The theory
that mothers become infertile in middle age so that they can help care for
their grandchildren is under attack, raising new questions about female
identity
The Guardian, The Observer, Angela Saini, Sunday 30 March 2014
 |
Safe hands: the grandmother hypothesis, along with competing theories to
explain menopause, is hard to prove because there are almost no similar
species to compare us with. Photograph: Alamy |
Sitting at
my desk today is a benefit made possible by my mother-in-law. She is taking
care of my son, leaving me free to do other work and ideally, in biological
terms, have more babies. That, in short, is the leading explanation for why she
and other women of her age have evolved to stop having babies of their own and
live long post-menopausal lives. It's known as the grandmother hypothesis.
However,
this idea, and its comforting portrait of family cooperation, is being
challenged. It has been half a century since scientists began to explore why
human females were one of only a couple of species to became infertile so early
in their lives. The American evolutionary biologist George Williams wrote in
1957 that the menopause may have emerged to protect older women from the risks
linked to childbirth, keeping them alive long enough to make sure their
children grew up to have grandchildren.
Since then,
the scientific debate has heated up. As the study of menopause has grown, with
more female researchers joining the ranks, it has become tinged with gender
politics. Indeed, some scientists have even been the target of abusive mail
from the public. The reason behind the menopause is no longer just a biological
conundrum; it's a question of female identity.
On one side
of the divide are those who insist that older women have proven themselves so
useful they have evolved to survive beyond their reproductive years. On the
other are those who claim that the menopause is little more than a by-product
of increased longevity or, more controversially, that infertility arose simply
because men don't fancy older women.
Answers to
the problem may be coloured by gender bias, suggests Dr Rebecca Sear, an
evolutionary demographer at the London School of Hygiene and Tropical Medicine.
"A lot of menopause work is done by women," she says. In contrast,
"a lot of work on sexual selection by men is done by men".
At the
heart of the menopause puzzle are two biological facts: nature is efficient,
and the purpose of life is to reproduce. Chimps in the wild, for instance,
rarely survive beyond their 40s. Elephants live longer but carry on having
babies into their 60s. A long post-menopausal life is so rare a phenomenon in
nature that humans are believed to share it with only a couple of species of
whale.
Humans are
unusual in other ways, too. Our infants depend on us for far longer than those
of other species do; and we co-operate. All this implies that the contribution
of grandmothers may be vital.
In the
1980s the grandmother hypothesis got a boost thanks to the fieldwork of Professor Kristen Hawkes, an anthropologist at the University of Utah.
Observing the Hadza, a partly hunter-gatherer tribe in Tanzania who she says
live a life as close to our early ancestors as anyone is likely to find today,
she came to a surprising revelation. "There they were right in front of
us. These old ladies who were just dynamos," she says. There was a
division of labour in the tribe that not only included older women, but
depended on them.
According
to Sear, whose work has also shown that grandmothers improve child mortality in
some societies, this should hardly have been surprising. It is only our
assumptions, she says, which are built on decades of research that put men at
the heart of evolution, that make it appear odd.
"It is
estimated that women do 80% of the work in African subsistence agricultural
societies, even into old age," says Sear. "The man-the-hunter model
of human evolution really does drive me nuts. Men and women in hunter-gatherer
societies tend to bring back equal amounts of food. The idea that women are new
to the workplace is outdated."
Hawkes
found that the Hadza grandmothers helped their daughters raise more and
healthier children. They were vital to reproduction even if they weren't themselves
having babies. She claims mathematical models prove that this contribution –
small though it may seem – could be important enough to account for why women
who can no longer give birth have evolved to live for so long.
Last year,
however, evolutionary biologist Dr Rama Singh, at McMaster University in
Canada, came up with a completely different explanation. He and two colleagues
also at McMaster, Richard Morton and Jonathan Stone, published a controversial
paper that claimed that men were the reason for female infertility.
"Let's
assume mating is not random. We know that men, young and old, prefer younger
women. So in the presence of younger women, older women will not be mating as
much," says Singh. If they aren't having sex, his argument goes, they
don't need to be able to reproduce.
Hawkes and
Sear are among his critics. "It's a stupid argument and it was trashed
when it came out. It's a circular explanation. The reason men don't prefer
post-menopausal women is that they're post-menopausal and they can't get
pregnant, not the other way round," says Sear.
Singh,
meanwhile, insists that his argument is obviously correct. "Whether you
believe it or not, just look around society today. The science is cut and dry.
The problem with evolutionary biologists is that they like a story. The truth
is, nature doesn't care about sympathy or feeling," he says. His lab,
which focuses on male sexual selection, is now working to find out when in
history the menopause evolved.
But this
dogged focus on male sexual selection is out of date, suggests Hawkes. "So
much of the focus of human evolution was on what men were doing," she
says. The grandmother hypothesis has changed that.
That is not
to say that grandmothers are necessarily heartwarmingly selfless babysitters. A
supplement to the theory proposes that inter-generational conflict is what
forces women into caring for their grandchildren rather than having babies of
their own. Dr Virpi Lummaa, an evolutionary biologist at the University of
Sheffield, studied church parish record data in Finland, finding that if
resources are limited, infant survival was drastically reduced if
daughters-in-law and mothers-in-law had babies at the same time.
"If a
mother-in-law cares for her grandchildren, she still benefits because she is
genetically related to them. There is no such benefit the other way round for
the daughters-in-law," says Lummaa.
Less
harmonious though this family picture may be, it still affirms that the
menopause does not mark the beginning of the end as far as nature is concerned,
but the start of another equally productive phase in a woman's life.
The
menopause question is a particularly tough one for scientists because there are
almost no species to compare us with. The notable exception is the female
killer whale, which stops reproducing in her 30s or 40s but can survive into
her 90s.
In this
case, there seems to be less of a "grandmother effect", than a
"mother effect", according to Dr Darren Croft, a behavioural
ecologist at the University of Exeter, who is studying whale menopause.
"Our research shows that female killer whales act as lifelong carers for
their own offspring, particularly their adult sons," he says.
However,
with evolutionary research of this kind, which looks at behaviour and culture,
theories are so difficult to prove that almost anything can be true, says Sear.
"The problem with the evolution of a trait is you can never know for
certain. Basically, you can make a model tell you anything."
Among the
explanations out there, Sear, like many researchers in the field, does at least
find the grandmother hypothesis plausible. "I do also like hypotheses that
give women some agency in evolution," she says. "It is encouraging
that, hypothetically, there might be a use for me after menopause."
Related Articles:
Question: Dear Lee/Kryon: In my psychotherapy practice, I am specializing in menopause and other women's life transition issues. I am trying to frame menopause as a step within the spiritual evolutionary process, perhaps even part of the female response to ascension. Can you help me with an explanation of what the process of menses means for my clients? And how is it that females seem to undergo this "reverse puberty" process in a more dramatic way than men do?
Answer: Again we say to you that you must remove the biological from the spiritual. Look at what the body does. It is geared to stop the engine of procreation so that the female will not be harmed. That's why it occurs at all. It is an engine of appropriateness related to age. It's also an old paradigm, however, since we teach that you can extend your life-span, and that also means bearing children longer with safety, if that is part of your life plan.
For a male, the evolutionary process is one where, since he does not give birth, his biology is not one that goes through anything in the birth process. Therefore age is unimportant to his health when it comes to producing the seeds, which he can do almost until death.
So the body is protecting the females from undue stress, and even from premature death - going through childbirth when the chemistry is not up to it. This should be seen as a blessing, and one that is honored.
However, now we tell you something that is more along the lines of your question. In females, sometimes the process isn't stopped for biological reasons at all, but spiritual ones! In males, sometimes the hormones of desire and performance are also seemingly prematurely stopped. Ever wonder why this might happen?
The reason? Sometimes shamans need to have some of the common distractions of earth eliminated so that their concentration can be focused more clearly on spiritual matters. Don't read anything into this. It's different for every Human Being, so there is no generality here. But you should know that this is often part of the process of "relief from the distraction of things that are no longer needed," given for spiritual enlightenment. Not for all, but for many. This is often why you perceive elders to be wiser. They don't have that set of very complex and demanding chemicals surging through their body, either giving them pain with each cycle, or the pain of desire without fulfillment, which has its own attributes of psychological frustration and distraction.
For the females: Think of these things as all related. What is it you need? Do you give permission for it? Is it appropriate in your contract? Then when it comes, talk to your cellular structure and replace the chemistry that needs to be there for your energy, and say good-bye to that which is leaving. Give ceremony around it. You may do all of this naturally, talking to your cells. They will respond, and create what is missing.
This is the new Human Being, taking control of their bodies, and speaking directly to their cells. Creating tissue and chemistry naturally, since the cellular structure of your body is "listening" to what you need, and is far more capable than any scientist has ever told you.
And this is the truth.
