Pair bonding traced to grandmothering…
A new study led by University of Utah anthropologist Kristen Hawkes known for her formulation of the “Grandmother Hypothesis” which ties extended human lifespan to prehistoric grandmothers who assumed the care of their grandchildren, credits them now for also paving the way for men and women forming pairs strengthened with sentimental bonds.
Hawkes had proposed the hypothesis during 1997-1998, basing it on her observations, starting in 1984, of the Hazda community in northern Tanzania who were living as hunter-gatherers like our prehistoric ancestors.
In her hypothesis which reverberated across the anthropological community, Hawkes pointed out that grandmothers helped feed their grandchildren by digging out tubers for them, taking on the burden from the mothers who could then have their second child earlier.
For Hawkes, this resulted in longer-living grandmothers transferring their longevity genes to larger numbers of people, thus lengthening the human lifespan, while at the same time reducing the burden tax of childbearing for women, allowing them to live decades longer after the end of their fertility unlike most mammals (see: “Granny’s Dear Will Live a Looong Life” https://kurious.ku.edu.tr/sites/kurious.ku.edu.tr/files/grandmothers_extended_human_lifespan_-_evolution_-_anthropology_-_pdf.pdf)
In the new study, Hawkes concentrates on the effects of increased male competition for younger (fertile) women brought about by the surplus of fertile older men due to the lengthened human lifespan. Whereas the women begin to use their ability to bear children, starting from the age of 45, men preserve their fertility for much longer.
As a result, the number of men competing for fertile young women to father children keep increasing and those who succeed are able to pass on their genes to descendants.
According to computer simulations made by Hawkes’ team, the ratio of fertile men and women, 77 men for every 100 women without “grandmothering”, goes up to 177 men to 100 women with grandmothering in projections from 30,000 to 300,000 years.
The thus increased ratio of fertile men to fertile women brings about the necessity of guarding mates against other suitors by pairing up and forging sentimental bonds, which provides an evolutionary advantage.
REFERENCES
- 1. “Did grandmas make people pair up?”, University of Utah, 7 September 2015