Received: by alpheratz.cpm.aca.mmu.ac.uk id BAA20023 (8.6.9/5.3[ref pg@gmsl.co.uk] for cpm.aca.mmu.ac.uk from fmb-majordomo@mmu.ac.uk); Thu, 29 Nov 2001 01:25:22 GMT Content-Type: text/plain; charset="iso-8859-1" From: "Philip A.E. Jonkers" <phae@uclink.berkeley.edu> Organization: UC Berkeley To: memetics@mmu.ac.uk Subject: Re: Fwd: Theorists See Evolutionary Advantages In Menopause Date: Wed, 28 Nov 2001 16:24:52 -0800 X-Mailer: KMail [version 1.2] References: <20011128014427.AAA13267@camailp.harvard.edu@[205.240.180.83]> In-Reply-To: <20011128014427.AAA13267@camailp.harvard.edu@[205.240.180.83]> Message-Id: <01112816245200.01083@storm.berkeley.edu> Content-Transfer-Encoding: 8bit Sender: fmb-majordomo@mmu.ac.uk Precedence: bulk Reply-To: memetics@mmu.ac.uk
On Tuesday 27 November 2001 05:44 pm, you wrote:
> September 6, 1997
>
> Theorists See Evolutionary Advantages In Menopause
>
> By NATALIE ANGIER
>
> http://www.nytimes.com/1997/09/06/health/womenshealth/16MENO.html
>
> 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: http://www.cpm.mmu.ac.uk/jom-emit
The reason for Grandma's post-menopause survival being her function in
helping to raise big-brained meme-machines. Nice story indeed Wade.
Philip.
===============================================================
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: http://www.cpm.mmu.ac.uk/jom-emit
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