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Our Universe in glorious detail
A revolutionary probe sittingfar out in space has revealed the bestpicture yet of theearlyUniverse-StephenBattersbyruns through the key statistics WIE NOW have a clear view of the cosmos. This week, the first results from the Microwave Anisotropy Probe were announced, giving us a clearer picture than ever before of what the Universe is like. From MAP's chart of the early Universe, Charles Bennett at NASA's Goddard Space Flight Center in Maryland and his team have extracted the essential properties of the cosmos. Instead of fuzzy estimates we now know accurately the Universe's age, rate of expansion and the proportions of its main ingredients. "We now have a standard model of cosmology," says [email protected] Spergel, of Princeton University. MAP has also provided strong evidence that the big bang got its kick from a process called inflation. Since its launch in June 2001, MAP has been measuring what's known as the cosmic microwave background. This faint radiation comes from all directions and dates from when the Universe was just 380,000 years old, when the matter that filled space had cooled enough to become transparent. The afterglow has been cooling ever since due to the Universe's expansion, and its temperature now averages a chilly 2.735 kelvin. Measuring its subtle variations gives us a picture of the infant Universe, frozen in time. MAP's predecessor COBE made headlines worldwide when it first detected the faint ripples in the microwave background in 1992. MAP has now built up a much more detailed picture of that radiation, charting fluctuations in temperature as small as a few millionths of a degree (see above). The regions of hotter and cooler radiation on this image reflect variations in the density of primordial matter. The denser patches are the seeds of galaxies and other structures in our modem Universe, and hidden in the pattern are the vital statistics of the cosmos. The largest blobs, stretching across several degrees of the sky, are typically about 25 millionths of a degree warmer or cooler than the average. But as you zoom in to smaller scales, the pattern gets more interesting. The strength of the variations changes with the scale, peaking and falling several times as you zoom in. These "acoustic peaks" hold the most important cosmological clues, as the size and strength of the peaks depend on the physical characteristics of the Universe. For example, dark matter and ordinary matter have different mechanical properties, so the cosmic ratio of the two affects how easily primordial blobs of a given size form or collapse, changing the patterns in the radiation. The position of the peaks also reveals the overall geometry of space, because if sp*ice were curved it would act like a lens, magnifying or reducing the apparent size of particular blobs. The blobs don't seem to be magnified or reduced, so space must be flat. Different cosmological parameters have overlapping effects on the background radiation, but the team has teased them apart by modelling every imaginable combination. "We generate tens of thousands of different cosmological models - our book of suspects - and compare them with what we see in the data," says Bennett. And at last, after decades of uncertainty, . we have some precise numbers. The Universe according to MAP is 13.7 billion years old - almost exactly three times the age of the Earth. And we now know its expansion rate: each megaparsec- long stretch of space is getting longer at 7i kilometres per second (a parsec is 3.26 light years). just four per cent of the Universe is ordinary matter, the stuff of stars and planets, while 23 per cent is dark matter, particles that don't emit any visible radiation. And 73 per cent is dark enery, which appears to be accelerating the expansion of space.
Lamps lit early in cosmic history
THE Universe lit up just 200 million years after it was born, according to evidence gathered by MAP. That's a surprise fbr astrophysicists, who had thought that the cosmos was pitch black fbr half a billion years. The darkness began when the fires of the big bang subsided and the Universe was tiled with cool pses that emitted little radiation. Until now, no one knew when the dark age ended because arrj light reaching us now ftm the earliest objects would be too faint fbr our telescopes to detect. MAP has not seen this first light, but a subtle side effect.
The probe has found that the microwave backgmund radiation is slightly polarised. This polarisation happened when microwaves scattered off free electrons. So something must have been pumping out ultraviolet radiation - enough to ionise hydmgen gas and release its electmns. on small scales, the polarisation is blurred. That's because micmwaves ftm nearby points in the sky can travel to the same point and then scatter in our direction, so they overlap. But on larger scales, patches of sky bigger than 200 million light years across, MAP researchers saw a strong polarisation signal. That means that microwaves ftm such distant points had not had time to travel far enough to overlap with each other when they were scattered. Since micmwaves travel at light speed, the Universe must have been just 200 million years old when poladsation happened, the team condudes. So what created the Un@'s first light? ft was probably a generation of giant stars. According to recent computer models, these would have been up to a few hundred times the mass of the Sun, and mariy millions of times brighter. But the same models predict that they shouldn't have started to form fbr at least hatf a billion years after the big bang. So MAP may be telling us that the physics in these models is wrong. Or maybe the light didn't come from stars at all. Massive black holes born in the big bang or shortly afterwards may have begun to consumethe gas around them, turning into brilliant sources of radiation.
RNA INTERFERENCE Disease genes can be silenced PHILIP COHEN
FOR the first time, an ancient form of cellular self-defence has been exploited to protect living animals against disease. If this "RNA interference" technique can be made to work in people too, it could one day be used to treat everything from cancer to HIV. RNA interference (RNAI) exploits an ancient part of the immune system that protects plants and animals against invaders by shutting off their genes. It involves designing tiny RNA molecules that match part of the sequence of the messenger RNA copy of any target gene. These small interfering RNAs (siRNAs) switch on the host's defence system, blocking production of the protein that the gene codes for (see New Scientist, 14 September 2002, P 32). Geneticists studying plants and worms have exploited RNAI for some time. But the recent discovery of a similar system in mammalian cells has created much excitement, as it could be a powerful way to snuff out genes that trigger disease. Last year a flurry of studies showed that RNAI could be used to stop viruses replicating in human cells grown in the lab, and even shut down genes in mice. But that didn't prove the technology was effective enough to treat disease. Work by Judy Lieberman's team at Harvard Medical School in Boston now shows it can be. The researchers succeeded in protecting mice against liver disease using RNAI. Their target was the gene coding for a protein called Fas, a receptor that sits on the surface of cells and triggers cell death when activated. Fas normally helps protect the body against cancer, but it can also be switched on by viruses, a malfunctioning immune system or chronic alcoholism, leading to a variety of liver diseases. "The liver has a lot of Fas, so it is very sensitive to this death receptor," says Lieberman. Lieberman's team simply injected the anti-Fas siRNAs into the tails of mice. Nearly go per cent of liver cells took up the molecules, and the number of the Fas receptors on these cells fell dramatically, to almost undetectable levels.
"I wouldn't have expected to see thatgood an effect in an organ, given the crude method of delivery"
Then, to mimic severe hepatitis, the researchers injected mice with antibodies that bind to Fas and trigger the cell suicide programme. While 4o normal mice all died within three days, 33 Out Of 40 mice that had been injected with siRNAs survived for 10 days. At that point the animals were killed so the team could examine their livers. The organs appeared completely normal (Nature Medicine, DOI: 10-1038/nm828). "That's pretty amazing considering this paper represents our first attempt," says Lieberman. "We haven't optimised it at all.' Gregory Hannon, an RNAI researcher at Cold Spring Harbor Laboratory in New York State, agrees. "I wouldn't have expected to see that good an effect in an organ, given the crude method of delivery," he says. "It's quite a nice demonstration of how this might work as a therapeutic." However, because people are so much larger than mice, simply injecting them with siRNAs probably will not work. But several groups are already working on ways to target siRNAs to specific organs. 0
Is gravity leaking away.?
DARK energy, the elusive force that seems to be pulling the Universe apart, may not exist after all. Two physicists say that rather than being caused by an extra force, the Universe's speeding expansion could be explained by gravity leaking out into a huge extra dimension, weakening its effect over long distances. Astronomers originally thought that since the early moments after the big bang, the rate of the Universe's expansion must have been falling. But in i998, they found that the light from distant supernovae was dimmer than expected, implying that space is accelerating outwards. The flndings proved to be a headache for physicists, who have been struggling ever since to explain what force could be counteracting gravity and pushing the matter in the Universe apart. One altemative explanation to dark energy might be that gravity is somehow weaker than expected over long distances. But until recently no one had been able to say how or why this might happen. Gia Dvali and colleagues of New York University say they have an answer - gravity is leaking out into extra dimensions. Small extra dimensions wouldn't do the job, as they would only affect gravity over very short distances. To affect gravity over such huge scales, the extra dimensions would have to be infinite in volume. So the NYU group started looking at a class of theories called "brane-world" scenarios, which see the Universe as a membrane floating on one or more extra, infinite dimensions of space. Now Dvali and and Michael Turner of the University of Chicago in Illinois have taken Einstein's equations of gravity, which tell us how the expansion rate of the Universe depends on the density of matter and energy within it, and tweaked them to account for the effects of these extra dimensions. When they ran the equations for just one extra dimension, they found that the Universe the equations predicted accelerates just like our own (www.arxiv.org/abs/astro- ph /0301510; wwwarxivorg/ abs/hep-ph/0212o6g). "in our approach there is no dark energy, the effect of dark energy is completely imitated by gravity itself," explains Dvali- Although the brane-world scenario might seem far-fetched, the cause of the acceleration is likely to be something very exotic, says Tumer, so it's important to get different ideas on the table. "We need to think outside the box. This is thinking outside the Universe," he says. Other experts are also open to the idea. "We have no idea what's going on at this point, so it's definitely worth exploring the possibilities," says Harvard University's Lisa Randall, who specialises in theories that involve extra dimensions. A proposed satellite caned the SuperNova/Acceleration Probe (SNAP), which could launch as soon aS 2009, will make more detailed observations of distant supemovae that could test the theory, says Dvali. Extremely sensitive laser measurements of the Earth-Moon distance might also be able detect whether the effects of gravity are modified in the way that Dvali and Turner predict. J. R. Minkel
Going the way of the dodo?
In a bid to save the rhino, conservationists suggested using saiga horn instead of rhino horn in traditional medicines. Their plan has backfired as hunters run amok FRED PEARCE
AN ANTELOPE that just a decade ago crammed the steppes of central Asia is this spring on the verge of extinction, victim of an epidemic of poaching. Biologists say it is the most sudden and dramatic population crash of a large mammal ever seen. In 1993, over a million saiga antelopes roamed the steppes of Russia and Kazakhstan. Today, fewer than 3o,ooo remain, most of them females. So many males have been shot for their horns, which are exported to China to be used in traditional fever cures, that the antelope may not be able to recover unaided. The slaughter is embarrassing for conservationists. In the early iggos, groups such as WWF actively encouraged the saiga hunt, promoting its horn as an altemative to the horn of the endangered rhino. Saiga (Saiga tatarica) once dominated the open steppes from Ukraine to Mongolia. They have always been hunted for meat, horns and skins. However, even in Soviet times, hunters killed tens of thousands each year, without dramatically lowering the population. But since the collapse of the Soviet Union, a lucrative market in the horns has opened up, with hunters using motorcycles and high-powered weapons to chase and kill their quarry. In China, saiga horns fetch around $loo a kilogram. Organised gangs illegally export the horn by train from Moscow to Beijing, or across the border from Kazakhstan.
"The plains used to be black with these antelopes, but now you can go out there and not see any at all," says Abigail Entwistle, a zoologist from Flora and Fauna International, a British-based charity. "This is the most sudden change in fortune for a large mammal species recorded in comparison may be with the African elephant, which faced a similar poaching frenzy in the 198os, causing its numbers to fall from a million to half a million in a decade. But the saiga's numbers, which started at a similar level, have fallen by 97 per cent. The scale of the slaughter, and its almost total destruction of the male saiga, has overwhelmed the animals'famed fecundity. "We don't know of any case in biology where the sex ratio has gone so wrong that fecundity has crashed in this way," says Eleanor Milner-Gulland of Imperial College, London, the leading expert in the West on the species. Between 1993 and 1998, saiga numbers across central Asia almost halved, to around 6oo,ooo. Then, with most of the males gone, the population crash began in earnest, says Milner-Gulland. Numbers have halved each year since, until last year's census recorded just 30,000 individuals. There is, she says, no sign that the crash is due to disease or unusual weather. One of the most critically endangered herds is in the huge Betpak-Dala region in central Kazakhstan, where in 1993 more than half a million saiga lived. By last year their numbers had crashed tO just 4000 - a 99 per cent drop from which there may be no return. Aerial surveys last year by the Institute of Zoology in Kazakhstan revealed no adult or juvenile males, only females, says Milner-Gulland. And time is running out to bring extra males in, as saiga antelopes normally only live for three to four years. Conservationists have struggled to keep up with the scale of the disaster, and did not put the saiga on the Red List of critically endangered species until October 2002. In the coming months they will launch an emergency appeal to rescue wild herds. "We think we have probably got just two years to save the species," says Entwistle. "The trouble is, most people have never heard of the animal, so it is hard to raise funds." It is unlikely that hunters will drive the saiga to total extinction, as they did the dodo, quagga and passenger pigeon. But without a dramatic reversal of its fortunes, it will soon be confined to zoos and a few small reserves. A decade ago, the saiga antelope seemed so secure that conservationists fighting to save the rhino from poaching suggested using saiga horn in traditional Chinese medicines as a substitute for rhino horn. Research commissioned by WWF at the Chinese University of Hong Kong in the late ig8os found it to be as effective as rhino horn in fighting fevers, and in 1991 WWF began a campaign in Hong Kong to publicise it as an altemative. The following year, the UN Environment Programme appointed WWF ecologist Esmond Bradley Martin as its "special envoy" to persuade pharmacists across Asia to adopt saiga hom (New Scientist, 9 March 1991, P 15, and 3 October 1992, p 10). But the saiga had died out in China in the 196os, and the resulting upsurge in demand opened the floodgates to unregulated imports. By 1993, says Milner-Gulland, "Hong Kong markets were piled high with saiga horn" from Kazakhstan and Russia. The slaughter had begun. Bradley Martin is unapologetic. He told New Scientist: "I supported the use of saiga antelope horn as a substitute for rhino horn from the early 198os. In my opinion it was the correct policy at the time. But I stopped around 1995, when I read about the start of the sharp decline in saiga populations."
Britain wants genetically modified food to have DNA bar codes
THE British government Is considering fbming blotech companies to use 'IDNA bar coding" to lden" genetically modifled organisms. This week the National Institute of Agricultural Botany (NIAB) in Cambridge was granted a patent on a DNA bar-coding technique. The technology would make it easier fbr regulators to trace GM fbod or detect craps that have been contaminated by GM strains. lt could also have wider uses. Banknotes or designer clothes made from bar-coded cotton would be harder to counterreit. A spokesman fbr Bfltain's Department fbr Environment, FDod and Rural Affairs (DEFRA) says lt Is too earlyto commit to any one method, but told New Scientist that such technology would be "actively encouraged".
"A single,simple DNA test could identify any bar-coded product as genetically modified if it contains intact DNA!'
A recervt Eumpean Union directive gim governments the power to make [t compulsory. "We have been talking about techniques fbr encoding unique identifiers in the context of GMOs lbr some time," says Howard Datton, DEFRA's chief scientiflc adviser. "Any development which would help In the process cyf detecting and identifying GMOs would be welcomed." The idea is to add the same unique sequence to all GM organisms, regardless cvf how else they are modifled. That means a single, simple DNA test could Identify army product as GM if lt contains intact DNA. Since such a sequence would not code fbr ariy protein, it would not affect a plant's pmperdes. Most creatures' genomes are already littered with vast stretches of non-coding DNA. DNA bar codes could also provide detailed Information about a pmduct. NIAB's patent describes how a series of sequences that contain compressed Information - such as which odmparry made the GM organisms and what modlflcations lt has - could be added. 'Simpler techniques fbr acces to that Information vall help us ensure eftctwe traceability and labelling thmugh the food supply chain. This will ensure consumer choice and Increase confidence," says Dalton. Detecting GM products Is difficutt at pmksent, because you have to know what you are looking fbr, says Derek Matthews, a molecular biok)gist at NIAB. For example, you need to know the short sequences that flank ariy added piece of DNA, or the sequence of added genes or of the DNA regions that contmi their activity. But blotech companies are often reluctant to reveal such l.ifoi,.iation because of fears that other companies may copy their technology. For lnstance,Gro-ingunnHemreatthe - National Institute of Nutrfflon and Seafood Research In Bergen, Norway, has been trying fbr nearlythree years to get data and material ftm a number of blotech companies fbr a research project, without summ. The recent EU directive also requires blotech companies to supply detailed lm'brmation on every GM product, including hovv to identify it, before approval. But companies are still reluctant to cooperate. utt's very, very difficuft to get stuff out of them, even though they are legally obliged," says Matthews. He thinks most companies would prefer genetic bar codes, since this would allow them to label their pmducts without giving away ariy secrets. The Agricuftural Biotechnology Council, which represents the BrMsh lndus", has given the idea a cautious welcome. Over mafr .y generations, DNA bar codes could be corrupted or k)st, but lt won't matter If only a few plants in a fleld lose their bar code. And NIAB's patent includes techniques fbr error correction just like those used In computem. Duncan Graham-Rowe
Modified crops 'have big benefits for Third World'
TRIALS of genetically modifled cotton In India have produced spectacular results. But not all farmers In India have reported the same benefits. Results ftm fleld trials in 2001, which were organised by Monsanto's Indian representative Mahyco and supervised by the govemmeryt, show Monsanto's Bt cotton can reduce pesticide use by 60 per cent and Increase yields by up to 80 per cent compared with t%vo non-Bt strains (Science, vol 299, p 600). The researchers conclude that GM craps can produce even greater benefits in developing countries thanintheWest.ButBtcottoncmps have reportedly failed In parts of India. This may be because the Bt strains are ncvt as well adapted to local conditions as traditional strains. The market has also been flooded with seeds collected ftm fields. Plants grown ftm these seeds will not have the same vigour as the original hybrids. To complicate things further, unappmved stmins of Bt cotton are also being grown. "Mismanagement may cause a technology to underpertbrm," says team member David Zilberman of the University of Callfbmia, Berkeley. "What we really show Is that the potential is there.11 He admh3 that there is a danger the bollworm will develop resistance to the Bt twdn. To help avoid this, 20 per cent of flelds should consist of non-Bt "refuges". But Suman Sahal of Gene Campaign in New Delhi wams that farmers with limited land will not comply with requirements to SOt aslde such areas.