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Hey, good lookin' BEAUTY can win out over age.

When choosing sexual partners, men are more discerning than they're given credit for, going for attractive older women over younger women who would probably bear them more children.

"You'd think that men would always go for 20-yearolds, but they don't,' says evolutionary psychologist George Fieldman of Buckinghamshire Chiftems University College. 'Men prefer attractiveness over youthfulness when selecting a long-term partner."

In most animal species, including humans, males are generally thought to compete fbr as many partners as they can. Going for quantity over quality increases their chances of having the maximum number of offspring. But females are limited in the number cyf children they can have, so they choose the best-quality mate possible.

Now Fieldman has shown that men choose too. The researchers took a photo of a 36-year-old woman who was very attractive in the eyes of a group of men. They showed the photo to three other groups in their early 20s, along with photos of eight women aged 20 to 45 who'd been rated as less attractive. The researchers told each group that the beautiful woman was either 36, 41 or 45 years old. When asked who they'd prefer as a long-term partner, all three groups of men chose her, regardless of how old they thought she was.

The finding shows that men are not purely concerned about the number of offspring they might have, Fieldman says. They select beautiful women because they think their children will do better than the children of a younger but plainer woman. Joanna Marchant

Carbon sunk Is dumping greenhouse gases in the oceans pracicable? NS 30 June 2001

IT SEEMS like a great idea: slow global warming by pumping carbon dioxide to the bottom of the ocean, where it will remain locked up for centuries. But a new model of the process and an experiment to test the idea are stirring up debate about using our oceans as a dumping ground for greenhouse gases.

Heige Drange and his colleagues from the Nansen Environmental and Remote Sensing Centre in Bergen, Norway, used computer models to show that CO, dumped at a depth of 800 metres in the Norwegian Sea would dissolve before it bubbles to the surface. The heavier, gas-rich water would then sink to the bottom, flow into the Atlantic Ocean and not rise to the surface for centuries.

The idea is to extract CO, from waste gases, compress it to liquefy it, and spray it into the deep water as small droplets that can easily dissolve. "It's fairly simple," says Drange. The estimated cost of disposing of C02 in this way would be about $39 per tonne, compared with a tax of $32 per tonne

currently paid by offshore rigs in Norwegian waters for releasing C02 into the air. While the researchers acknowledge that further studies are needed, they think the plan could help to put a brake on global warming. But environmentalists argue that polluting the ocean to save the air will only create new problems and that the long-term effects are unknown. Some worry that the acidity of the C02-rich water will kill wildlife or dissolve parts of the seabed, and that climate change may alter ocean circulation, bringing the C02 back to the surface sooner than we now expect. An international team hopes to answer some of these questions by pumping a small amount Of C02 onto the seabed off Kona, Hawaii. But the project faces serious opposition from the public and has been scaled down several times already (New Scientist, 3 March, p 7). Stephen Masutani of the University of Hawaii in Honolulu expects it will be delayed until next year. "People are scared because it's an unknown," he says.

The Hawaiian project currently proposes to dump less than 40 tonnes Of C02 into the water over 10 days. On that scale, few people think the experiment will cause significant damage. But Paul Johnston of the University of Exeter, who works for Greenpeace, says that pursuing such projects may give people an excuse not to reduce their emissions. "It's a totally irresponsible way to convince people that there's a get-out-of-jail-free card. There isn't." Johnston doubts that any amount of research will ever prove the strategy safe. And, he estimates, the energy used to get the CO, liquefied and down to the sea floor could create about 40 per cent as much gas again. "You're going to make the problem worse in the long term,' he says.

Drange admits the strategy faces problems. But, he says, "We know the consequences of global warming. One should at least try to assess the possibilities." Nicola Jones More at: Geophysical Research Letters (vot 28, p 26371

IT'S A BURNOUT

Of the millions of eggs a woman is bom with, a mere few hundred stand the slimmest chance of making a baby. The rest languish in the ovaries getting steadily stale, or com.it suicide-mostly before a woman reaches the grand old ge of forty. It makes for some grim choices: either find a partner and establish your career in double-quick time that you can have your babies young, or risk leaving children until your eggs are no longer up to the job.

That, however, is all about to change. Fertility researchers are powering ahead with their bid to rewind the hands of the dreaded biological clock. That means girls being born today can probably safely leave child rearing until their 40s, 50s or even 60s. But while the coming revolution promises to be more liberating than the contraceptive pill, paternity leave and emancipation combined, it might just come with a nasty sting in its tail.

'The only thing in life that is so cataclysmic is this breeding business. You have to cram it in by your late 30s," says Alan Trounson, director of the Monash Institute for Reproduction and Development in Melbourne. 'We'll find a way to stop menopause being such a dramatic thing for women, but we have to make sure we do it safely."

Make no mistake, doctors face immense challenges in trying to understand the human egg-the key to delaying menopause. The human egg is.impossible to grow for any length of time in a lab dish, and while tucked away inside a woman's body, in its earliest stages it is invisible even with the help of the most sophisticated imaging equipment. Reproductive physiologists like to claim-with some justification-that we know more about outer space than we do about the inner workings of the human egg.

Even before a woman realises that she is pregnant, the cells that will form her grandchildren have been carefully set aside in her embryo, still less than the size of a rice grain. If the fetus is female, by the seventh month of pregnancy, those cells will have spawned a mind-boggling 7 million immature eggs.

From there on, though, it's all downhill. By the time a girl is born, numbers have plummeted to about 2 million-a mass slaughter whose purpose remains a mystery. Even then the carnage is far from complete. Over the next five decades, the egg population steadily diminishes as cells commit suicide in a series of defined stepsa process called apoptosis.

Of course, a few eggs escape that fate. When the girl hits puberty hormonal signals from the pituitary gland ensure that every few weeks groups of eggs start to mature. Nourished by a layer of granulosa cells, the chosen few take around six months to balloon up to 60 times their original size. Eventually, one egg outstrips the others, and ovulation occurs following another hormonal surge from the pituitary gland. The egg escapes from the ovary, and jets off into the fast lane of the Fallopian tube, and the possibility of a brief encounter with a sperm.

That onerous selection process means that by the time a woman has reached her late thirties, she's scraping the bottom of the ovarian barrel. By 45, her chances of getting pregnant the old-fashioned way "are very, very small," says Robert Winston, a leading fertility expert at Imperial College, London. "Even by IVF, it is only about 3 or 4 per cent."

According to current thinking those odds could be much improved if reproductive physiologists could find some way to stop the untimely deaths of immature eggs.

"My gut feeling is that menopause is determined by how many of the resting follicles you have feeding the pipeline to make more maturing follicles," says Jonathan Tilly, a reproductive biologist at the Vincent Center for Reproductive Biology at Harvard. Once that stockpile dries up, the pipeline shuts down, and the woman's reproductive system throws in the sanitary towel.

One way to stop that happening is to put your eggs on ice until you are ready to use them. Although human eggs are notoriously sensitive to freezing and thawing, these techniques are slowly edging into the mainstream-nowadays, clinics on at least three continents offer egg freezing to young women, and up to 60 babies worldwide have been born from frozen eggs.

Still, for now at least, the success rate remains low and none of the clinics New Scientist contacted is prepared to guarantee that its frozen eggs will be up to the job when they are defrosted. But if the tech, niques continue to improve, it's likely that babies born today won't bat an eyelid about freezing their eggs while they build a career or search for Mr Right. "It's an insurance policy," says Mohammed Taranissi, medical director of the Assisted Reproduction and

Gyiiaecological Centre in London.

But it's a costly and inconvenient one. The eggs can only be removed under sedation, after a series of unpleasant hormone injections. Far inofe convenient to find a way to keep immature eggs alive inside a woman's body-which is exactly what Tilly and his team are working towards. First they examined niece genetically engineered so they couldn't make a protein called Bax, which plays a key role in cell suicide. They found that young adult Bax-less females had three times as many eggs as normal, but could still produce pups-proof that blocking cell suicide improves egg survival and doesn't affect mouse fertility.

Two-year-old females-who'd be entitled to a telegram from the Queen if they were human-had a little more trouble making pups, but only because their bodies were too clapped out to carry a pfegnancy. Eggs from the old Bax-less mice still formed normal eiiibfyos when fertilised in a test tube.

Artificial wombs are unlikely ever to be an option (see "A bun in the husband, p 42), so that raises the question of how far into her dotage a woman could safely carry a pregnancy. No one knows for sure, but with the help of reproductive technology several women have given birth in their 60s. Many obstetricians suspect that the ability to carry a baby safely has more to do with a woman's overall fitness and health than her chronological age.

Good egg

Of course, tinkering with a women's genes to ward off the menopause is pie in the sky, but Tilly's team is also working on a drug that will block cell suicide. Young women undergoing treatment for cancers like leukaemia atid lymphoma urgently need this kind of research. Cheinotherapy and radiation mean that over 80 per cent of them go through an early menopause, sometimes while still in their twenties.

One way cancer therapy seems to work is by triggering the cascade of signals that instruct a cell to commit suicide-the immature egg cells simply get caught in the crossfire. Reasoning that there's absolutely no point in keeping damaged eggs hanging on by a thread-especially if they are to form the next generation, Tilly's team has found a way of blocking the very earliest stages of egg suicide. "We want to have a population of good oocytes, not the Night of the Living Dead oocytes," he says.

'To do this, they tried a drug called sphingosineI -phosphate (S I P), which has already been shown to halt cell suicide in human white blood cells. When Tilly's team injected the drug directly into the ovaries of mice and treated them with radiotherapy, the mice's immature eggs survived intact. They even went oh to form normal embryos in the test tube, and the pregnancy rate of irradiated mice treated with SlP was double that of the mice that didn't get the drug. "It's taken us 10 years to get to this point in mice, so it's going to take a while," says Tilly. "[But] the technology could be useful for giving women an additional four or five years of fertile lifespan." Another way to keep the biological clock ticking would be to stop eggs maturing in the first place, allowing them to remain in ovarian storage until women were ready to use them. "When you found a partner you wanted to have children with, you could concentrate all your reproductive [resources] at that time," says Trounson.

One factor that plays a role is antiMullerian hormone, or AMH. In mice, AMH is made by granulosa cells in the ovary, and puts a brake on the number of eggs selected to mature (New Scientist, I I November 2000, p 20). Axel Themmen and colleagues at Erasmus University in Rotterdam studied mice that lacked AMH. At four months old, the mice had three times as many growing follicles as normal mice. By the time they were 13 months old, the mutant mice had completely run out of eggs.

Themmen is now investigating how AMH works in humans. A drug that enhances its effects might one day become the basis for a new "career pill". But while research into career pills and anti-menopausal drugs is moving at a comfortable pace, techniques to improve pregnancy rates among women who are already running out of eggs are being unleashed at a speed that is causing some consternation, even in fertility circles. This is of particular concern in countries such as the US, where there is no direct federal government regulation of fertility treatments. 'There, the Food and Drug Administration strictly controls the testing of new drugs, while new medical technologies tend to be left to individual states to regulate. All too often, that means fertility doctors need only get consent from their patients and their clinic's own review board before they try out new techniques. Take cytoplasmic transfer, the highly controversial technique that creates children that carry the genetic material of three people. Jacques Cohen and Jason Barritt of the St Barnabas Medical Center in New jersey attracted international criticism for their work. Among fertility experts, the major worry is not about the few extra genes carried in the mitochondria-the cell's powerhouses that make up a fraction of the jelly-like cytoplasm-but about the wisdom of using the new technique in humans without testing whether it works.

'THE EGG IS NOT JUST A QUIESCENT LITTLE BLOB, THERE'S AN INCREDIBLE AMOUNT GOING ON'

One of the main problems older women face when trying to conceive is that their eggs often end up with the wrong number of chromosomes, a condition called aneuploidy. If an aneuploid egg is fertilised, the resulting embryo either miscarries-sometimes before the pregnancy is detected-or the child is born with a handicap such as Down's syndrome. One theory is that the cellular machinery in the cytoplasm that is needed to deal the right number of chromosomes into the two halves of the dividing egg is too old to do its job properly. That has led to the controversial notion that a shot of fresh cytoplasm from a younger woman's egg could also help when an older woman's eggs fail to produce babies for unknown reasons.

The trouble is, say critics like Winston and Trounson, there's no hard evidence that the technology helps women get pregnant. True, the women that Cohen and Barritt treated had had many failed IVF attempts before they got pregnant following the new procedure. And, true, their embryos looked better under a microscope than those they produced without the procedure-but who's to say that the same wouldn't have happened with just one more round of IVF? To find out, you would need to run trials that compared cytoplasmic transfer or IVF alone in women with the same history of infertility.

What's more, the few experiments testing similar techniques in animals have been contradictory. Even worse, the cytoplasm contains substances that are vital to the normal development of the embryo, so there's even a slim chance that cytoplasmic transfer may threaten the long-term health of the baby. Nothing is really known about the consequences of techniques like cytoplasmic transfer, says Tilly, who believes patient demand and doctors' willingness to comply with those demands is rushing new treatments into the clinics too quickly. After all, one in six couples have fertility problems and for them the treadmill of fertility treatments can seem like their only option (see "Right to choose", page 41) "Patients are driving a whole load of technologies that haven't been validated," he says.

In fact, the babies born after cytoplasmic transfer are all reportedly doing fine. But two of the 17 fetuses created by Cohen and Barritt had a chromosomal abnormality that causes a disorder called Turner syndrome and did not survive, although no one can say whether the technique is to blame.

Eggbert the mouse

What we do know is that animal experiments that involve manipulating eggs paint a disturbing picture. Take Eggbert the mouse, the only mammal created so far from an egg grown mainly in a lab-a feat that fertility doctors would dearly like to repeat with human eggs to reduce the need for egg donors , and slash the costs of IVF.

At birth Eggbert appeared normal enough, and even went on to father a few pups. But at six months, disaster struck. Eggbert became obese, developed neurological problems and eventually died. A post-mortem revealed that Eggbert suffered from some of the same defects that plague cloned animals (New Scientist, 19 May, p 14). "That's why we are so concerned. People should be very, very careful," says John Eppig, a reproductive biologist at The Jackson Laboratory in Maine who led the team that created Eggbert. "Simply having a baby's footprints at birth doesn't [necessarily] mean success."

Of course, the egg that became Eggbert was manipulated in a different way from the human eggs undergoing cytoplasmic transfer, but it illustrates a point. The egg 'is not just a quiescent little blob", says Kate Hardy, a reproductive biologist at Imperial College, London. "There's an incredible amount going on," most of which fertility researchers are only just beginning to understand.

Still not everyone is so quick to condemn the aggressive approach some infertility clinics take. "You'll hear that there's no regulation in the States-and that's not an accurate statement at all," says Sean Tipton, a spokesman for the American Society for Reproductive Medicine. 'What we don't regulate is people's reproductive choices." (The St Barnabas clinic wouldn't let Barritt talk to Ne,w Scientist, but sent a written statement saying that its research complied with the hospital's "stringent medical guidelines".) What's more, points out Tipton, similar criticisms were once levelled at IVF, an innovation that society now embraces. 'We don't know for a certain fact that every human being conceived through an IVF process is not going to drop dead at the age of 30. We don't know that because the first IVF baby is not that old yet. But there is certainly nothing to indicate that that's going to be a problem. If you insist on that sort of long-term outcome, you're never going to get anywhere."

But while fertility researchers struggle to balance the demands of science and their patients, one thing is clear: the number of patients is only going to grow. Women are delaying childbirth like never before-the average age for having a first child in Britain is now nearly 30-and without medical intervention a portion of those women are destined to swell the ranks of the infertile. Bridget Jones aside, the need for a safe way to slow down the biological clock has never been more urgent. F7

Further reading: "Alternative sources of gametes: reality or science fiction?" by Ming Tsai and others, Human Reproduction, vot 15, p 988 (2000) "Oocyte apoptosis is suppressed by disruption of the acid sphingomyetinase gene or by sphingosineI-phosphate therapy" by Yutaka Morita and others, Nature Medicine, vot 6, p 1109 (2000) "In vitro maturation of oocytes" by Kate Hardy and others, British Medical Bulletin, vot 56, p 588 (2001)

NS 11 Nov 2000 El Dorado revisited

FOCUS Next week a row is set to erupt that will rock the staid world of anthropology. Just what did happen to the Yanomami tribe?

THIRTY-TWO years ago, two American researchers carried thousands of doses of measles vaccine through the Amazonian rainforest to study the remote Yanomami people. This much of the story everyone can agree on. But whether this scientific duo were medical heroes or imperialistic villains is the basis of a fierce row that is brewing in the scientific community-and threatens to destroy anthropology's good name. In a book to be published in the US next week called Darkness in El Dorado: How scientists and journalists devastated the Amazon author Patrick Tiemey presents the case @at anthropologist Napoleon Chagnon of the University of Califomia, Santa Barbara, and the geneticist James Neel of the University of Michigan in Ann Arbor, who died this year, helped place "one of the Amazon basin's oldest tribes on the cusp of extinction", as the publisher's blurb puts it. The most sensational of the allegations is that Neel's use of measles vaccine unleashed a lethal epidemic among the Yanomami people that killed up to one in five of those who became infected. As rumours of the book's contents have

leaked out, many have rushed to defend the accused. The debate is likely to get even more heated next week at the American Anthropological Association's annual meeting in San Francisco, where the two sides will meet in a special forum. T'he way the hostilities have broken out before the book has even been published might make an interesting study for future anthropologists of the information age. In early September, two reviewers of the book, anthropologists Terry Turner of Comell University in New York and Leslie Sponsel of the University of Hawaii at Manoa, sent a confidential e-mail to Louise Lamphere and Don Brenneis, the president and president-elect respectively of the American Anthropological Association. It wamed them of the book's allegations and the unwelcome publicity it would bring to their profession. 'It was dynamith, it was a bomb and we knew it would cause a commotion," says Turner. Many of the allegations, they warned, would become public in October when an excerpt was scheduled for publication in The New Yorker magazine. Two weeks after the reviewers sent

their supposedly private e-mail, it was still zipping back and forth through cyberspace, and people with even remote connections to anthropology were getting copies forwarded to them. "I received four in one day from different comers of the world," says Susan Lindee, a historian at the University of Pennsylvania, Philadelphia. Turner and Sponsel say they don't know who leaked their message. As New Scientist went to press, crucial parts of the book appear to have been toned down in the version that wfll appear in the shops next week, compared with the proofs sent to reviewers. Chagnon says: "Tierney puts the most negative twist on virtually everything I did to the point of...implying motives I didn't have." Chagnon and Neel have attracted publicity before, but often of a more positive kind. Chagnon began his study of the then obscure Yanomami people in 1964, when he was still a graduate student. In his 1968 book Yanomamd: The fierce people, he depicts a culture where violence, hostility and even killing help enhance social status, challenging widely held notions of the natural peacefulness of humans. The book led to films by Chagnon and others and sold more than a millioncopies, becoming a

standard text for anthropology students. In 1968, Chagnon teamed up with Neel, who was already an eminent geneticist and doctor. When Neel died in February this year, Francis Collins of the US National Human Genome Research Institute said he was a pioneer who had "birthed the field of human genetics". Among his other distinctions, Neel had been in charge of the Atomic Bomb Casualty Commission, which among other things studied how the Japanese victims of Hiroshima and Nagasaki had been affected by exposure to radiation. For him, the Yanomami were a perfect control population, whose isolation guaranteed they had never been exposed to anything but background radiation. In addition, he wanted to observe their immunological response to a vaccine. The way in which the Yanomami's immune systems reacted to the weakened form of nwasles virus might also have given them valuable information about why measles proved so'deadly to isolated peoples. But when Chagnon and Neel arrived in the Amazon, they reported finding a measles epidemic already gathering momenttfm, possibly originating from other outside contacts. Tierney argues that the extreme isolation of the Yanomami would have made this unlikely In the final version of the book, Tiemey accuses Neel of recklessly selecting a vaccine that posed a higher risk of measles compared with other vaccines in order to test his theories that those higher up the social scale would be better at fighting disease. For his tests, Neel chose to use the Edmonston B measles vaccine, which contained a live, weakened form of the virus. Tierney argues that Edmonston B was a strangely dangerous choice, given that weaker strains of the vaccine were available and that most Yanomami had never been exposed to measles and were chronically sick and malnourished. Neel's defenders say Tierney's claims are wrong. The University of Michigan, in an extensive statement, calls the book the "literary equivalent of a professional 'hit'". It claims that Tiemey's book is the result of a long-standing professional vendetta by Chagnon's critics. They dismiss as absurd any notion that the researchers' activities created a climate of aggression in Yanomami society, since records of their violence date back to before Chagnon's birth. A,nd at least two of the scientists whom Tiemey quotes as quesfioning Neel's choice of the vaccine came to Neel's defence when contacted by New Scientist. Samuel Katz of Duke University in Durham, North Carolina, who helped develop the Edmonston B vaccine, says that it was approved and used on millions of children in the US and abroad until 1975, including some Who suffered as much from malaria and malnutrition as the Yanomami. And these children weren't able to transmit measles. "I might have made a different choice, but Neel's was also logical," says Yale University epidemiologist Francis Black, whom Tierney describes as reacting with disbelief when informed of Neel's use of Edmonston B. "It gave stronger adverse reactions, but was a better studied vaccine and was known to give immunity for ten years." Neither scientist recalled talking to Tierney, although both said they could have easily forgotten short telephone conversations. Tierney hasn't yet responded to these volleys. His publicist says that an agreement with his publisher prevents him from commenting on the book before its publication. The review proofs had only limited circulation, so most of the criticism of the book has been centred on the content of Turner and Sponsel's leaked e-mail and the extracts published in The New Yorker. Sponsel says the full scale of Tiemey's charges isn't yet understood. "So far, 95 per cent of the fight has been over the vaccine," says Sponsel. "But 95 per cent of the book is about other things." Both sides in the controversy agree that its implications extend beyond personal animosities. Critics of the book say it may make indigenous peoples suspicious of medical help and impede vaccination efforts around the world. Others say that if any of the allegations are true, then reparations should be paid to the Yanomami. Chagnon is considering legal action. With the publication of the book and the lifting of the gag on Tierney, a fuller analysis can begin. Whether or not his allegations are confirmed, they may inflict permanent damage on anthropology. Alternatively, they might help the science of anthropology to emerge all the stronger, with stricter ethical standards in place. The future of an entire field of study will be affected. Philip Cohen

AS THE Earth gets hotter, its biosphere may accelerate rather than slow global warming, climate modellers have found. Peter Cox and his colleagues at the Hadley Centre for Climate Prediction and Research at Bracknell have created the first climate model that includes constant interaction between vegetation, the atmosphere and the oceans. Trees, grass and shrubs are allowed to grow, die and breathe at rates that depend on envirom-nental factors, including temperature and atmospheric-CO, levels. The results are fed back into the simulation. Plants generally absorb more C02 as more is pumped into the atmosphere. But as it gets hotter, the amount absorbed by plants levels out, while the amount produced by microorganisms in the soil increases exponentially. This means that the biosphere has an overall warming effect as temperatures climb.

Drying and warming will also tum large areas of the Amazon rainforest into grassland, predicts Cox, further accelerating the effect (New Scientist, 6 May, p 7). The results from Cox's model are alarming. By 2050, he says, the biosphere will rapidly switch ftom sucking up a little C02 to belching out a lot. As a result, temperatures over land could increase by as much as 6' C, instead of the 40 predicted by other models. Those numbers show the vital role of the biosphere, says Cox. "Their model is pretty extreme," says Ian Woodward of the University of Sheffield, who cautions that other models don't show such a large dieback in the Amazon. "But," he says, "what they've got now is the best way forward." Nicola Jones

More at: Nature (9 November, p 184)

While the rich stay rich, the poor get hotter

THE Silk Road to Samarkand is hot and dusty-and the devastating droughts and searing heat of this part of central Asia are almost certain to get worse. In a blistering new analysis of global warming's winners and losers, climate scientists warn that temperatures in the region, which now regularly exceed 40 OC, are due for some of the biggest increases in the coming century. The study, from the newly founded Tyndall Centre for Climate Change Research at the University of East Anglia in Norwich, predicts that some countries will warm up more than twice as much as others during the coming century. As negotiators from more than 160 countries gather in The Hague this weekend to plan ways of curbing emissions of greenhouse gases, many will for the first time be armed with a detailed prediction of how their country will fare if nothing is done. The study predicts more than 5 'C of warming for a string of Asian countries, from Kazakhstan to Saudi Arabia, that are already among the hottest and driest in the world. Several, including Uzbekistan, Tajikistan, Afghanistan and Iran, have suffered famine this year. They are followed by other drought-ridden countries in West Africa. Mike Hulme, director of the centre, says: "What is critical about our report is that for the first time it shows individual countries how much warming to expect and how the burden of climate change will be distributed across the world." In line with previous predictions, the study confirms that the biggest temperature rises are likely to be in Russia and Canada, whose large Arctic territories are expected to be more ttian 6 OC warmer by the end of the 21st century. Some countries can look forward to global warming with more equanimity, at least as far as temperatures are concemed. The six nations set for the least warming, at around 3 'C or less, are Ireland and Britain in the northern hemisphere, and New Zealand, Chile, Uruguay and Argentina in the south. Hulme's study divided national wealth by the predicted temperature rise to assess the likely impact of warming on each country's population. The four most vulnerable countries by this measure are Afghanistan, Ethiopia, Sierra Leone and Tanzania. Each has only $100 of its GDP per inhabitant to cope with every degree of warming. The least vulnerable country is Luxembourg, with $8800 per capita for each degree of warming. Almost without exception, the nations that are most threatened by global warming produce the smallest amounts of greenhouse gases, says Hulme. But another leading climate scientist from the University of East Anglia questions Hulme's analysis. Developing nations need not be passive victims, says Nhck Kelly of the university's Climatic Research Unit. Many poor developing countries 'have developed a considerable capacity to cope and adapt" to climate threats such as floods and drought, he says. "It could be argued that the heavy dependence of the industrialised nations on technology untested against envirorunental trends means these nations are among the most susceptible to climate change." Fred Pearce

More at: wwwtyndall.uea.ac.uk

Your country needs you
Were 30,000 soldiers duped into testing deadly chemical weapons?

BRITAIN'S Ministry of Defence should allow an immediate study of the health risks facing survivors of chemical weapons tests it carried out until 1989, sak politicians and scientists. The demands follow the publication this week of Gassed, a book claiming that Britain deliberately exposed up to 30,000 servicemen to poison gases in the world's longestrunning programme of chemical warfare experiments. As New Scientist went to press Wiltshire police refused to confirm or deny reports that 40 deaths were now under investigation as a result of the tests. T'he author, joumahst Rob Evans, claims that many of the tests done secretly during the cold war broke the Nuremberg code of ethics, introduced in 1947 to avoid a repeat of the horrific experiments conducted in Nazi concentrafion camps during the Second World War. A spokeswoman for Porton Down says: "The actions were consistent with the standards of the day." She adds that 20,000 servicemen were exposed, not 30,000. [email protected] one leading expert on chemical warfare, chemical pathologist Alastair Hay of Leeds University, says nerve gas tests done at Porton Down "were ethically questionable and scientifically flawed because they failed to properly assess the risk. These experiments on servicemen failed to properly assess the risks. There is a huge question mark over whether their consent was really informed. You wouldn't get away with it today. " He says there should be a large-scale investigation into the health of survivors. Ian Gibson, a Labour MP on the House of Commons Select Committee on Science and Technology, backs Hay in calling for an investigation into the health effects and ethics of the experiments. 'I think people were conned into the tests," he says. Gibson wants MPs to visit Porton Down as soon as possible to quiz scientists there, and will raise the issue in the House of Commons this week. "It would be no surprise if people were suffering long-term health effects," he told New Scientist. "Porton Down needs independent scrutiny." The book is based on over 100 interviews with those who took part in and ran the experiments at the Porton Down chemical warfare research centre in Wiltshire, as well as dozens of previously confidential official reports. Evans cites government documents that show young soldiers were exposed to sub-lethal doses of mustard gas, nerve gas, tear gas and mind-bending drugs like LSD in numerous experiments at Porton Down. The aim was to find out about the toxicity of the gases, and many servicemen suffered illnesses as a result. In the early 1950s, the liquid nerve gases sarin, soman and GF were dripped on to the skin or clothes of 396 men. The experiment went disastrously wrong. Five men were admitted to hospital, one had to be revived after suffering respiratory failure, and one died. The death of 20-year-old airman Ronald Maddison is the subject of a murder investigation launched in August 1999 by Wiltshire police. Hay suggests a health survey should look for links with respiratory diseases and tumours. Men whose skin was exposed to mustard gas should be investigated for skin cancers. Those who took part in the nerve gas experiments risk damage to the nervous system, Hay says. This could include heart and muscular problems, as well as mood swings and depression. Britain is not alone in having conducted large-scale chemical weapons tests on people. But its 73-year testing programme was exceptionally large. In the US, only 15,000 people participated in chemical warfare experiments, and they were stopped after a public outcry in 1975. Tests on 2000 people were carried out in both Canada and Australia. Australia has awarded pensions to servicemen who took part in mustard gas experiments and then suffered serious illness. The volunteers at Porton Down have not received any such compensation. Rex Watson, a former director of Porton Down, has defended the experiments as ethical, given the threat that was posed by the Soviet Union during the cold war. Like many of his scienfific colleagues, he put himself forw;ird for tests alongside volunteers from the services. Rob Edwards

Eggs may live longer

DUTCH researchers have identified a hormone that may influence how quickly mammals use up their lifetime's supply of eggs. The hormone might one day be used to delay menopause to prevent conditions such as osteoporosis, or to extend a woman's fertile life. Axel Themmen and his colleagues at Erasmus University in Rotterdam were studying mice when they found that the substance, called anti-Mullerian hormone (AMH), puts the brakes on the early stages of follicle development. At one week old, baby mice have thousands of primordial follicles that are capable of developing into eggs. Over a mouse's lifetime, most of those follicles will start to develop. But whereas a few will go all the way and become mature eggs, the vast majority will die off before reaching that stage. AMH is best known for its role in male embryo development, but is also made by the granulosa cells that surround the growing follicles. This suggests that AMH helps keep the number of developing follicles at a constant level, says Themmen. At four months old, mice that lacked AMH had 3 times the number of growing follicles and fewer primordial follicles than normal mice, Themmen told the llth International Congress of Endocrinology in Sydney last week. But the mice that lacked the AMH brake used up their eggs quicker. Because there were no primordial follicles left in 13-month-old mice, says Themmen, there were no small growing follicles. If AMH inhibits the development of follicles in humans in the same way, it may be possible to use it as a drug to delay the menopause, says Ray Rodgers, a reproductive endocrinologist at Flinders University in Adelaide. "If we could make the reservoir of primordial follicles last until the end of a woman's life, we may be able to prevent menopause, and the osteoporosis and cardiovascular changes that follow," he says. MWbiting the follicle development could even help extend a woman's reproductive life by preventing eggs being used up dunng periods when she doesn't want to conceive, Rodgers speculates. Rachel Nowak, Melboume

PRIME TIME Fame and fortune await the person who cracks the greatest problem in mathematics. And that could be any day now, says Erica Klarroich

WHEN G. H. Hardy faced a stormy sea passage from Scandinavia to England, he took out an unusual insurance policy. Hardy scribbled a postcard to a friend with the words: "Have proved the Riemann hypothesis". God, Hardy reasoned, would not let him die in a shipwreck, because he would then be feted for solving the most famous problem in mathematics. He survived the trip. Almost a century later, the Riemann hypothesis is still unsolved. Its glamour is unequalled because it holds the key to the primes, those mysterious numbers that underpin so much of mathematics. And now whoever cracks it will find not only glory in posterity, but a tidy reward in this life: a $1 million prize announced this April by the Clay Mathematics Institute in Cambridge, Massachusetts. Th6re are signs that the great prize might soon be claimed, and the most promising approaches come not from pure mathematics, but from physics. Researchers have discovered a deep connection between the Riemann hypothesis

and the physical world-a connection that could not only prove the hypothesis, but also tell us something profound about the behaviour of atoms, molecules and even concert halls. One mathematician has followed this lead into a very strange place, seeking a solution in an intricately twisted space with infinitely many dimensions. Yet the primes seem simple enough at first glance. They are those numbers, like 2, 3, 5 and 7, that are only divisible by 1 and themselves, although 1 isn't included among them. Primes are the atoms of the number system, because every other number can be built by multiplying primes together. Unfortunately there is no periodic table for the primes-they are maddeningly unpredictable, and finding new primes is mostly a matter of trial and error. In the 19th century, mathematicians found a little order ib this apparent chaos. Even though individual primes pop up unexpectedly, their distribution follows a trend. It's like tossing a coin. The result is unpredictable, but after many coin tosses we expect roughly half heads and half tails. The primes get rarer as you look at larger and larger numbers (see Diagram, p 36), and mathematicians found that this thinning out is predictable. Below a given number X, the proportion of primes is about 1 lln(x), where ln(x) is the natural logarithm of x. So, for example, about 4 per cent of numbers smaller than ten billion are prime. So far so good. But that "about' is very vague. Numbers are products of pure logic, and so surely they ought to behave in a precise, regular way. Mathematicians would at least like to know how far the prime numbers stray from the distribution. Georg Riemann found a vital clue. In 1859, he discovered that the secrets of the primes are locked inside something called the zeta function. The zeta function is simply a particular way of turning one number into another number, like the function "multiply by 5". Riemann decided to see what would happen if he fed the zeta function complex numbersnumbers made from a real part (an ordinary number) and a so-called imaginary part (a multiple of i, the square root of -1). Complex numbers can be visualised as arrayed on the complex plane, with real numbers on the horizontal axis and imaginary numbers on the vertical axis.

Riemann found that certain complex numbers, when plugged into the zeta function, produce the result zero. The few zeros he could calculate lay on a vertical line in the complex plane, and he guessed that, except for a few well-understood cases, all the infinity of zeros should lie exactly on this line. What does this have to do with the primes? If you plot how many primes exist below a given number (see Diagram, p 36), what you get is a smooth curve with small wiggles added-that is, the 1/ln(x) rule, plus deviations. According to Michael Berry of Bristol University, you can think of that pattem of deviations as a wave. just like a sound wave, it is made up of many frequencies. "And what are the frequencies?" asks Berry. "They're the Riemann zeros. The zeros are harmonies in the music of the primes.Berry isn't speaking in metaphors. 'I've tried to play this music by putting a few thousand primes into my computer," he says "but it's just a horrible cacophony. You'd actually need billions or trfllionssomeone with a more powerful machine should do it." Riemann worked out that if the zeros really do lie on the critical line, then the primes stray from the 1 lln(x) distribution exactly as much as a bunch of coin tosses stray from the 50:50 distribution law. This is a startling conclusion. The pri-Tnes aren't just unpredictable, they really do behave as if each prime number is picked at random, with the probability I /in(x)-ahnost as if they were chosen with a weighted coin. So to some extent the primes are tamed, because we can make statistical predictions about them, just as we can about coin tosses. But only if Riemann's guess was right. If the zeros don't line up, then the prime numbers are much more unruly. As Enrico Bombieri of the Institute for Advanced Study in Princeton writes on the Clay Institute website (wwwclay math.org/prize-problems/riemann.htm): "The failure of the Riemann hypothesis would create havoc in the distribution of prime numbers." And the havoc would spread further. Hundreds of results in number theory begin, "If the Riemann hypotht-sis is true, then. . ." This is why mathematicians long to prove the hypothesis. But how do you prove something about an infinity of numbers? Researchers have used supercomputers to calculate the first 1,500,000,001 zeros above the x-axis, and millions of other zeros higher up, and so far all of them lie on the critical line. If just one of them did not, the Riemann hypothesis would be killed. This is heartening, but no amount of computer hacking can prove the hypothesis. There are always more zeros to check. And, cautions Andrew Odlyzko of AT&T Labs, who has spearheaded the effort to calculate zeros, "number theory has many examples of conjectures that are plausible, are supported by seemingly overwhelming numerical evidence, and yet are false." Some deeper insight is needed. Early in the 20th century, mathematicians made a daring conjecture: that the Riemann zeros could correspond to the energy levels of a quantum mechanical system. Quantum mechanics deals with the behaviour of tiny particles such as electrons. Crucially, its equations work with complex numbers, but the energy of a physical system is always measured by a real number. So energy levels form an infinite set of numbers lying along the real axis of the complex plane-a straight line. This sounds like Riemann's zeros. The line of zeros is vertical, rather than horizontal, but it is a simple bit of maths to rotate it and put it on top of the real hne. If the zeros then match up with the energy levels of a quantum system, the Riemann hypothesis is proved. For decades, this ide@ was only wishful thinking. Then in 1972 came a hint that it could work. Hugh Montgomery, at the University of Michigan, had found a formula for the spacings between Riemann zeros. Visiting the Institute for Advanced Study at Princeton, he ran into physicist Freeman Dyson at aftemoon tea, and mentioned his formula. Dyson recognised it immediately. It was identical to a formula that gives the spacings between energy levels in a category of quantum systems-quantum chaotic systems, to be precise. Chaos theory applies to physical systems so sensitive to their starting conditions that they are impossible to predict. In the Earth's chaotic atmosphere, for example, the tiny draught caused by the flap of a butterfly's wings can eventually lead to a tremendous storm. Almost all complicated systems are chaotic. The quantum versions of these systems have a jumble of energy levels, scattered apparently at random but in fact spaced according to Montgomery's formula. Quantum chaotic systems include atoms bigger than hydrogen, large atomic nuclei, all molecules, and electrons trapped in the microscopic arenas called quantum dots. Could the Riemann zeros fit one of these quantum chaofic systems? In the late 1980s, Odlyzko picked an assortment of systems, and compared their energy levels with the Riemann zeros. In a discovery that electrified mathematicians and physicists, Odlyzko found that when he averaged out over many different chaotic systems, the energy level spacings fitted the Riemann spacings with stunning precision. That's still not enough. To prove the Riemann hypothesis, researchers must pinpoint a specific quantum system whose energy levels correspond exactly to the zeros, and prove that they do so all the way to infinity. Which, of all the different systems, is the right one? Berry and his colleague Jonathan Keating have made one suggestion. In a chaotic system, an object usually moves unpredictably, but sometimes its path will cycle back on itself in a "periodic orbit". Berry and Keating think that the right quantum system will have an infinite collection of periodic orbits, one for each prime number. And last year, Nicholas Katz and Peter Samak predicted that the system should have a special kind of symmetry called symplectic syrrunetry. Both of these clues should help quantum chaologists zero in on the one system that will prove the Riemann hypothesis. "I have a feeling that the hypothesis will be cracked in the next few years," says Berry. "l see the strands coming together. Someone will soon get the million dollars." The winner could well be Alain Connes, a mathematician based at the Institute of Advanced Scientific Study in Bures-surYvette, France. Connes has a startlingly direct approach to the problem: create a system that already includes the prime numbers. To understand how, you have to imagine a quantum system not as a particle bouncing around an atom, say, but as a geometrical space. It sounds odd, but it represents one of the weird things about quantum systems: they can be two or more things at once. Like Schr6dinger's cat, which is a peculiar mixture of dead and alive, any quantum object can find itself in a .superposition" of different states. To characterise this messy existence, physicists use what they call a state space. For each kind of possibility (say "alive" and 'dead"), you draw a new axis and add a dimension to the space. If there are just two possible states, as is the case for Schr6dinger's cat, the space is two dimensional, with three states it is three dimensional, and so on. Then in the Schrbdinger's cat space, you would mark a cross one unit along the x-axis to represent a fully alive cat. Similarly, a stone dead cat would be one unit up the y-axis, and a part-alive, partdead cat would appear @omewhere along an arc between these points. The 'shape" of the space affects how the state moves around in it, and therefore how the system works, including the way its energy levels are arrayed. This depends not just on the number of dimensions, but also on the geometry of how they are stuck together. Connes decided to build a quantum state space out of the prime numbers. Of course, the primes are a bunch of isolated numbers, nothing hke the smooth expanses of space in which we can measure @gs like angles and lengths. But mathematicians have invented some bizarrely twisted geometries that are based on the primes.

'Right now, when we tackle problems without knowing the truth of the Riemann hypothesis, it's as if we have a screwdriver. But when we have it, it'll be more like a bulldozer'

In "5-adic" geometry, for example, numbers far apart (in the ordinary way) are pulled close together if they differ by 5, or 15, or 250-any multiple of 5. In the same way, 2-adic geometry pulls together all the even numbers. To put all the primes in the mix, Connes constructed an infinite-dimensional space called the Adeles. In the first dimension, measurements are made with 2-adic geometry, in the second dimension with 3-adic geometry, in the third dimension with 5-adic geometry, and so on, to include all the prime numbers. Last year Connes proved that his primebased quantum system has energy levels corresponding to all the Riemann zeros that lie on the critical line. He will win the fame and the million-dollar prize if he can make one last step: prove that there aren't any extra zeros hanging around, unaccounted for by his energy levels. That last step is a formidable one. Has Connes simply replaced the Riemann hypothesis with an equally difficult question? Some experts advise caution. "I still think that some major new idea is needed here," says Bombieri. Berry, for his part, doesn't flinch at the mathematical peculiarity of Connes's system. "I'm absolutely sure that if he's right, someone will find a clever way to make it in the lab. Then you'll get the Riemann zeros out just by observing its spectrum." Berry and Keating are now turning around this connection with physics, using mathematics based on the Riemann zeta function to predict the behaviour of chaotic systems. Most models of quantum chaos are complicated and difficult to calculate. The Riemann zeros, by comparison, are easy to compute. "We always test our formulae on the Riemann zeta function to see if they work," says Keating. If Connes or one of the physicists proves the Riemann hypothesis using a quantum system, the link will be firmly established. Then, Berry predicts, the field will blossom. Using the mathematics of the zeta funcfion, scientists will be able to predict the scattering of very high energy levels in atoms, molecules and nuclei, and the fluctuations in the resistance of quantum dots in a magnetic field. And it turns out that the same mathematics applies to any situation wher@ waves bounce around chaotically, including light waves and sound. So the performance of microwave cavities and fibre optics could be improved, and the acoustics of real concert halls might profit from the music of the primes. Even so, it is mathematics that will gain the most. 'Right now, when we tackle problems without knowing the truth of the Riemann hypothesis, it's as if we have a screwdriver," says Samak. "But when we have it, it'll be more like a bulldozer." For example, it should lead to an efficient way of deciding whether a given large number is prime. No existing algorithms designed to do this are guaranteed to terminate in a finite number of steps. Proving the Riemann hypothesis won't be the end of the story. It will prompt a sequence of even harder, more penetrating questions. Why do the primes achieve such a delicate balance between randomness and order? And if their pattems do encode the behaviour of quantum chaotic systems, what other jewels will we uncover when we dig deeper? Those who believe that mathematics holds the key to the Universe might do well to ponder a quesfion that goes back to the ancients: What secrets are locked within the primes? Fl

Erica Klarroich is a mathematician and science writer based in Santa Cruz, Califomia

Further reading:www.utm.edu/research/primes www.ams.org/new-in-math/cover/pdme-chaos.htmi

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