneficial effect on the reproductive success of their children and the survival of their grandchildren.”

Besides, it is not just women who experience drastic changes in their reproductive capacity as they get older. There is such a thing as “andropause,” sort of the male equivalent of menopause. This is the slow but steady reduction of the production of the sex hormones, testosterone and dehydroepiadrosterone, that starts at around age 35 in men (Wikipedia, andropause, 2010). Freed from the hot passions of youth, Lolos can expend their energies chasing after their grandchildren, instead of chasing other love interests.

Further, the traditional role of the father is to provide for and to protect his family. During the hunter-gatherer years, it must have been very dangerous for a father to fulfill this obligation, especially the protection part, because of the many more lions and tigers and bears during that time in our evolution. The stress and dangers associated with this role almost certainly caused a more early demise of fathers, compared to mothers (something that we still see in these times). The presence of a youngish grandfather, who could take over the role of a departed father, would have contributed greatly to the survival of the offspring.

And then, there’s a Cambridge University study (Cambridge, 2010) that some grandmothers have more beneficial effects than others. The study shows that a grandmother’s effect on her grandchildren varies according to their X-chromosome relatedness. Maternal grandmothers are equally X-chromosome related to their granddaughters and grandsons. Paternal grandmothers, on the other hand, are X-chromosome related to their granddaughters but not to their grandsons. The study showed that while the presence of a maternal grandmother is beneficial to all her grandchildren, a paternal grandmother’s presence had a “harmful effect on her grandsons.” Not quite the expected “Grandmother Effect.”

Maybe the time has come for researchers to enlarge their agendas and start thinking about the “Grandfather Effect.” We should start in the Philippines, where “apostolic” work is a time-honored activity.

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References:

Hawkes, K. (2004), Nature 428:128-129.

Lahdenperä, M. et al., (2004), Nature 428:178-181.

Johnson, E. M. (2009), http://scienceblogs.com/primatediaries/2009/10/reply_to_moran_the_adaptive_va.php.

Wikipedia, andropause (2010), http://en.wikipedia.org/wiki/Andropause

Cambridge (2010), http://www.physorg.com/news176054402.html

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Alfonso M. Albano is Marion Reilly Professor Emeritus in the Department of Physics, Bryn Mawr College, Bryn Mawr, Pennsylvania, USA. He has three grandchildren and may be contacted at [email protected].

Eduardo A. Padlan is an adjunct professor in the Marine Science Institute, College of Science, University of the Philippines Diliman. He has five grandchildren and may be contacted at [email protected].