In year 1957, the biologist George Williams proposed the new theory, popularly called “stopping-early” hypothesis, he claims in his hypothesis that women in her forties need some time without new babies to guide their other children into adulthood. In the middle of 1980s, American anthropologist Kristen Hawkes and cultural ecologist James Francis O’Connell spent few years with Hadza tribe in Tanzania, the last known hunter-gatherers in Africa, she also analyzed studies of hunter gatherers in Papua New Guinea and Gambia. From these studies we can see why grandmothers are so important in today’s society. A fundamental factor that favored the continued existence, growth and flourishing of our ancestors was the key contribution of maternal grandmothers. Among evolutionary biologists and anthropologist, the “grandmother hypothesis” is the most broadly known explanation for human post-reproductive long life. This theory suggests that healthy, capable, elderly women are able to contribute to their grandchildren’s survival through nutritional provisioning because she shares one quarter of her genes with a grandchild (Hawkes et al. 1998; Fox 2009).
According to Bernstein Kuhle (2007) origin of menopause it often falls into two dissimilar categories, the first one is “adaptationist hypotheses” and the second is “byproduct hypotheses”. “Adaptationist hypotheses” see menopause as a characteristic which is naturally selected helping increase our ancestor’s reproductive success. “Byproduct hypotheses” on the other hand say the opposite to the adaptationist hypotheses. The “byproduct hypotheses” doesn’t view menopause as something reproductively positive, they see a menopause as a byproduct or side affect of many other distinctiveness or occurrences. Of course, many authors have theorized that menopause is a side effect of selective pressure to increase female life expectancy, and one of the most important and most well known theory is “grandmother hypothesis” (Hill & Hurtado 1991; Sherman P W 1998; Kuhle, 2007 ).
The phenomenon why women live long past the age of child-bearing it’s not something new, and against common belief their purpose is not due to support the elderly. According to the “grandmother hypothesis” grandmothers have a lot to offer their grandkids, grandmother have beneficial effect on the survival of her grandchildren. The existence of post–generative longevity and menopause as normal part of the life history of females, and it is always have been a little bit mystifying from an evolutionary and scientific perspective (Hill & Hurtado 1991; Sherman P W 1998, Hawkes 2003; Grainger 2004;).
Fertility rises slowly with age of the woman, usually hit the highest point in the late twenties or early thirties, and then slowly fall in late forties or early fifties. Once it has reached this point it becomes impossible for women to have children anymore; however women can expect to live more than twenty years after menopause, even in modern hunter-gatherer societies without contemporary medicine (Finch and Gosden, 1986; Gage, 1998; Harley, 1990; Hill & Hurtado 1991; Bellino and Wise 2003).
According to Richard Dawkins (1997) and his theory about the “selfish gene” humans are supposed to die as soon as they lose the ability to have child bear. In the past such as the Pleistocene or even the early nineteenth century scientists argued that women did not live past menopause. Before modern hygiene and medicine, people did not live that long compared life after their introduction. Today however a large number of scientist do not believe that. Although, it is true that in past times people usually did not reach certain ages but that does not have a direct link with fertility. Around the same time children were known to die at a tragic young age keeping life-expectancy averages very low. However, humans still had the ability to live twice as long as our hominid relatives. Those who reached the age of 15 had about a 70% chance of making it to forties or even fifties, at which point odds there was an even better chance of them making it to an older age. Today, many anthropologists and biologists believe that the bodies of human are designed to last about 72 years (Pavelka et al. 1991).
According to Iniko Uujama (2012), for many years, biological anthropologists and evolutionary biologists have tried to give explanation why menopause exists, and why is a menopause one and only life stage that humans do not share with our primate relatives (Washburn, 1981; Weiss, 1981). An anthropologist at the University of Utah Kristen Hawkes suggested a theory in which she explained menopause by citing the under-appreciated evolutionary significance of grand mothering (Hawkes et al. 1998; Fox 2009). Hawkes claimed that grand mothering isn’t just a role carried out by a family member. She saw it as a key component in helping us to build up “a whole array of social capacities that are then the foundation for the evolution of other distinctly human traits, including pair bonding, bigger brains, learning new skills and our tendency for cooperation” (Hawkes, 1998)
In her works a Kristen Hawkes (1998) claim that is important to know that “grandmother hypothesis is not a theory for the evolution of menopause but a theory for continued longevity after menopause”. According to the hypothesis, grandmothers can help gather food and nourish the children before the ages that they are capable to feed themselves, by doing this it allows mothers to concentrate on having more children (Hawkes et al. 1998; Fox 2009). Without grandmothers, if a mother have a new baby and already has a very young child, the odds of that child surviving are not good, because unlike other primates, humans aren’t able to feed and take care of themselves right away after breast feeding (Finch and Gosden, 1986; Gage, 1998; Harley, 1990; Hill & Hurtado 1991; Bellino and Wise 2003).
According to Hawkes (2003) observations among Hadza hunter–gatherers in Africa may give us a very nice explanation for our evolutionary longevity. By looking at the link between foraging patterns of the youth and their mother’s and grandmother’s, it gives us a good insight for inherited past. This also includes a reproductive position for older females and consequently a shift in the rates of aging. Children of a young age are not always the most effective gathers and sometimes lack the strength because the relay large and heavy root of a plant is buried deep in the ground and needs some strength to dig out. A Senior Hadza woman, who is more experienced in gathering, can spend extra time with her grandchildren helping them in a gathering. In doing this she is making an important contribution to the dietary needs of their grandchildren, which is important because kids cannot accomplish for themselves. Young members of the tribe frequently depend on the foraging effort of their mothers. However when their mothers have a newborn baby in the house, the young Hadza children dietary wellbeing mostly depends on the effort of their grandmothers or other members of the tribe. Hawkes in her first book (1989) speculated that this is a “strategy designed to reduce the workload of related family connections allowing them more time to focus their efforts on reproducing” (Hawkes 2003; Grainger 2004;).
The grandmother theory simply suggests that women who are too old for having babies helps not just their children, but their grandchildern, and by doing this helps extend the human existence in the process. Without their own responsibilities of a baby grandmothers had both time and an excellent reason to be useful to their daughters. When they find food and other nutrition’s for children of their daughters, they almost certainly reduce the chance that those young children dying from hunger. As a consequence, that gave the grandmothers a better chance of passing on their own predisposition to long life (Hawkes 2003; Grainger 2004).
The grandmother hypothesis also explains another mystery “Why do humans have shorter birth intervals than other primates?” When looking at chimp mothers our closest living relatives, we see that they will often wait 5 or even 6 years until they look to reproduce again. Although not immediately, human reproduce at around 6 weeks after having an infant. It seems to be the case that once humans had learnt the art of mutual or shared child-rearing, grandmothers started to spend more time with and developing their grandchildren. This leads to women being more confident in having and being stable with more than one child. When chimpanzee infants stop to drinking their mothers’ milk, they become nutritionally independent and they can feed themselves. Compare that to the life of a human. Even though human children can be amazingly smart and successful foragers at a very young age they continue to depend on others to supply considerable fractions of food and knowledge of life (Flatz & Rotthauwe 1973; Jacobson 2013).
As the grandmother effect spread all the way through the population over thousands of generations, it also evolved humans in another way. It made their brains much bigger. As life extended, so did each stage of it. Children stayed children for much longer, a very important stage in life. It is during this stage where their brains are able to develop much better and they became stronger than previous generations (Hawkes 2003; Grainger 2004).
Another new dimension was added with the introduction of increased food-sharing. This allowed mothers and the young children accompanying them to remain in their own habitats they otherwise could not and to settle in new previously unexploited habitats. But the feeding of this children, would certainly delay a mother’s new child. Leading to an excellent opportunity for the older females whose declining fertility made them less probable to have a baby of their own: feeding their just old enough grandchildren would allow their daughters to have shorter afterbirth intervals, again reiterating the fact they could have more children (Hawkes 2003; Grainger 2004).
When summarizing the “grandmother hypothesis” it’s important to say that it proposes that life of the woman after menopause is not simply a result of mankind’s achievement in postponing death through medical progress and huge changes in lifestyle. But it is also that they continued to help in raising grandkids and helping their daughters. The “grandmother effect” has led to more numerous and developed roles of the grandmother. Primarily, grandmothers’ prolonged their life and capability to help their children after they are no longer capable of reproducing. Second, non-human species, in our case chimpanzees, do not stay with their daughters to watch out for grandkids (Jacobson, 2013).
Supporters of this thesis, Shanley and Kirkwood (2002), showed that while risk are bigger for maternal mortality with an escalating age alongside the requiring nourishment of human babies is not adequate to explain the existence of menopause. If post reproductive women also reduce their grandchildren mortality by more than ten per cent, and increase their daughters’ fertility by thirteen per cent, then women who are in menopause have greater reproductive health than those who are not (Shanley and Kirkwood 2002, Hawkes 2008).
According to Roni Jacobson (2013) Primatologists have observed for more than a ten years that chimpanzees usually move to another place when they achieve their sexual maturity. Although the moving of sexual mature chimpanzees is not obligatory, sexually mature female chimpanzees and their mothers frequently live in different places, not giving the chance for grandmother chimps to help nurture their grandchildren. A large and widespread disparagement of the “grandmother” theory has been that there is no mathematical proof of how sporadic grandmothering could have moved us from chimp-like life length to a human one. Roni Jacobson goes further in his claims when he said that grandmothers are not the only ones in tribes who provide support to a mum and grandchildren. Among the Hadza families from Hawkes study, only four of the eight cases she counted as grand mothering” came from real grandmothers. The others were aunts and other female relatives of the kids; it is maybe a better idea to expand the term “grandmother” to include any senior woman who helped raise the children of younger women (Jacobson, 2013).
A further theory suggest to help explain the grandmothers is the “absent father hypothesis”. This proposes that “reduced paternal investment linked with increasing maternal age was a supplementary impetus for the evolution of menopause” (Guiton 1989; Kuhle 2007; Schwartz 2008). The reduced paternal investment may have been connected with rising maternal age for two reasons: the first one is a men’s defection from their middle-aged wife’s and the second reason is that men’s as a rule dies earlier than females. It is important to be clear that the “absent father hypothesis” is not a substitute for the “grandmother hypothesis” but to a certain extent some kind of balance. It outlines an additional cost of reduced paternal investment which is associated with continued reproduction by ancestral women that could have been an additional impetus for the evolution of menopause ( Guiton 1989, Kuhle 2007, Sschwartz 2008).
In conclusion, there is no any doubt that grandmothers are helpful and very important in many modern or rural societies, but in the other hand, although this is a very interesting theory, yet does not prove in any case that the grandmothers have been the driving force for developing human longevity.
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