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From the hunting hypothesis to the grandmother hypothesis: a short natural history of grandparenthood

13, Ottobre 2008 Inviato da Giovanni Ruggia in : attualità , trackback

I’ve become grandfather.
To celebrate this passage I went to look over the natural history of grandparenthood and discovered that the role of grandparents as helpers in the raising of kids could even date back to prehistoric times.
Today we think of the grandparent’s role as something new because we are used to seeing only the nuclear family, with a mother who takes upon herself the burden of the children’s upbringing and a father as the leader of the family. But it hasn’t always been that way. The demographical history, the evolution of the role of women and the factors that contribute to their reproductive success present a much more intriguing picture.

We usually believe today that there is a   general ageing of the population, but this is not the case. In past centuries as well, and even in ancient times, there were always relevant proportions of old people. The idea arises from mistaken interpretations of demographical statistics: there was a considerable increase of the mean life expectancy during the course of the centuries but this is due to the drastic fall of infant mortality. More that half of the infants died before coming of age, but once adults a good deal of them survived to see their grandchildren.
Even the belief that old people today are lone and deserted is a result of misinformation. There has been a real and relevant increase of the percentage of elderly people living on their own but this is true in every age sector and it should not be viewed as an evil. In the past centuries it was very common for elderly people to be alone because the children emigrated or were deceased, a situation due to poverty; today it is more a question of choice. To live well or badly one’s own old age is more a question of disposition and health than a financial one.

The role of women in prehistory has been systematically underrated. One must first of all get rid of the picture of heroic males hunting big game to bring home precious animal proteins. This is a traditional picture (the hunting hypothesis) that postulates a relationship between the long infancy of humans and the nuclear family. It assumes that a male/partner/father hunter has a decisive contribution in providing for his mate and his offspring. This hypothesis isn’t supported by any empirical evidence but, this notwithstanding, it remains popular even among scholars.
Humans differ from other primates in having a big but immature brain at birth, a long time of dependence after weaning, and a long postmenopausal period. These are evolutionarily correlated and linked to the consumption of highly nutritional food. There is no evidence, however, that meat was an important part of the diet during the evolution of hominids. Besides, it is very likely that meat came from the search of carcasses rather than from hunting proper.

In present day populations of hunters-gatherers the success of big game parties is rare (only in ~3% of the hunting days they catch some game). Furthermore, meat is shared among all the members of the group for reasons of social prestige, not only with one’s own mate and offspring. It is the female foraging, not male hunting, that secures the nutritional wellbeing of a family. Studies on present day hunter-gatherer populations have shown that women actively organize the foraging, looking for food that their children can’t obtain and prepare themselves, but can feed on. This evolved when resources easier to find and gather by infants began to run out because of changing ecological circumstances. This activity involves postmenopausal women as well. The help of these persons is particularly welcome when pregnant or lactating women have to reduce their foraging activity. The division of labour is then between mothers and grandmothers (the grandmother hypothesis) rather than between mothers and fathers. This suggests a solution to the enigma of human menopause: how come that in humans the period after menopause covers a significant part of the life arc, whereas in the remaining primates there is a decline of all the physiological functions parallel to that of fertility? In contributing to the reproductive succes of their daughters, women after menopause increase their own as well, in consequence an extension of life duration after the stop of the reproductive functions, deferring senescence, has been favoured by natural selection.

Between 50’000 and 40’000 years ago there has been a true explosion in the quantity and variety of artefacts, coupled with a demographic explosion of elderly people (four times more frequent). One of the most important discoveries in the last years is that the most often used tools by prehistoric people were cordages and textiles, rather than stone tools. One of their important uses, besides clothes and furnishing, was the construction of nets used for the hunting of small game like foxes and hares where all strata of the community, women, men, kids, elderly, took part.
In parallel with textiles a larger quantity of earthenware appeared together with dedicated craftspeople producing these materials, who judging by ethnographic research on extant populations, had to be women above all. The most skilled and talented of them enjoyed high status among these populations judging by the amount of scupted figurines in archeological relics, wearing knitted ritual decorations (headgears, gridles and the like), and who were shaped essentially as female figurines or “venuses”.

Among the primates there is considerable variation in reproductive success not only among males but also among females, lots of them not succeeding in begetting children and/or grandchildren to reproductive age, whereas others succeed in putting out almost all their generative potential. These differences in reproductive success are basically linked to the access to food resources – necessary for pregnancy and lactation – and to the ability of protecting their offspring from aggressions by other individuals of the same species. This is closely linked to the female’s hierarchical status. One of the basic principles controlling social organization of primates is the competition among females, in particular among their groups of descent. In these groups females with infants may count on the help of relatives in times critical for survival and reproductive success.
The expansion of the brain and cranium in humans causes further problems during delivery due to a pelvic girdle that has to be limited in size to allow walking in upright position. The problems of human females at the time of delivery make them to be the sole animals looking for and getting help during delivery: the midwife was likely to be the first job . The resource most at hand for this task were women that had already gained experience in delivery, that is to say, grandmothers.
The safety net is made up of countless relatives, not only elderly women after menopause – like grandmothers, but also not yet fertile adolescents– young aunts, that help mothers of their descent. This is documented in extant populations closer to the lifestyle of our hunter-gatherer ancestors: daughters can leave or stay (at least after the first marriage, they enter into several consecutive ones). Those who leave may come back if the marriage shouldn’t work out ( “I’m going back to my mother”, as Italian women use to say when quarrelling with their husband, it’s to be expression of a very old mood indeed). We don’t know how long couple bonds lasted in the Pleistocene but most likely they weren’t for life.
The woman’s situation worsened noticeably with the invention of agriculture, that paradoxically was initiated by women (whereas animal breeding, specially of big animals, is likely a male invention).
Agriculture brought about stable and larger settlements as well as a more sedentary life style. It induced negative consequences because of crowding and promiscuity with domesticated animals, thus worsening life conditions, malnutrition and infectious deseases. The ease of production of cereal based baby food shortened the birth intervals by speeding up weaning and decreasing the natural contraceptive effect of lactation. It is probable that the concept of private property arose as well, and with it the exploitation of labor of the weak, slavery, accumulation of big wealth, castes of warriors, and the erosion of gender equality.
With the development of civilization (agriculture, farming, commerce, industry, male line transfer of private property), women lost control over the resources needed for their own and their offspring’s survival and became in fact dependent on males. In addition, unlike most other primate species where the rule is that females stay with their birth group and males leave, in most human cultures the opposite occurs. It is the bride who moves to the husband’s family and this bereaves her of the solidarity and help she could get from her own family.

As any good hypothesis, the grandmother hypothesis as well produces some predictions that allow to verify it.
In pristine hunter-gatherer communities elderly women should prefer daughters to sons because they can’t be certain of the sons’ offspring, and indeed these communities are matrilocal, i.e. as a rule daughters stay and sons leave.
The grandmother hypothesis also predicts consequences on male mating strategies. If female fertility corresponds to the first part of the adult period of life, males should develop a preference for young women; a fact that is noticed in every human society indeed but not in other primate species. Yet an alternative explanation to this fact has been put forward which has nothing to do with menopause: the obsession with young women developed only in relation with patriarchy. During the Pleistocene period a young woman was not necessarily preferable; someone who had already proven to be able to carry a pregnancy to term could have been more interesting.
The grandmother hypothesis has also been tested with a mathematical model applied to the demography of the Aché, a hunter-gatherer population of Paraguay. The results have been little probatory, perhaps because of the limits of the mathematical model and of the complexity of the confounding factors.

I practically spoke only of grandmothers. So where do we leave the grandfathers? In primatological and ethnographical evidence they seem not to appear. Did they go hunting with their friends and not care about their grandchildren? If already fathers aren’t certain, fancy the grandfathers! In fact we know very little about grandfathers. Some current sociological data seem to point out that grandmothers are indeed more generous and reliable than grandfathers but when one has to do with human nature it is unlikely that researchers give simple and clear-cut answers. In the last some ten thousand or so years cultural evolution has arisen in addition to the biological one; human societies have altered the environments where they lived beyond recognition, they migrated and interacted intensely. The factors than come into play with human behavior are manifold, their interactions entangled, interactions between individuals unpredictable; rules of conduct are flexible and depend on context. Anyway grandmothers have taken the lead, it is in the power of grandfathers to follow in their tracks.

It isn’t said that the natural history of grandparenthood could help us realize where grandparents are bound for today – evolution produces change non-stop and thus novelty – there aren’t ultimate answers. But at least they can be assured that the emotions and feelings they feel towards their grandchildren and the role they feel to be able to take are the result of a long evolutionary history going back to the mists of time.


–    Pat Thane (ed.) The long history of old age. Thames&Hudson, London 2005
–    Sarah Blaffer Hrdy. Istinto materno. Sperling&Kupfer, Milano 2000 (ti orig. Mother nature, 1999)
–    Sarah Blaffer Hrdy. La donna che non si è evoluta: ipotesi di sociobiologia. Franco Angeli, Milano 1985
–    J.M. Adovasio, O. Soffer, J.Page. The invisible sex: uncovering the true roles of women in prehistory. Harper&Collins, New York 2007
–    Kim Hill & Ana Magdalena Hurtado. The evolution of premature reproductive senescence and menopause in human females: an evaluation of the “grandmother hypothesis”. in Laura Betzig (ed.). Human nature, a critical reader. Oxford univeristy press New York 1997
–    Kristen Hawkes, James O’Connel, Nicholas Blurton Jones, Helen Alvarez, Eric Charnov. The grandmother hypothesis and human evolution. In Lee Cronck, Napoleon Chagnon, William Irons (Eds)  . Adaptation and human behavior, an anthropological perspective. Aldine De Gruyter New York 2000
–    Robert Wright. The moral animal: why we are the way we are: the new science of evolutionary psychology. Pantheon books, New York 1994


1. Vinod Wadhawan - 5 Ottobre 2009

Mr. Giovanni Ruggia

I enjoyed reading your well-researched article. Your analysis confirms my suspicion that, as of now, grandfathers are pretty useless compared to grandmothers (unless they are rich!). This is particularly true for the prevailing conditions in India. But as you rightly state, evolutionary trends have been totally messed up by the highly complex processes of cultural evolution, as contrasted to the blind and purposeless processes of biological evolution. It is difficult to predict what things will be like even in the near future.

You mention the pelvic-girdle constraint imposed by the mother on the maximum size of the human skull and brain. I am reminded of Stephen Hawking. He was probably the first to articulate the view that this constraint would disappear when human embryos grow, not in the womb of the mother, but outside. Then we can evolve much bigger brains for ourselves. Among other things, that may also improve the relative importance of grandfathers, compared to grandmothers! This is just one example of what we humans are going to be doing in the near future, not to mention the huge possibilities that artificial evolution has in store for us (including superintelligent, post-biological, robots visualized by Hans Moravec and R. Kurzweil).