The Origin of Menopause: Why Do Women Outlive Fertility?

AGE-OLD QUESTION: Scientists explore why women live long after they lose their ability to reproduce whereas many other female organisms die once they can no longer reproduce.
Ronald Bloom/Stockphoto

The origin of menopause has puzzled evolutionary biologists for the last half-century. Three new studies attempt illumination. The real question, though, is probably not: Why menopause? Rather, it is: Why do women long outlive their fertility?

Human ovaries tend to shut down by age 50 or even younger, yet women commonly live on healthily for decades. This flies in the face of evolutionary theory that losing fertility should be the end of the line, because once breeding stops, evolution can no longer select for genes that promote survival.

The most popular explanation, the "grandmother hypothesis," argues that a generous post-reproductive life span makes sense if a grandmother improves the survival and reproduction of her grandchildren, thus ensuring continuation of her own genes—including genes that contribute to longevity. But skeptics say the math is askew. From an evolutionary perspective, it is hardly ever better for a woman to give up a chance to bear additional children of her own, and so pass on half her genes, for the sake of improving the survival of her grandchildren, who carry only a quarter of her genes.

"The problem is that these grandmother benefits aren't big enough to ever favor stopping breeding between the ages of 40 and 50," says Michael Cant, an evolutionary biologist at the University of Exeter in England and co-author of a new study on the genesis of menopause published this week in Proceedings of the National Academy of Sciences USA. "When you look at data from hunter-gatherers and other natural fertility populations, the sums just don't add up." Grandmothers do benefit their descendants, he says, but the genetic payoff is small compared with those of producing another child.

Cant and co-author Rufus Johnstone, an evolutionary biologist at the University of Cambridge in England, used game theory to argue that menopause is early cessation of reproduction that originated through reproductive conflict between generations. In most cooperatively breeding species, reproduction is suppressed in younger females, who act as helpers to older reproducing females. By contrast, they say, younger women in human social groups win the reproductive sweepstakes, because the older ones stop having babies.

"We showed that, compared to other primates that exhibit a post-reproductive life span, humans really stand out, because there is absolutely no overlap in reproduction between generations," Cant says. "Women stop breeding on average when the next generation starts to breed."

This makes evolutionary sense, Cant and Johnstone say, because, contrary to most mammals, young women tend to move to their mates' communities, where they become immigrants whose only genetic kin are their own children. There is no genetic profit in helping their mothers-in-law bear more children, because they will not share any genes with those children. But an older woman who helps her son's wife reproduce will benefit by bequeathing 25 percent of her genes to her grandchildren.

"We show that the mother-in-law's best strategy is to stop breeding, avoid competition, and allow the daughter-in-law to breed and help her," Cant says. "It's the first time anyone has taken the idea that humans evolved with this sex bias in dispersal and looked at the implications for how these conflicts will be resolved within the family."

The mother of the grandmother hypothesis, anthropologist Kirsten Hawkes of the University of Utah, says Cant and Johnstone are right to focus on intergenerational conflict. Elephants have babies in their 60s, and some whales give birth in their 80s. "It's clearly something selection can adjust," she says. "So explaining why it hasn't in us has to be part of the story." But she disputes their claim that female-bias dispersal is, in fact, the universal human/ape residence pattern, pointing out that half of the young female chimps at anthropologist Jane Goodall's Gombe Stream Research Center remain with their mothers, and that recent studies show that hunter-gatherers often live with the wife's family as well.

Another explanation for menopause is the "mother hypothesis," which holds that it occurs because older mothers might profit more, genetically speaking, by investing resources in their existing children than in giving birth to new ones. Researchers at the Max Planck Institute for Demographic Research in Rostock, Germany, make the case for this in the American Journal of Physical Anthropology (AJPA), concluding that menopause is advantageous when a woman has aged enough to face an increased risk of stillbirth, birth defects and her own death in childbirth.

Researchers of a different AJPA study, based on 400 years' worth of data on births in Costa Rica, believe that postmenopausal longevity is associated with an increased number of children but a decreased number of grandchildren—a finding that supports mothers over grandmothers.

"We're not saying grandmothers do not provide benefits in some societies," says study co-author Lorena Madrigal, an anthropologist at the University of South Florida in Tampa. But, "we should not assume that one pattern fits all."

Data on great ape fertility is spotty, but what there is shows that our closest relatives—chimps, bonobos, gorillas, even orangutans—stop having babies about the same age that we do: the late 30s. The difference is, they generally die a short time later. "The thing that makes us different from apes is not the age of fertility decline, it's the lack of aging in other systems," says Hawkes. "I have been saying this for a long time and I don't think it's what anybody is hearing. Probably what a lot of people are prepared to listen to is the way Cant and Johnstone have framed this, that the real question is: 'Why do we stop [reproducing] so early?' I think the bottom line is that, compared with our closest living relatives, we don't."

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Peak oil

If one accepts that climate change could be catastrophic for many ecosystems, including the multiple ones humans inhabit, what could possibly be considered more critical, more demanding of our full attention, right now?

The mother of all asteroids intersecting with our planet's orbit? All-out nuclear war? Aliens?

Well, try "peak oil" (put simply, the point at which the rate of global oil production begins to decline).

Richard Gilbert

Peak oil has "the imperative of urgency," according to Richard Gilbert, an urban-issues consultant based in Toronto.

"The likely outcome of not dealing with this issue is not an environmental catastrophe. It's an economic and social catastrophe that may leave us unable to deal with the environmental catastrophe," he said in an interview.

In Transport Revolutions: Moving People and Freight Without Oil, Gilbert and co-author Anthony Perl, an urban studies professor at Simon Fraser University, make a persuasive argument that global oil depletion is more imminent, and for that reason more important, than climate change.

Anthony Perl

One way or another, they say, there is a revolution coming.

"It is as if the power for our life-support system were about to be cut off by a blackout," the authors write in their book, the cover of which is adorned with a photo of a freighter attached to a SkySail, a large, wind-propelled towing kite that substitutes part of a ship's engine power.

The gushers are gone

CANADIAN PERSPECTIVE

For predictions from Anthony Perl and Richard Gilbert regarding how Canada would fare in an oil crisis, read excerpts from their interviews with Eve Savory.

In case you've missed the vigorous and contentious debate about peak oil, think of it as the time when half of all the oil that ever could be produced has been produced, whether that is from one particular field or from the planet's total supply.

More importantly, think of it as the end of easy oil.

"It's the end of the Beverly Hillbillies oil," Perl said. "The kind of oil that you stick a hole in the ground, and it starts squirting a gusher out under its own power."

In other words, the end of cheap oil.

At the same time as cheap oil declines, demand is increasing. Supply cannot keep up.

Predicting the date of peak oil is tricky. It involves many variables, such as the projected rates of consumption, how much oil is actually still in the ground and whether new technology could allow reserves that are currently unreachable to be tapped in the future.

YOUR INTERVIEW

What do you think about the peak oil issue? If you have questions for Richard Gilbert and Anthony Perl, pose them here. We'll forward the questions to the authors and publish their answers.

If peak oil is many decades away,as some believe, there will be time for alternative energy technologies to be developed and adopted. The economic argument is that a free market will solve peak oil as soon as the price is high enough, by encouraging people to develop other sources of energy.

Gilbert and Perl believe those arguments underestimate the danger.

"The geological literature is more compelling than the economic literature," Perl said.

But whether one concludes, as Perl and Gilbert have, that the peak in global oil production is likely to occur in 2012 or far in the future, oil is inarguably a finite resource. More importantly, oil post-gusher will be more expensive, dangerous and politically risky than previously.

If peak oil theorists are right, countries such as the U.S. and the U.K., which have managed to increase consumption by importing oil, may eventually find there won't be oil to import.

The $1,000 plastic Santa

So, what does this mean for you?

Well, 95 per cent of all motorized transportation is fueled by oil. Almost half of that is freight. And freight has shaped what our economies, and hence our societies, have become.

Canadian Perspective

To read Eve Savory's Q&A with the authors of Transport Revolutions: Moving People and Freight Without Oil regarding how they expect Canada would fare in an oil crisis, click here.

"The economies of the countries of the world in a sense float on a sea of oil," Gilbert said. "They need that transportation to function in the way that they do now."

Oil at $250 US a barrel would be "the equivalent of a Category 5 hurricane hitting the entire North American continent at the same time," said Perl. "There is no way for society to continue with these price increases without either an economic collapse or some kind of military crisis, or both."

How much would you be willing to pay for the plastic Santa from China? Orange juice in Calgary? And what about things our society considers essential — say, hospital beds and medicine, fire trucks and computers?

So, as we enter what Gilbert and Perl believe is the era of global oil depletion and oil prices rise (they have roughly quadrupled in the last four years), both men speak soberly of possible chaos.

"It's the kind of thing that could tip different economies, maybe the whole world, into an economic recession, which we know brings profound social disruption." Gilbert said.

Think the dirty thirties. And war.

"People will not just sit by and watch their societies and communities go extinct without some kind of response, beyond economic responses. That leads to a more turbulent world," said Perl.

Oil-rich Western Canada would be a choice morsel to court or conquer.

Revolution = sudden and dramatic change

Which brings us to the authors' transport revolution. Or revolutions, for they posit two.

In one, it is business as usual, and slowly the lights go out.

Gilbert and Perl see expensive oil turning life in the developed world cold, dark and bitter. They write that in a worst-case scenario, "car-dependent suburban residents … will have to abandon their homes or live at a subsistence level on what they can produce from their land."

As The Atlantic magazine recently wrote in a different context, suburban McMansions will become the country's slums.

That's the "bad" revolution. Or, say the authors, we can electrify our world.

Here is the authors' prescription for a successful transport revolution:

Start by moderating demand. Tax oil. Stop the planning and construction of all future infrastructure intended for oil-based transport, i.e. airports and freeways.

And start planning — by 2010 — for a rapid shift to electric propulsion. Electrify the existing railways and roadways and shift freight and personal travel to rail, trolley and bus, to electric scooters and personal grid-connected vehicles (known as GCVs).

Ships would move by sail, reserving oil-powered engines for tricky maneuverings in port and in storm. Aviation would be confined to very large, fuel-efficient planes.

"Electricity is the perfect energy carrier for an uncertain future because it's a carrier; it's not a source of energy," Perl said.

Hydro, tidal, geothermal, wind, ethanol and, yes, coal and nuclear all can feed into the grid during the transition, Perl and Gilbert write.

By 2025, the authors believe, 30 per cent of transportation in the U.S. can, and must, complete the shift away from oil. The cost, not surprisingly: trillions of dollars. On the other hand, they say, some of that money would be redeployed from airport and highway construction and maintenance. Against the rising cost of oil and the risk of societal collapse, those trillions are a bargain, they say.

"There will still be, hopefully, a global economy and trade and such. The difference is it will have to move differently than it does now," Perl said.

And more slowly.

WW II's recipe for change

Wildly impossible? Sci-fi fantasies dreamed in an ivory tower? Perhaps not, for the authors looked back as well as forward when devising their proposals, examining five previous revolutions in transport. One in particular is remarkable.

They call it the Great Pause. In 1941, before Pearl Harbour yanked the U.S. into the Second World War, American auto companies manufactured 3.8 million cars. Priorities changed on Dec. 7.

RELATED LINKS:

Among the multitude of websites dealing with future energy production and consumption is the U.S. National Petroleum Institute's 380-page document Hard Truths.

A widely quoted source is the Association for the Study of Peak Oil and Gas. The Canadian branch of the international organization is here.

And if all this has made you need a laugh, check out these topical cartoons.

Within weeks, the War Production Board ordered a halt to the production of cars and light trucks. Steel, assembly lines and labour were turned to the making of bombers and anti-aircraft guns. Gasoline and tires were rationed.

By 1943, just 143 vehicles were produced. A "golden age" for public transit lasted through the war years.

"Individual sacrifice was justified in the name of national security, a recipe for legitimizing sudden and dramatic behavioural change," write Gilbert and Perl.

That is their recipe for action today.

"We need systemic change, and systemic change can only be initiated by governments," Gilbert said. "If people wait until the world really is in crisis, the risks … are much higher," said Perl.

Yet governments that claim to be greatly concerned about climate change have done little to attempt to change our behaviour. Whether peak oil is imminent or half a century away, what likelihood is there that governments will take action before a crisis hits?

Perhaps we will have to first experience the "bad" revolution, the one where our world gets small and cold and dark, before we are convinced to tackle the one that slows us down — but keeps us moving.

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I’ve found God, says man who cracked the genome

THE scientist who led the team that cracked the human genome is to publish a book explaining why he now believes in the existence of God and is convinced that miracles are real.

Francis Collins, the director of the US National Human Genome Research Institute, claims there is a rational basis for a creator and that scientific discoveries bring man “closer to God”.

His book, The Language of God, to be published in September, will reopen the age-old debate about the relationship between science and faith. “One of the great tragedies of our time is this impression that has been created that science and religion have to be at war,” said Collins, 56.

“I don’t see that as necessary at all and I think it is deeply disappointing that the shrill voices that occupy the extremes of this spectrum have dominated the stage for the past 20 years.”

For Collins, unravelling the human genome did not create a conflict in his mind. Instead, it allowed him to “glimpse at the workings of God”.

“When you make a breakthrough it is a moment of scientific exhilaration because you have been on this search and seem to have found it,” he said. “But it is also a moment where I at least feel closeness to the creator in the sense of having now perceived something that no human knew before but God knew all along.

“When you have for the first time in front of you this 3.1 billion-letter instruction book that conveys all kinds of information and all kinds of mystery about humankind, you can’t survey that going through page after page without a sense of awe. I can’t help but look at those pages and have a vague sense that this is giving me a glimpse of God’s mind.”

Collins joins a line of scientists whose research deepened their belief in God. Isaac Newton, whose discovery of the laws of gravity reshaped our understanding of the universe, said: “This most beautiful system could only proceed from the dominion of an intelligent and powerful being.”

Although Einstein revolutionised our thinking about time, gravity and the conversion of matter to energy, he believed the universe had a creator. “I want to know His thoughts; the rest are details,” he said. However Galileo was famously questioned by the inquisition and put on trial in 1633 for the “heresy” of claiming that the earth moved around the sun.

Among Collins’s most controversial beliefs is that of “theistic evolution”, which claims natural selection is the tool that God chose to create man. In his version of the theory, he argues that man will not evolve further.

“I see God’s hand at work through the mechanism of evolution. If God chose to create human beings in his image and decided that the mechanism of evolution was an elegant way to accomplish that goal, who are we to say that is not the way,” he says.

“Scientifically, the forces of evolution by natural selection have been profoundly affected for humankind by the changes in culture and environment and the expansion of the human species to 6 billion members. So what you see is pretty much what you get.”

Collins was an atheist until the age of 27, when as a young doctor he was impressed by the strength that faith gave to some of his most critical patients.

“They had terrible diseases from which they were probably not going to escape, and yet instead of railing at God they seemed to lean on their faith as a source of great comfort and reassurance,” he said. “That was interesting, puzzling and unsettling.”

He decided to visit a Methodist minister and was given a copy of C S Lewis’s Mere Christianity, which argues that God is a rational possibility. The book transformed his life. “It was an argument I was not prepared to hear,” he said. “I was very happy with the idea that God didn’t exist, and had no interest in me. And yet at the same time, I could not turn away.”

His epiphany came when he went hiking through the Cascade Mountains in Washington state. He said: “It was a beautiful afternoon and suddenly the remarkable beauty of creation around me was so overwhelming, I felt, ‘I cannot resist this another moment’.”

Collins believes that science cannot be used to refute the existence of God because it is confined to the “natural” world. In this light he believes miracles are a real possibility. “If one is willing to accept the existence of God or some supernatural force outside nature then it is not a logical problem to admit that, occasionally, a supernatural force might stage an invasion,” he says.

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Top 5 Recreational Drug Experiments

Recreational drugs are a ridiculously fun topic for scientific research. They could also be the inspiration for powerful new medications. We are often amazed by the fascinating, and sometimes hilarious, stories that make their way into peer-reviewed journals. Here are some of our very favorites:

5. Harvard Scientists Build a Device to Smoke Weed During a Brain Scan
To better understand addiction, and how to treat it, scientists need to get a better look at the human brain as it is under the influence of weed. Unfortunately, smoking weed inside the narrow chamber of a functional MRI is not easy. To prevent smoke damage and allow their research subjects to puff without moving around too much, Blaise Frederick and his team at Harvard built what amounts to a giant bong.

4. Stanford Chemists make THC from Scratch
Since 1965, chemists have been trying to make the active ingredient of marijuana [pdf]from scratch. Back then, the researchers could only make tetrahydrocannabinol along with its enantiomers -- impurities that have the same chemical composition, but a different shape. Then, in 2006, a pair of chemists from Stanford University used a Molybdenum catalyst and other sophisticated techniques to produce the coveted molecule in its pure form. Despite their discovery, mother nature is still the best chemist and closets with high-intensity lamps will outperform the most sophisticated laboratories.

3. Researchers Learn How Salvia Works
Diviner's sage contains a powerful hallucinogen that may someday inspire a new class of depression, pain, and addiction medications. In at least one instance, a woman has used the substance to rid herself of depression. Tests on animals have shown that the Oxaccan plant, a relative of the culinary herb, can also control pain.

Last year, Catherine Willmore and her colleagues at Ohio Northern University ended a controversy about how the drug works. In the Sep. 2007 issue of Neruopharmacology, she confirmed that the active chemical, Salvinorin A, binds to signal-carrying proteins called kappa opioid receptors.

Willmore and her team trained rats to recognize the sensations caused by a well-understood drug that also targets kappa opioid receptors. It is impossible to know exactly how the rats felt during the test, but they could not tell the difference between the active chemical in sage and the one they had been trained to identify. Since the drugs feel the same, both of them must activate the same target.

2. British Army Tests LSD on Soldiers

1. Researchers Combine Chemicals from Sea Urchin Eggs and Weed to Make Powerful Painkillers
Scientists at organix, a small research and development firm, made hybrid molecules which resemble the euphoria-causing compounds THC and anandamide. In the Dec. 2007 issue of Bioorganic and Medicinal Chemistry they explained that both drugs have their own unique advantages and disadvantages. Anandamide starts working faster than its marijuana-derived counterpart, but it is more quickly destroyed by the body. A fusion of the two chemicals may last longer while maintaining an equal or stronger effect.

Although the researchers at Organix did not comment on the recreational potential of their new chemicals, their data makes it very clear that the new drugs push the same pleasure buttons as THC and anandamide.

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Gravity Waves Make Tornados

March 19, 2008: Did you know that there's a new breakfast food that helps meteorologists predict severe storms? Down South they call it "GrITs."

GrITs stands for Gravity wave Interactions with Tornadoes. "It's a computer model I developed to study how atmospheric gravity waves interact with severe storms," says research meteorologist Tim Coleman of the National Space Science and Technology Center in Huntsville, Alabama.

According to Coleman, wave-storm interactions are very important. If a gravity wave hits a rotating thunderstorm, it can sometimes spin that storm up into a tornado.

Above: Click on the image to watch a gravity wave roll over Tama, Iowa, on May 7, 2006. Credit: Iowa Environmental Mesonet Webcam.

What is an atmospheric gravity wave? Coleman explains: "They are similar to waves on the surface of the ocean, but they roll through the air instead of the water. Gravity is what keeps them going. If you push water up and then it plops back down, it creates waves. It's the same with air."

Coleman left his job as a TV weather anchor in Birmingham to work on his Ph.D. in Atmospheric Science at the University of Alabama in Huntsville. "I'm having fun," he says, but his smile and enthusiasm already gave that away.

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"You can see gravity waves everywhere," he continues. "When I drove in to work this morning, I saw some waves in the clouds. I even think about wave dynamics on the water when I go fishing now."

Gravity waves get started when an impulse disturbs the atmosphere. An impulse could be, for instance, a wind shear, a thunderstorm updraft, or a sudden change in the jet stream. Gravity waves go billowing out from these disturbances like ripples around a rock thrown in a pond.

When a gravity wave bears down on a rotating thunderstorm, it compresses the storm. This, in turn, causes the storm to spin faster. To understand why, Coleman describes an ice skater spinning with her arms held straight out. "Her spin increases when she pulls her arms inward." Ditto for spinning storms: When they are compressed by gravity waves, they spin faster to conserve angular momentum.

"There is also wind shear in a gravity wave, and the storm can take that wind shear and tilt it and make even more spin. All of these factors may increase storm rotation, making it more powerful and more likely to produce a tornado."

"We've also seen at least one case of a tornado already on the ground (in Birmingham, Alabama, on April 8, 1998) which may have become more intense as it interacted with a gravity wave."

Above: Click on the graphic to play an actual Doppler radar movie of a gravity wave interacting with a rotating thunderstorm and making it stronger in northwest Alabama on Jan. 22, 1999. Credit: NOAA.

Coleman also points out that gravity waves sometimes come in sets, and with each passing wave, sometimes the tornado or rotating storm will grow stronger.

Tim and his boss, Dr. Kevin Knupp, are beginning the process of training National Weather Service and TV meteorologists to look for gravity waves in real-time, and to use the theories behind the GrITs model to modify forecasts accordingly.

Who would have thought grits could predict bad weather? "Just us meteorologists in Alabama," laughs Coleman. Seriously, though, Gravity wave Interactions with Tornadoes could be the next big thing in severe storm forecasting.

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