The Origin of Menopause: Why Do Women Outlive Fertility?

New research sheds light on why women survive for decades when females in many other species die after they lose the ability to reproduce.

By Tabitha M. Powledge

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."

China's Three Gorges Dam: An Environmental Catastrophe?

March 25, 2008 spacer

Even the Chinese government suspects the massive dam may cause significant environmental damage

By Mara Hvistendahl


DAM THE ENVIRONMENT: Has an environmental cataclysm been unleashed by China's Three Gorges Dam?

SHANGHAI—For over three decades the Chinese government dismissed warnings from scientists and environmentalists that its Three Gorges Dam—the world's largest—had the potential of becoming one of China's biggest environmental nightmares. But last fall, denial suddenly gave way to reluctant acceptance that the naysayers were right. Chinese officials staged a sudden about-face, acknowledging for the first time that the massive hydroelectric dam, sandwiched between breathtaking cliffs on the Yangtze River in central China, may be triggering landslides, altering entire ecosystems and causing other serious environmental problems—and, by extension, endangering the millions who live in its shadow.

Government officials have long defended the $24-billion project as a major source of renewable power for an energy-hungry nation and as a way to prevent floods downstream. When complete, the dam will generate 18,000 megawatts of power—eight times that of the U.S.'s Hoover Dam on the Colorado River. But in September, the government official in charge of the project admitted that Three Gorges held "hidden dangers" that could breed disaster. "We can't lower our guard," Wang Xiaofeng, who oversees the project for China's State Council, said during a meeting of Chinese scientists and government reps in Chongqing, an independent municipality of around 31 million abutting the dam. "We simply cannot sacrifice the environment in exchange for temporary economic gain."

The comments appeared to confirm what geologists, biologists and environmentalists had been warning about for years: building a massive hydropower dam in an area that is heavily populated, home to threatened animal and plant species, and crossed by geologic fault lines is a recipe for disaster.

Among the damage wrought: "There's been a lot less rain, a lot more drought, and the potential for increased disease," says George Davis, a tropical medicine specialist at The George Washington University (G.W.) Medical Center in Washington, D.C., who has worked in the Yangtze River Basin and neighboring provinces for 24 years. "When it comes to environmental change, the implementation of the Three Gorges dam and reservoir is the great granddaddy of all changes."

Dam Quake
When plans for the dam were first approved in 1992, human rights activists voiced concern about the people who would be forced to relocate to make room for it. Inhabited for several millennia, the Three Gorges region is now a major part of western China's development boom. To date, the government has ordered some 1.2 million people in two cities and 116 towns clustered on the banks of the Yangtze to be evacuated to other areas before construction, promising them plots of land and small stipends—in some cases as little as 50 yuan, or $7 a month—as compensation.

Chinese and foreign scientists, meanwhile, warned that the dam could endanger the area's remaining residents. Among their concerns: landslides caused by increased pressure on the surrounding land, a rise in waterborne disease, and a decline in biodiversity. But their words fell on deaf ears. Harnessing the power of the Yangtze has been a goal since Nationalist leader Sun Yat-sen first proposed the idea in 1919. Mao Zedong, the father of China's communist revolution, rhapsodized the dam in a poem. The mega- project could not be realized in his lifetime, however, because the country's resources were exhausted by the economic failures of the Great Leap Forward in the late 1950s and then the social upheaval of the Cultural Revolution from the mid-1960s a to the early 1970s. Four decades later, the government resuscitated Mao's plans. The first of the Yangtze's famed gorges—a collection of steep bluffs at a bend in the river—was determined to be the perfect site.

In June 2003, nine years after construction began, the state-owned China Yangtze Three Gorges Development Corporation (CTGPC) filled the reservoir with 445 feet (135 meters) of water, the first of three increments in achieving the eventual depth of 575 feet (175 meters). The result is a narrow lake 410 miles (660 kilometers) long—60 miles (97 kilometers) longer than Lake Superior—and 3,600 feet (1,100 meters) wide, twice the width of the natural river channel. Scientists' early warnings came true just a month later, when around 700 million cubic feet (20 million cubic meters) of rock slid into the Qinggan River, just two miles (three kilometers) from where it flows into the Yangtze, spawning 65-foot (20-meter) waves that claimed the lives of 14 people. Despite the devastating results, the corporation three years later (in September 2006) raised the water level further—to 512 feet (156 meters). Since then, the area has experienced a series of problems, including dozens of landslides along one 20-mile (32-kilometer) stretch of riverbank. This past November, the ground gave out near the entrance to a railway tunnel in Badong County, near a tributary to the Three Gorges reservoir; 4,000 cubic yards (3,050 cubic meters) of earth and rock tumbled onto a highway. The landslide buried a bus, killing at least 30 people.

Fan Xiao, a geologist at the Bureau of Geological Exploration and Exploitation of Mineral Resources in Sichuan province, near several Yangtze tributaries, says the landslides are directly linked to filling the reservoir. Water first seeps into the loose soil at the base of the area's rocky cliffs, destabilizing the land and making it prone to slides. Then the reservoir water level fluctuates—engineers partially drain the reservoir in summer to accommodate flood waters and raise it again at the end of flood season to generate power—and the abrupt change in water pressure further disturbs the land. In a study published in the Chinese journal Tropical Geography in 2003, scholars at Guangzhou’s South China Normal University predicted that such tinkering with the water level could trigger activity in 283 landslide-prone areas.

That is apparently what happened to the 99 villagers of Miaohe, 10 miles (17 kilometers) upstream of the Yangtze, who saw the land behind their homes split into a 655-foot- (200-meter-) wide crack last year, soon after the reservoir water level was lowered for the summer floods. Officials evacuated them to a mountain tunnel where they camped for three months.

One of the greatest fears is that the dam may trigger severe earthquakes, because the reservoir sits on two major faults: the Jiuwanxi and the Zigui–Badong. According to Fan, changing the water level strains them. "When you alter the fault line's mechanical state," he says, "it can cause fault activity to intensify and induce earthquakes."

Many scientists believe this link between temblors and dams—called reservoir-induced seismicity—may have been what happened at California's Oroville Dam, in the foothills of the Sierra Nevada. The largest earthen dam in the U.S., it was constructed on an active fault line in the 1950s and filled in 1968. Seven years later, when the reservoir's water supply was restored to full capacity—after engineers lowered it 130 feet (40 meters) for maintenance—the area experienced an unusual series of earthquakes. U.S. Geological Survey seismologists subsequently found a strong link between the quakes and the refilling of the reservoir.

The Oroville area was sparsely populated, so little damage was done. But earthquakes have also been connected to past hydropower projects in China, where dams are often located in densely populated and seismically active river basins. Engineers in China blame dams for at least 19 earthquakes over the past five decades, ranging from small tremors to one near Guangdong province's Xinfengjiang Dam in 1962 that registered magnitude 6.1 on the Richter scale—severe enough to topple houses.

Surveys show that the Three Gorges region may be next. Chinese Academy of Engineering scholar Li Wangping reports on the CTGPC's Web site that the area registered 822 tremors in the seven months after the September 2006 reservoir-level increase. So far, none have been severe enough to cause serious damage. But by 2009, the dam's water level is set to be raised to its full 575-foot capacity and then lowered about 100 feet (30 meters) during flood season. That increase in water pressure, in water fluctuation and in land covered by the reservoir, Fan says, makes for a "very large possibility" that the situation will worsen.

Local news media report that whole villages of people relocated to make room for the dam will have to move a second time because of the landslides and tremors, indicating that officials failed to foresee the full magnitude of the dam's effects. Guangzhou's Southern Weekend late last year reported that villagers in Kaixian County were eager to move again, citing landslides, mudslides and ominous cracks that had appeared in the ground behind their homes. They also hoped that moving might resolve land allocation issues: Some said they received only half of the acreage they had been promised.

Water Displacement
The dam is also taking a toll on China's animals and plants. The nation—which sprawls 3.7 million square miles (9.6 million square kilometers)—is home to 10 percent of the world's vascular plants (those with stems, roots and leaves) and biologists estimate that half of China's animal and plant species, including the beloved giant panda and the Chinese sturgeon, are found no where else in the world. The Three Gorges area alone accounts for 20 percent of Chinese seed plants—more than 6,000 species. Shennongjia, a nature reserve near the dam in Hubei province, is so undisturbed that it is famous for sightings of yeren, or "wild man"—the Chinese equivalent of "Big Foot"—as well as the only slightly more prosaic white monkey.

That biodiversity is threatened as the dam floods some habitats, reduces water flow to others, and alters weather patterns. Economic development has spurred deforestation and pollution in surrounding provinces in central China, endangering at least 57 plant species, including the Chinese dove tree and the dawn redwood. The reservoir created by Three Gorges dam threatens to flood the habitats of those species along with over 400 others, says Jianguo Liu, an ecologist at Michigan State University and guest professor at the Chinese Academy of Sciences who has done extensive work on biodiversity in China.

The dam further imperils delicate fish populations in the Yangtze. Downstream, near where the river empties into the East China Sea, the land around the Yangtze contains some of the densest clusters of human habitation in the world, and overfishing there has already endangered 25 of the river's 177 unique fish species. According to a 2003 letter to Science by Wuhan University ecologist Ping Xie, many of these fish evolved over time with the Yangtze flood plain. As the dam decreases flooding downstream, it will fragment the network of lakes around the middle as well as lower the Yangtze's water level, making it difficult for the fish to survive. The project has already contributed to the decline of the baiji dolphin, which is so rare that it is considered functionally extinct.

The reservoir could also break up land bridges into small islands, isolating clusters of animals and plants. In 1986, Venezuela's Raúl Leoni Dam flooded 1,660 square miles (4,300 square kilometers) of land, creating the vast Lake Guri, along with a scattering of nonsubmerged land. The nascent islands lost 75 percent of their biological species within 15 years, according to research published in Science.

To determine the true toll, the Three Gorges Dam is taking on animal and plant species, Liu says, long-term data is needed, so that decreases in population totals can be compared with natural species fluctuation. But he cautions that many of the dam's effects may not be immediately apparent. The project is altering reproduction patterns, meaning it may already be too late for some plants and animals. "In the short term, you see the species still there, but in the long term you could see [them] disappear," Liu says. It is here that State Council representative Wang's allusion to "hidden dangers" rings especially true.

Disease and Drought
When officials unveiled plans for the dam, they touted its ability to prevent floods downstream. Now, the dam seems to be causing the opposite problem, spurring drought in central and eastern China. In January, the China Daily (the country's largest English-language newspaper) reported that the Yangtze had reached its lowest level in 142 years—stranding dozens of ships along the waterway in Hubei and Jiangxi provinces. An unnamed official with the Yangtze River Water Resources Commission blamed climate change, even as he acknowledged that the dam had reduced the flow volume of the river by 50 percent. To make matters worse, China is now plowing ahead with a controversial $62-billion scheme to transfer water from the Yangtze to northern China, which is even more parched, through a network of tunnels and canals to be completed by 2050.

Meanwhile, at the mouth of the Yangtze residents of Shanghai, China's largest city, are experiencing water shortages. The decreased flow of fresh water also means that saltwater from the East China Sea now creeps farther upstream. This, in turn, seems to be causing a rise in the number of jellyfish, which compete with river fish for food and consume their eggs and larvae, thereby threatening native populations that are already dwindling as a result of overfishing. In 2004, a year after the dam was partially filled, scientists noted a jellyfish species in the Yangtze that had previously only reached the South China Sea.

The effects of the dam's disturbance of whole ecosystems could reverberate for decades. G.W.'s Davis is part of a project researching the disease schistosomiasis (a.k.a. snail fever or swimmer's itch), a blood parasite transmitted to humans by snails; people can get it by swimming or wading in contaminated fresh water when infected snails release larvae that can penetrate the skin. (Symptoms include fever, appetite and weight loss, abdominal pain, bloody urine, muscle and joint pain, along with nausea, a persistent cough and diarrhea.) The snails used to breed on small flood plain islands where annual flooding prevented a population explosion. Now, the decreased flow downstream from the dam is allowing the snails to breed unchecked, which has already led to a spike in schistosomiasis cases in some areas.

According to Davis, such alterations could precipitate a rise in other microbial waterborne diseases as well. "Once you dramatically change the climate and change water patterns, as is now seen in the Three Gorges region," he says, "you change a lot of environmental variables. Almost all infectious diseases are up for grabs."

The official recognition of the dam's dangers suggests that the project's environmental and public health impacts are starting to sink in. Political analysts speculate that President Hu Jintao and Premier Wen Jiabao are eager to distance themselves from a project they inherited. Although halting plans at this point would be an admission of government error, the openness following the Chongqing meeting raised the hopes of worried scientists that officials would take action to minimize the project's environmental and public health fallout.

Government-funded institutions have been quietly assessing possible recourses. Officials say they've spent more than $1.6 billion on fortifying landslide-prone areas and will spend an additional $3.2 billion on water cleanup over the next three years. In January the CTGPC signed a memorandum of understanding with the Nature Conservancy allowing that organization to consult on species protection and river health in the dam area. China's Ministry of Health, meanwhile, is trying to control schistosomiasis infections with a combination of drugs and applications of molluscicides, pesticides that wipe out the disease's snail carriers.

But these measures may not be sufficient to avert disaster. In February China's State Environmental Protection Administration said reservoir water quality targets had not been reached despite a cleanup effort that had been underway since 2001. And fighting schistosomiasis requires a more holistic, multi-pronged approach—particularly now that ecosystems in the Three Gorges region have been altered. To ward off an outbreak, Davis says, the government would have to prevent the use of night soil as fertilizer, build cement irrigation ditches, and ensure area villagers access to clean water. So far, that hasn't happened.

Government Oversight
In the wake of media reports about the government's concerns, officials began to backpedal. In a November 2007 interview with state news agency Xinhua, State Council's Wang claimed that "no major geological disasters or related casualties" had occurred since the reservoir's water level was raised in 2006; five days later, the earth in Badong crumbled and the railroad tunnel landslide wiped out the bus and its passengers.

Following a brief period of openness, discussion of the dam's environmental effects has once again become largely taboo in China. Government officials fear that continued free discussion of the project's ramifications could lead to civil unrest. One internationally published Chinese scientist working in the Yangtze Basin declined to comment publicly, noting, "This is a very sensitive topic…. I can't give hypotheses."

Despite the Three Gorges dam's growing list of problems, however, hydropower remains an integral—and ostensibly green—component of China's energy mix. China still draws 82 percent of energy from coal, but large dams are crucial to the country's climate change program, which aims to increase its proportion of electricity from renewable resources from the current 7.2 percent to 15 percent by 2020. Over one third of that will come from hydropower—more than from any other source. Twelve new dams are planned for the upper Yangtze alone.

The logistical and environmental hurdles involved in executing these dams underscore China's commitment to hydropower. The Yangtze's newest dams include several smaller projects that are necessary to alleviate sedimentation caused by the Three Gorges reservoir. In his 2007 report to the National People's Congress, Prime Minister Wen Jiabao said that China had relocated 22.9 million people to make room for its large hydroprojects.

China's original goal was to fill the reservoir to its maximum level by 2013. Despite all the trouble, that target was moved up to 2009, Fan says, to boost hydropower output by an additional 2.65 billion kilowatt-hours each year.

"For the economic interests and profit of the Three Gorges Project Development Corporation," he says, "that's very important. But the function of any river, including the Yangtze, is not only to produce power. At the very least, [a river] is also important for shipping, alleviating pollution, sustaining species and ecosystems, and maintaining a natural evolutionary balance."

"The Yangtze doesn't belong to the Three Gorges Project Development Corporation," Fan adds. "It belongs to all of society."

Strange but True: Whale Waste Is Extremely Valuable

April 26, 2007

According to the ancients, parfumeurs and Arab royalty, the old saying might as well go: "Worth its weight in whale waste"

By Cynthia Graber

	Image: © AMBERGRIS.CO.NZ
	VALUABLE JUNK: It may look like a rock weathered by the sea, but it is actually ambergris which, depending on age, can sell for thousands of dollars.

A ten-year-old vacationing in Wales stumbles across a lump worth nearly $6,000. A 67-year-old New York native receives a candlelike rock in the mail from her 80-year-old sister and discovers she may be $18,000 richer. All because a whale had a bit of indigestion.

That upset stomach creates ambergris, a rare substance that has been highly valued for thousands of years as an ingredient in perfume and pharmaceuticals. Ambergris originates in the intestines of male sperm whales after they dine on squid, whose hard, pointy beaks abrade the whales' innards. Scientists believe that the whales protect themselves by secreting a fatty substance in their intestines to surround the beaks. Eventually the animals cast out a huge lump, up to hundreds of pounds at a time.

But don't refer to it as "whale vomit"; scientists postulate that whales do not expel ambergris through their mouths. No one has ever seen a sperm whale excrete ambergris, although sperm whale expert Hal Whitehead of Dalhousie University in Halifax, Nova Scotia, admits that it is assumed the voiding takes place as fecal excretion, because when first cast out, he says, "Well, it smells more like the back end than the front."

Viscous, black, stinky blocks of freshly expelled ambergris float on the ocean's surface. Sun, air and salt water oxidize the mass, and water continually evaporates. It hardens, breaks into smaller chunks and eventually becomes grey and waxy, embedded with small black squid beaks. The weathered chunks exude a sweet, earthy aroma likened to tobacco, pine or mulch. The quality—and value—of any given chunk depend on how much time it had spent floating or otherwise aging, says expert ambergris broker Bernard Perrin, because "it ages like fine wine."

For thousands of years this sea treasure has been highly prized. Middle Easterners historically powdered and ingested it to increase strength and virility, combat heart and brain ailments, or to spice food and drink. The Chinese called it "dragon's spittle fragrance." Ancient Egyptians burned it as incense. A British medical treatise from the Middle Ages informs readers that ambergris can banish headaches, colds and epilepsy, among other ailments. And the Portuguese took over the Maldives in the sixteenth century in part to gain access to the island's rich bounty of the redolent stuff.

Image: © DENIS SCOTT/CORBIS
AMBERGRIS FACTORY: Because ambergris cannot be synthesized yet, sperm whales remain the only producers thanks to a diet heavy in sharp squid beaks.

The Arabic anbar refers to this very whale-based substance and is the root of the word amber. Centuries ago the French employed amber gris and amber jaune (gray amber and yellow amber) to distinguish between animal-based ambergris and what today has become the standard meaning: the golden-hued vegetal resin.

Like other animal-based perfume components (such as musk) ambergris has a scent all its own—derived from its chemical component ambrein—that it imparts to popular perfumes such as Chanel No. 5. It also enriches the other olfactory notes of a perfume, much as salt enhances flavors and spices, and, most importantly, it prolongs a perfume's other scents. As odor chemist George Preti of the Monell Chemical Senses Center in Philadelphia explains, ambergris molecules are lipophilic (fat-loving), as are perfume molecules, but the ambergris molecules are larger and heavier. "The odor molecules have a high affinity for the other lipophilic molecules, so they stay associated with the ambergris molecules and don't go into the vapor phase all at once," Preti says.

American perfume companies no longer mix ambergris into their fragrances, most likely because of confusing legalities surrounding its sale here. Internationally, however, the trade is legal and Perrin has no problem finding French perfume companies to buy his stock. "We also sell it to a royal family in the Middle East and they use it as an aphrodisiac. Apparently they take some milk, some honey, and grind up small quantities of the amber and put that in as well," he says.

Many aspects of ambergris remain a mystery. Why is ambergris more commonly found in the southern hemisphere, though sperm whales range all the world's seas? Why is it only sperm whales—and particularly male sperm whales—that create it? How did ancient Middle Easterners decide to start using it for medicine, or decide that "eau de whale" would be a compelling fragrance?

Some, but not all, scent qualities of ambergris have been synthesized, so the original remains valuable. With sperm whale numbers down from the 1.1 million estimated prior to whaling to approximately 350,000 today, less ambergris floats on the seas. Still, Whitehead says the population is slowly recovering, and even though most findings turn out to be rocks or wax or other ocean detritus, beachcombers and fishermen continue to scour the sands and waves in hope of stumbling across a weathered chunk of this sea gold.

Good Sex Is Not a Rat Race

By David Dobbs
For years the story on rat sex has been this: the male seeks above all else to ejaculate quickly, and once he has done it with one female, he is eager to move on to new partners. The female, meanwhile, seeks to extend the sex encounter through "pacing." A new study finds that if pacing is slow enough, the male will prefer that familiar partner to someone new. The wait, it seems, makes the female more attractive.

"It's an awful lot like what we were taught in high school," says Concordia University psychologist James Pfaus, who co-authored the study with Nafissa Ismail, the graduate student who conceived it.

The experiment made innovative use of standard research devices called pacing chambers, which are cages with dividers having either one or four holes big enough to let a female rat through but too small for the larger male. Thus, the female can join or leave the male, allowing her to significantly lengthen her arousal and, studies have shown, her chance of pregnancy. But the mating rituals last longer in the one-hole chambers, because the male, eager to get at the female, often sticks his big head in the hole, blocking her only passage back to his side and delaying her return.
The researchers let 20 couples mate in one-hole chambers and 20 in four-hole chambers. Then they placed each couple, along with a novel female, in a larger, open area. Among males from four-hole chambers, about half preferred their familiar mates. Among males who mated more slowly in the one-hole chambers, 80 percent preferred the familiar partner.

Driving this behavioral dynamic is, as always with rat sex, some neurochemical reward. Boston University biologist Mary Erskine notes that "sexual preferences come from chemical rewards, and we can be sure there are some here." Sexual climax, in fact, unleashes a flood of pleasure-producing hormones and neurotransmitters, such as testosterone and dopamine. Pfaus speculates that the higher level of arousal created by the longer wait generates a stronger release, and a more substantial reward, thereby enforcing the preference.

"Whether it's simply a stronger dose of the usual chemical rewards or some in addition, we don't know," Pfaus says. "But something is making this sort of mating more rewarding to the male or rewarding in a different way."

Brilliant Whiteness of Strange Beetle Explained

Forget bleach: this bug may be the key to whiter whites

By JR Minkel

Image: COURTESY OF PETE VUKUSIC/EXETER UNIVERSITY WHITE AS A BEETLE: An unusually white beetle sports a bright color despite having extremely thin scales compared with other white materials. Your walls, clothes and teeth not white enough for you? Good news: scientists have identified the source of the dazzling whiteness of a beetle called Cyphochilus, and harnessing that knowledge could help make everything from paints to t-shirts more blindingly white. It turns out that the bug's scales contain a porous network of random protein fibers that scatter all wavelengths of light strongly, the prerequisite for an intense white color. The beetle might not stand out against the brilliant blue of a butterfly, but "in terms of sheer design ingenuity, for me this is my favorite," says optical physicist Pete Vukusic of Exeter University in England, who has studied the bright coloring of dragonflies and butterflies.

Vukusic knew he was on to something when he saw Cyphochilus on an insect collector's Web site. "Something this amazingly bright and white had to be coming from something very thin," meaning its thin coat of scales, he says. "That in itself is quite interesting. Any industry can make something very white that's thick." The more layers a material has, he says, the stronger it can scatter light and the brighter its color can be. In this week's Science Vukusic and his colleagues report that the bug's five-micrometer-thick scales were whiter than a child's baby tooth, which is encased in a millimeter-thick layer of white enamel. They used an international standard to assess the beetle's relative whiteness. Electron microscopy revealed the scales are made of a tangle of seemingly randomly oriented filaments, each about 250 nanometers wide. A random microscopic structure is key to producing a white color, which results when all wavelengths of light scatter equally from a surface. If the surface contains any repeating pattern, it will reflect light of the wavelengths that match that pattern.

Image: COURTESY OF PETE VUKUSIC/EXETER UNIVERSITY WHITE STANDS OUT: White coloring is unusual in nature because it requires a surface to reflect all wavelengths of light strongly. To confirm the randomness of the filaments, the researchers took a cross-section image of the filament network and performed a mathematical technique called a Fourier transform, which reveals any repetition in a shape. They also shined a laser beam through one of the scales and projected the resulting pattern onto a curved surface. Any repetition in the scale's internal structure would show up in the pattern of projected light. Neither technique turned up any signs of nonrandomness, the group reports. Vukusic says the brightness of the color results from gaps of air between the filaments. Light scatters every time it passes between two materials that differ greatly in the speed of light through them, also called their refractive index. Like facets in a diamond, the more places light can scatter, the brighter the ultimate color. "If you separate the scattering centers, but not by too much, then you actually improve the efficiency at which the whole light spectrum is scattered," Vukusic says. If manufacturers can learn how to harness this effect, he says, they might be able to whiten just about anything that's white.

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The Incredible, Medical Egg

Genetically modified chickens that produce medicines in their eggs may be the drug factories of the future

By David Biello

Image: COURTESY OF ROSLIN INSTITUTE CHICKEN OR THE EGG: A genetically modified rooster has produced a flock of hens that make medicines inside the whites of their eggs. The chicken egg has a storied history in medicine. Even today, millions of ordinary fertilized eggs are each punctured with a drill and injected with flu virus to make vaccines. Now, scientists at the same research institute that cloned Dolly the sheep have produced a genetically modified rooster whose female descendants lay eggs that produce medicines in place of a protein in egg whites. Helen Sang of the Roslin Institute in Edinburgh, Scotland, and her colleagues used lentivirus to introduce a gene into freshly fertilized chicken embryos that trigger the production of various drugs rather than the protein ovalbumin, which normally makes up roughly 54 percent of egg whites. The researchers screened the resultant cockerels for one that produced the new gene in its semen. They then bred him with normal hens to produce a flock of chickens that carried the inserted gene thereby producing medicines in their egg's whites.

Tests of the flocks' eggs showed that they could produce either miR24--a monoclonal antibody used in treating melanoma--or interferon b-1a--an immune system protein used against multiple sclerosis, among other things--depending on which gene was inserted. The chickens produce 15 to 50 micrograms per milliliter of egg white, the researchers found, and though this is not as efficient as the expression of ovalbumin, it is efficient enough to allow for subsequent purification into therapeutic drugs. "We would expect the transgene not to be as efficient as the endogenous gene it was based on as only some of the regulatory elements were used and the transgene may be inserted in the chromosome at a position that does not favor anywhere near maximal expression," notes Roslin's Adrian Sherman, who also participated in the research. "I'm sure there is potential for improvement."

Chicken eggs may prove a better way to producepharmaceuticals than other genetically modified products (such as goat milk) that have been previously explored. Chickens are easy to raise, produce numerous eggs, and are cheap to keep. And, after raising five generations of the modified birds, the researchers have observed no adverse health effects, according to the paper published online January 15 in Proceedings of the National Academy of Sciences USA. Even though the therapeutic proteins worked as intended during in vitro assays, it will be years before the process is ready to be used to produce drugs for human consumption, researchers say. Roslin's chickens join a similar effort using stem cells developed by Origen Therapeutics. Regardless of which "biofactory" delivers drugs first, a new medicinal use for the venerable egg is now apparent.

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Special Report: 10 Promising Treatments for World's Biggest Health Threats

Cutting-edge pharmaceuticals now being tested could revolutionize the fight against cancer, Alzheimer's, HIV, diabetes, nicotine addiction and other devastating diseases

By Charles Q. Choi

Image: © Matthias Kulka/zefa/Corbis Treatments for diabetes, smoking, Alzheimer's disease and lung cancer are just a few of the potentially lifesaving cures Scientific American has chosen to highlight in this year's roundup of drugs you've never heard of, despite their potentially huge impact on global health. These 10 treatments, all of which could significantly impact global health and wellness, are currently running the last gauntlet a pharmaceutical must run before it becomes available to the public--the clinical trial. During this trial researchers test the drug on humans, carefully observing its side effects as well as its overall effectiveness.

All of the following substances have already passed phase I safety trials and are proceeding into phase II or III efficacy and toxicity trials. (One caveat: any therapy in development runs a risk of failure, even after passing phase III.) A number of these trials represent completely novel classes of therapy, such as employing fragments of RNA that interfere with problem genes or developing vaccines meant to quell drug addiction. Some of this year's candidates target the usual rogues' gallery of killers, such as malaria, lung cancer and HIV. Many of the disorders targeted by the following treatments are becoming increasingly widespread. These disorders include diabetes, which the Centers for Disease Control and Prevention projects will someday afflict one in three children born today; Alzheimer's, which has become more common as life expectancy has increased; and the dengue viruses, which are causing larger and more frequent epidemics, especially in the tropics. One of this year's drugs even has the potential to serve as a safer replacement for the painkiller Vioxx. Alzheimer's Disease--Alzhemed A new drug targeting the root of this debilitating degenerative disease could be the vanguard of a novel class of treatments Dengue--Live attenuated 17D yellow fever and dengue chimera

A disease afflicting half a million people annually requires a special kind of vaccine Diabetes--Technosphere Insulin System Inhalable insulin could help diabetics regulate blood sugar to an unprecedented degree Hepatitis C--E1E2/MF59 The world's first preventative vaccine against Hepatitis C could curb the spread of the disease that killed Allen Ginsberg and thousands of others Arthritis--Naproxcinod Potential replacement for Vioxx combines the powers of nitroglycerin with those of nonsteroidal anti-inflammatory drugs Lung Cancer--Stimuvax New vaccine against the deadliest of all cancers teaches the body to defend itself while avoiding the side effects of more traditional therapies Malaria--RTS,S/AS02A Killing more than two million people, mostly children, every year, this disease will finally face the first ever commercially available vaccine designed to fight it Smoking--NicVAX Immunizing the body against nicotine might be just what smokers need to quit for good Vision Loss--Bevasiranib First a Nobel Prize, and now a potentially viable treatment: the world's first interfering RNA drug could be the first of many HIV--HPTN 046 and Nevirapine Preventing the half-million cases of mother to child transmission of HIV every year would go a long way to turning the tide of an epidemic.