Re: Fwd: Theorists See Evolutionary Advantages In Menopause

From: Philip A.E. Jonkers (
Date: Thu Nov 29 2001 - 00:24:52 GMT

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    Subject: Re: Fwd: Theorists See Evolutionary Advantages In Menopause
    Date: Wed, 28 Nov 2001 16:24:52 -0800
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    On Tuesday 27 November 2001 05:44 pm, you wrote:
    > September 6, 1997
    > Theorists See Evolutionary Advantages In Menopause
    > THE Hadza people of northern Tanzania are a small group of
    > hunter-gatherers who share a language, a culture and a distaste for
    > gardening. Time and again, government and church agencies have sought to
    > transmute them into full-time farmers, but the Hazda have always returned
    > to the bush, where they subsist on wild goods like fruits, honey, tubers
    > and game. The terrain is hard and hilly, and so is the life, but on one
    > incomparable resource the foragers can always rely: a pack of old ladies
    > with hearts like young horses.
    > As Dr. Kristen Hawkes of the University of Utah and her colleagues have
    > found in their extensive studies of the Hadza, women in their 50's, 60's,
    > 70's and beyond are among the most industrious members of the group. They
    > are out in the woods for seven or eight hours a day, gathering more food
    > than virtually any of their comrades.
    > When a young woman is burdened with a suckling infant and cannot fend for
    > her family, she turns for support, not to her mate, but to a senior
    > female relative -- her mother, an aunt, an elder cousin. It is Grandma,
    > or Grandma-proxy, who keeps the woman's other children in baobab and
    > berries, Grandma who keeps them alive. She is not a sentiment, she is a
    > requirement. As Dr. Hawkes, Dr. James O'Connell of the University of Utah
    > and Dr. Nicholas Blurton Jones of the University of California at Los
    > Angeles report in the latest issue of Current Anthropology, a nursing
    > Hadza woman always has a postmenopausal helper.
    > There are only about 750 Hadza, and they are contemporary
    > hunter-gatherers, not pristine relics of prelapsarian humanity.
    > Nevertheless, the centrality of elder women to their group's survival has
    > thrown fresh kindling on the spirited debate over the origins and purpose
    > of human menopause.
    > As doctors and women thrash out the best way to ''treat'' menopause,
    > pitting the benefits of estrogen therapy to the heart and bones against
    > the risks the hormone poses to the breast and possibly the ovaries,
    > evolutionary scientists address the menopause mystery from a more
    > high-flown, though no less quarrel-prone, perspective. They ask whether
    > menopause is an ancient adaptation or a contemporary artifact. Is it the
    > well-wrought product of natural selection, or the incidental byproduct of
    > an unnaturally prolonged life span?
    > Proponents of the adaptationist camp generally see menopause as the
    > thriftiest solution to the problem of exorbitant offspring. By this view,
    > the ludicrous amount of time required for a mother to rear children to
    > maturity led to the need for so-called premature reproductive senescence,
    > an early retirement program for the ovaries. Through the mechanism of
    > menopause, an ancestral woman theoretically was spared the risks of
    > childbirth, and thus had a heightened chance of living long enough to see
    > her existing children out the door. Dr. Jared Diamond, a physiologist at
    > the University of California at Los Angeles Medical School has said that
    > menopause, like big brains and upright posture, is ''among the biological
    > traits essential for making us human.''
    > The artifactualists insist that prehistoric women almost never survived
    > past the age of 30, let alone long enough to experience the thrill of hot
    > flashes. By their reckoning, menopause is a modern luxury, the result of
    > women now outlasting an egg supply that more than sufficed for the cameo
    > appearances that their Stone Age foremothers called lives. ''For most of
    > our existence, we simply didn't live very long,'' said Dr. Alison
    > Galloway, an anthropologist at the University of California at Santa
    > Cruz. ''Menopause happens because, through technology, we've extended our
    > lives to the point where we run out of egg follicles. There's nothing
    > beneficial about it.''
    > Dr. Hawkes lends a new spin to the debate, combining elements of each
    > camp and adding a few bold spirals of her own. She agrees with the
    > artifactualists that menopause per se is not an adaptation -- it is not
    > the product of selective design. A woman's ovaries do not shut down
    > ''prematurely,'' she says. They last 40 or 45 years, the same time as the
    > ovaries of our close relatives, chimpanzees and gorillas. In a sense, she
    > says, women do outlive their egg supply, which is fixed before birth and
    > cannot be added to, as men continuously generate new sperm.
    > On the other hand, Dr. Hawkes concurs with the adaptationists that
    > prehistoric women very likely often survived past menopause, and that
    > they were instrumental to the survival of their families. She goes
    > further. Only with the ascent of the grandmother, she says, were human
    > ancestors freed to exploit new habitats, to go where no other hominid or
    > primate had gone before, and to become the species we know so well.
    > ''The Grandmother Hypothesis gives us a whole new way of understanding
    > why modern humans suddenly were able to go everywhere and do
    > everything,'' Dr. Hawkes said. ''It may explain why we took over the
    > planet.''
    > In another new study that touches on the evolutionary basis of menopause
    > and maternal longevity, Dr. Thomas Perls of Harvard Medical School and
    > his colleagues describe in the current issue of Nature their finding that
    > women who lived to be at least 100 years of age were much likelier to
    > have remained fruitful well into middle age than a comparable group of
    > women who died at the age of 73. Looking at two sets of women born in
    > 1896 who were equivalent in race, religion and other factors but who
    > differed in their life spans, the researchers found that among the 54
    > women who died in 1969 at the age of 73, only 5.5 percent had given birth
    > in their 40's. By comparison, 19.5 percent of the centenarians had
    > children after 40, one of them at age 53.
    > Because the women in Dr. Perls's analysis all had their families before
    > the rise of fertility-enhancing technology, the researchers see the stark
    > discrepancy in maternal stamina between the two groups as evidence of
    > innate selective drives at work. They propose that the genes allowing the
    > centenarians to stay fruitful for an exceptionally long time continued
    > working long after menopause to lengthen the women's life spans,
    > supporting the view that a woman's extended survival is indeed crucial to
    > her offsprings' prospects.
    > The older a woman is at last birth, the more years she must stick around
    > to keep her family afloat. (The researchers also believe that menopause,
    > the complete cessation of fertility, evolved to prevent aging women from
    > dying in childbirth while they still had dependent young, but their
    > analysis of the centenarians offers no direct proof of that.)
    > The notion that menopause has adaptive value for women and their
    > offspring is itself getting a bit long in tooth. Dr. George C. Williams,
    > a renowned evolutionary biologist, first proposed it in 1957 to explain
    > the seemingly anomalous nature of human menopause. Other female primates,
    > and even species like fin whales and elephants that live into their 80's,
    > can continue bearing young to the bitter end, he pointed out.
    > Why are humans different? And why does menopause occur universally among
    > women, and during a short window of time -- at the half-century mark,
    > give or take four years -- while other depradations of age, like gray
    > hair or presbyopia, occur gradually and randomly? Dr. Williams saw in
    > menopause the thumbprint of natural selection, and suggested that the
    > early cessation of reproduction paradoxically enhanced a woman's
    > reproductive ''fitness,'' by assuring that she lived long enough to see
    > her children bear children themselves -- that she became a grandmother.
    > Others have picked up and expanded on the rudimentary Grandmother
    > Hypothesis. Dr. Diamond has proposed that aging women, and men, were
    > repositories of essential information in preliterate times, living
    > libraries for their clans, able to distinguish edible from poisonous
    > plants and to recall events of long ago that remained pertinent to
    > survival.
    > In traditional societies, clan members are often related, and so by
    > aiding the tribe the elders help themselves. Only women need protection
    > from the hazards of advanced maternity, Dr. Diamond says, and so only
    > women need to undergo premature reproductive senescence to keep them
    > around for the benefit of their kin.
    > Yet efforts to demonstrate the adaptive value of menopause have proved
    > elusive. Dr. Kim Hill and Dr. Magdalena Hurtado, anthropologists at the
    > University of New Mexico, spent years studying the Ache, a group of
    > hunter-gatherers living in eastern Paraguay. They tried to estimate the
    > impact of postmenopausal women on the welfare of their children and
    > grandchildren, to see if the presence of a grandmother had a measurable
    > effect, for example by reducing the mortality of grandchildren.
    > The anthropologists concluded that the Ache grandmothers did not make
    > enough of a cumulative difference to their families to justify, in
    > Darwinian terms, the loss through menopause of their own reproductive
    > capacity.
    > Using mathematical models, Dr. Alan Rogers of the University of Utah
    > estimated that a postmenopausal woman would have to double the number of
    > children her children bore, and eliminate infant mortality among those
    > grandchildren, to make menopause look like a sound strategy for
    > propagating one's genes. That is not a grandmother -- that is Neutron
    > Nana.
    > ''Adaptive menopause is an interesting idea, and I'm trying to keep an
    > open mind,'' said Dr. Steven N. Austad, a professor of zoology at the
    > University of Idaho in Moscow and author of ''Why We Age'' (John Wiley &
    > Sons, 1997). ''But I just don't see evidence to support it.''
    > Before anybody consigns the Grandmother Hypothesis to a conceptual
    > nursing home, however, Dr. Hawkes and her colleagues offer evidence in
    > the Hadza study that elder women can make an enormous, and quantifiable,
    > difference to their kin. The researchers found that whenever the mother
    > of young children gave birth to a new baby and was absorbed by the rigors
    > of breast-feeding, it was only through the intervention of a senior
    > female relative that the older children's weight stayed up. And the
    > harder the elders foraged, the higher the numbers on the researchers'
    > bathroom scale.
    > Importantly, the elder Hadza women were flexible in how they apportioned
    > their assistance. If a woman could help her nursing daughter, she did. If
    > she had no daughter, she helped a niece, or a cousin once removed.
    > Dr. Hawkes pointed out that in the Ache study showing little benefit from
    > grandma, the researchers had focused on the relationships between
    > mothers, their children and their children's children. Dr. Hawkes and her
    > colleagues were more inclusive in their analysis. ''If we restricted
    > ourselves to counting the reproductive success only of women whose moms
    > were still alive, we'd underestimate the effect of help from senior women
    > by a huge amount,'' Dr. Hawkes said. ''And you expect, with strategic
    > critters like ourselves, that natural selection would favor adjusting
    > help to where it was needed most.''
    > Dr. Hawkes proposes that what distinguishes a human female from her
    > chimpanzee or gorilla cousins is not that the woman goes through
    > menopause and the chimpanzee does not, but rather that the chimpanzee, at
    > 45 and with ovaries failing, is globally decrepit and close to death,
    > while a woman can live decades after follicular fadeout.
    > But young chimpanzees do not need elder females to help them. Once they
    > are weaned, they feed themselves, and so there are no selective pressures
    > to keep Aunt Chimsky alive. Only human children are fed for years after
    > leaving the breast, and a senior female can serve up nuts and berries as
    > well as can a mother, and better when mother is lactating.
    > Dr. Hawkes and her co-workers suggest that the extension of life past
    > menopause was a watershed event in human prehistory. With a labor force
    > of elder females available to help provision the young, adults were then
    > free to colonize new territories unavailable to those primates that did
    > not provision their weaned young, and that were thus restricted to
    > feeding grounds where the pickings were easy enough for juvenile fingers.
    > Suddenly humans could migrate to places where it required full adult
    > strength and cunning to extract food. They could go wherever they
    > pleased. After all, there were older women around to help.
    > Supporting this proposition are the foraging patterns of the Hadza. Very
    > young children find much of their food themselves, but they depend on
    > adults for half their calories, and those calories come from foods, like
    > deeply buried tubers, that only an adult can obtain. Growing old, then,
    > may be nothing new, and the postmenopausal years worthy of celebration
    > and gratitude. Grandma is great, she is strong, and she baby-sits for
    > free.
    > Copyright 2001 The New York Times Company
    > ===============================================================
    > This was distributed via the memetics list associated with the
    > Journal of Memetics - Evolutionary Models of Information Transmission
    > For information about the journal and the list (e.g. unsubscribing)
    > see:

    The reason for Grandma's post-menopause survival being her function in
    helping to raise big-brained meme-machines. Nice story indeed Wade.


    This was distributed via the memetics list associated with the
    Journal of Memetics - Evolutionary Models of Information Transmission
    For information about the journal and the list (e.g. unsubscribing)

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