Grandmother hypothesis: what is it and what does it propose about human evolution

The menopause process is often taken as something negative and, furthermore, from an evolutionary and survival point of view for the species it could seem counterproductive.

However, research has been carried out in this regard that has found a series of advantages for the survival of the species, given the important role that grandmothers play in caring for grandchildren.

The grandmother hypothesis is a theory that was developed 60 years ago in order to explain a series of benefits that menopause can have from an evolutionary perspective for humans and also for other species in which this process occurs, despite the fact that, as far as is known so far, there are very few species in which there is menopause.

Next we will explain what the grandmother hypothesis consists of and how it has developed, as well as what are the other species that, in addition to humans, go through the process of menopause.

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What is the grandmother hypothesis?

The grandmother's hypothesis is a hypothetical assumption that was developed in order to explain the role of menopause in humans, from an evolutionary and survival point of view of the species, since the females of the human species are among the few species that go through this process, along with some species of cetaceans (p. eg, the killer whale, the beluga, among others). After menopause, a process by which they stop ovulating and, therefore, being able to have more offspring, females of these species can live for decades.

That is why menopause is an unusual process in biology, since not even mammals that share the greatest kinship with the human species go through this process. Females of species in which the menopause process does not occur usually have a short life expectancy from the moment they can no longer reproduce, because their reproductive cycle is usually as long as their life expectancy.

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First statement of the grandmother hypothesis

In 1957, George C. Williams, an American biologist, developed a theory about menopause, postulating that this biological process that women go through between 45 and 55 years approximately supposes an adaptation for them, because, by living several more years, they could support their daughters and sons and help in the care of their grandchildren. This, taking into account that when the human being ages the probabilities of developing diseases increase and the years remaining lives decrease, and from an evolutionary point of view it would not be the most appropriate to have offspring at an age advanced.

Therefore, Williams postulated that elderly women can contribute to the transmission of their genes in the best possible way. helping their children and grandchildren to get ahead, instead of continuing to have children at an advanced age with the risks that would imply.

The Williams' grandmother hypothesis was made as a proposal to explain human survival throughout history, something that must be taken into account when understanding this theory, since at present this theory may be somewhat obsolete. However, in the days of hunter-gatherer groups, as well as in pre-industrial times, grandmothers could collaborate in the care of the grandchildren while their parents were hunting-gathering or, in later times, working.

It should be noted that this hypothesis has been developed from a biological and evolutionary perspective, given that today the way of life of our species has changed remarkably, since the means, the quality and the life expectancy have increased, so that even the fact of having children or not is a choice and not a necessity to survive as a species.

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Scientific support for the hypothesis

In the 90s of the 20th century, the North American anthropologist Kristen Hawkes investigated the importance of grandmothers in prehistory in favor of the evolution of the human species, postulating that the best way to perpetuate one's own genes and, therefore, that of the species, was supporting the daughters in the care of the grandchildren, so that they can get ahead with a greater probability of survive.

The grandmother hypothesis was investigated by Hawkes through the observations he made for more than a decade with families from the village of Hada (Tanzania), who lived by gathering food and hunting, a way of life similar to that of prehistory. During the study, they were able to observe the relevance of the fact that grandmothers they will collaborate in the collection of tubers when their grandchildren were not yet strong enough to do so themselves.

It must also be borne in mind that these hypotheses were focused on remote generations, so that seen this way, the grandmother could help collect food for the grandchildren so that they could be protected at home or take care of them while their mother and father They went in search of food, so this helped in the survival of the grandchildren and made it easier for their daughters to give them more grandchildren.

Based on this hypothesis, Hawkes states that increased longevity in humans was favored thanks to the help of the grandmothers in feeding the grandchildren who no longer needed breastfeedingIn a way, the grandmother was in charge of helping her in her care and feeding her while the mothers could have the following babies earlier.

In addition, this hypothesis is based on the conjecture that grandchildren may have a longer childhood that allows better development towards the stage adult thanks to the help of the grandmothers in taking care of her and in helping to collect food or any kind of help that they could offer to her family. However, criticism of this study has not been lacking, blaming a lack of statistical data.

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Animal species in which it is fulfilled

When Williams developed his research in relation to his hypothesis, it was only applied to the human being. Nevertheless, Later studies carried out by scientists from Canada and the United Kingdom were able to corroborate this hypothesis in other species, such as killer whales..

These studies document the benefits for the survival of the species when grandmothers no longer have the ability to have more offspring, being able to to verify that in those families in which the oldest killer whale had died, the grandchildren survived less frequently than those whose grandmothers were still with life. In addition, they were also able to verify that those older whales, which continued to have the ability to reproduce, did not provide the same support as those who had gone through the process of menopause who provided a greater support.

Other studies with the Asian elephant found that the females of this species with an older age, help in the protection for the survival of the grandchildren, despite the fact that they continue to reproduce.

These studies postulate that the period that grandmothers live after menopause, which is usually quite long, can last decades in the case of human beings. humans, it is very beneficial for increasing the longevity of both humans and killer whales, as grandmothers help in the survival of grandchildren remarkably, so that this remarkably compensates for the fact of not being able to have more children, all this always seen from a purely evolutionary point of view and from survival as a species