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Refugee species are feeling the heat of global warming
The facts about climate change are leaving sceptics with nowhere to go - much like the flowers, birds and amphibians abandoning old haunts to escape extinctionJAY WITHGOTR
THE evidence is in. Global warming is already having a widespread impact on the world's plants and animals, driving them closer to the poles and to higher altitudes, and altering the times of year they migrate and reproduce. Two analyses published this week, the most comprehensive so far, strengthen similar but tentative conclusions made in 2001 in a landmark report by the Intergovernmental Panel on Climate Change (IPCC). Both studies scoured scientific literature for data on thousands of plant and animal species, with strikingly similar conclusions (Nature vel 421, P 42 and P 57). Of the species showing recent changes in range or seasonal behaviour, four out of five shifted their ranges towards the poles or higher altitudes, and began mating and migrating earlier in the spring. Frogs are breeding, flowers are blooming and birds are migrating 2.3 days earlier on average each decade, and butterflies, birds and plants are moving toward the poles by 6.1 kilometres a decade. Such relatively small changes can sometimes mean extinction, say ecologists. Organisms can't move higher to escape the heat if they're already living on a mountaintop, for instance. Costa Rica's golden toad has been driven to extinction by climate change, as the cloud forests in which it lived have warmed and dried. "We've tended to assume all species are fixed in place and we can build parks around them to protect them," says Lee Hannah of Conservation International. "[But] with the level of habitat loss, dynamic species ranges mixed with static conservation strategies is a recipe for mass extinction." For example, in Europe and North America, some birds have been driven away from the plant- bound insects they eat. Species that live at higher latitudes, where warming is greatest, have felt the effects the most, says Terry Root of Stanford University, a former IPCC scientist who led one of the studies. And strikingly, many effects have switched direction over time: butterflies that moved north in the warm 1930S tO 40S moved south in the cooler 1950s to 6os, then north again with more recent warming. Both biologists and economists worked on the IPCC report, but they argued over the strength of evidence for warming's effects on wildlife. Economists tend to view only major present-day changes as important; biologists focus on the cumulative long-term consequences of minor impacts. Biologists at the IPCC demanded that the 2ool report assign the ecological results "very high confidence" - meaning "very serious" -but the economists pushed for "medium confidence". The final report compromised by stating that there was "high confidence" for a climate impact. So biologist Camille Parmesan of the University of Texas in Austin teamed up with economist Gary Yohe of Wesleyan University in Middletown, Connecticut, to blend the two approaches. In one of this week's papers they end up endorsing confidence levels as high or higher than the IPCC'S. Some economists are not convinced. The studies examine 11 only a tiny fraction of all species out there", says Richard To] of the University of Hamburg in Germany. "Besides, scientists prefer to investigate species that are likely to be affected by climate change, and journals prefer to publish papers with strong results. The sample is therefore not representative." But Thomas Lovejoy, president of the Heinz Center for Science, Economics and the Environment in Washington DC, comes to the authors'defence. "You simply can't apply that economics stuff to this," he says. "Biologists are trying to answer the question,Are you detecting responses in nature?'Of course the first responses are smaller than they will be later. And that's precisely why you want to find them."
Protato to feed lndia's poor ANDY COGHLAN
GENETICALLY modified potatoes will play a key part in an ambitious 15-year plan to combat malnutrition among India's poorest children. Anti-poverty campaigners have greeted the protato" with cautious support. The three-pronged attack on childhood mortality would aim to provide children with clean water, better food and vaccines. "Zero child mortality in underprivileged children would be the goal," says Govindaralan Padmanaban, a biochemist at the Indian Institute of Science in Bangalore. Formulated in collaboration with charities, scientists, government institutes and industry, the anti-hunger plan is under consideration by the Indian government. Meanwhile, the protein-rich GM potatoes are in the final stages of testing, prior to being submitted for approval. Padmanaban, who outlined the plan at a conference at the Royal Society in London last month, hopes Western-based environmental groups and charities will not demonise the project in the same way as they did AstraZeneca's "golden rice", a strain modified to make more vitamin A. "The requirements of developing countries are very different from those of rich countries," he says. "I think it would be morally indefensible to oppose it.' Asis Datta's team at the lawaharlal Nehru University in New Delhi added the An-L4i gene to potatoes, with the result that they make a third more protein than usual, including substantial amounts of the essential amino acids lysine and methionine.
"if you're going to use genetic modification at all, use it for this. India's problem is that we're vegetarian, but pulses and legumes are expensive"
AmAi is a gene from the amaranth plant, a crop long grown by native South Americans and now available in some Western health food stores. "The potato doesn't contain a pesticide gene," says Padmanaban. "it's a gene that improves nutrition, and it's from another plant that is already eaten. Moreover, it's not a known allergen." That might help make it acceptable in India, where local activists oppose the recent licensing of Bt cotton - which carries a gene for a bacterial pesticide - on the grounds it is "unnatural", and that it could kill beneficial insects. The idea is that the potatoes will form part of a midday meal to redress deficiencies in children's diets. A lack of lysine, for example, can affect brain development. The potato should only be adopted if it passes all safety and environmental requirements, and if the extra protein is digestible, says Suman Sahai of Gene Campaign, a Delhi-based sustainable development group opposed to the patenting of plants. However, Sahai says the team's goal is far more worthy than, say, creating crops resistant to a company's own weedkiller. "If you're going to use GM at all, use it for this," she says. "India's problem is that we're vegetarian, so pulses and legumes are the main protein source, but they're in short supply and expensive. The potato is good because it's cheap." Siddharth Deva, policy adviser for south Asia for the British- based charity Oxfam, agrees that the potato could serve a useful purpose. But he calls for the government's judgements on GM crops to be independently assessed by panels of experts, including environmentalists. "We want to ensure that introductions of GM crops don't have harmful implications," he says. The potato isn't the first protein-enriched crop. Strains of GM maize rich in lysine have already been created. It isn't necessary to resort to genetic engineering, of course: bread and wheat flour can also be enriched in protein simply by adding, say, peanut flour. But this is costlier and none of the various schemes to provide such bread to malnourished children since the 196os has survived, despite the benefits.
Farewell, man the hunter? BOB HOLMES
HUNTING skills may not after all have triggered the tremendous burst of human evolution at the beginning of the ice ages nearly 2 million years ago. instead of man the hunter, the driving force behind this evolutionary surge may have been woman the gatherer, with both mother and grandmother playing a vital role. For 40 years, anthropologists have leaned toward the notion that rich, nourishing meat - brought home by hunters and shared out - played a crucial role in human origins. This would explain why evolution selected for larger, smarter hunters with lighter jaws and teeth: precisely the changes seen as Homo erectus arose in eastem Africa. The hunter-driven scenario also included the formation of nuclear family groups, in which men hunted while women gathered plants and cared for their children, thus kicking off humans'social evolution as well.
But this picture may be wrong on several counts. To begin with, early men probably weren't bringing meat home to the family. Most evidence of hunting by early African Homo erectus comes from archaeological sites containing both animal bones and primitive stone tools. But most of these lie next to rivers, the kind of predator-filled habitat that today's Hadza hunter-gatherers in Tanzania call a "city of lions". "They're certainly not places where early humans were spending the night," says lames O'Connell, an anthropologist at the University of Utah in Salt Lake City. O'Connell is lead author of a critique of the hunting hypothesis published in the latest issue of the foumal ofhuman Evolution (vol 43, p 831). Instead, the remains probably represent temporary meal sites - perhaps a convenient patch of shade -where the group gathered around a fallen animal, O'Connell and his team suggest. Most likely, the "hunters" were not actually hunting either. Many of the bones bear both cut-marks from primitive stone tools and the tooth marks of animals. When the researchers compared these with marks on bones made in modern experiments, they found that the pattem of marks and the mix of bones were similar to those left by human scavengers (see Graphic). This suggests that early humans drove other predators away from freshly killed carcasses - a view now gaining support among palaeoanthropologists. But O'Connell's team went a step ftirther. They wanted to know what kind of a living early African Homo erectus made if in fact they were scavengers, not hunters. The Hadza people today scavenge avidly in the same way, and studies in the late 198os noted that they found an average of one carcass every two to three weeks. Based on that observation, the team estimated that early humans might have picked up a carcass every few days in the wettest areas, but in drier areas might have got as little as one a month: nowhere near enough to live on. If fathers weren't feeding their children meat most of the time,, that means mothers and, perhaps, grandmothers must have been. Older women might have proved crucial in feeding children, the researchers say, allowing the mothers to get pregnant again more quickly. Evolution would thus favour a long lifespan, which is closely linked to large body size and delayed maturity. Suddenly, all the major changes in human life history are explained by foraging, not hunting. Critics point out that even if the meat supply was not reliable enough to live on, it must have been important in evolutionary terms. Humans have been top carnivores - a highly unusual role for a primate - since at least the Stone Age. "Something special did happen with regard to caniivory," says Robert Blumenschine, a palaeoanthropologist at Rutgers University in New Brunswick, New Jersey. "The extent to which it shaped human evolution remains in question, but I would think it must have had some strong influence."
An awful lot of Earths may be out there
Two astrophysicists have decided the race to detect an Earth-like planet outside our Solar System is taking too long. So, instead of scanning the skies, they have modelled all the planetary systems known so far to work out which could be hiding habitable planets. They conclude that around a quarter of these are capable of harbouring other Earths, a much higher proportion than anyone expected. Since 1995, astronomers have unveiled dozens of planets orbiting nearby Sun-like stars. Current methods can only detect gas giants like Jupiter but life, at least in the form that we know it, can only get started on a solid surface where water can pool. A small terrestrial planet made of rock would be a more likely abode, but it could be years before we are able to detect such planets. To narrow the search, Serge Tabachnik and Kristen Menou of Princeton University in New jersey have created computer simulations of the 85 systems known in AuguSt 2002, the time of their research, to estimate which might harbour habitable planets.
"Fora smaller world to be habitable it must be far enough away from its larger cousins so that their gravitabonal pull does not seriously affect its orbit"
Although similar work has been carried out for a few individual solar systems, this study, which will appear in The Astrophysical Journal, is the first to address the entire known set. The first thing they looked for in each system was whether a small terrestrial planet could exist in a stable orbit. The gravitational tugs exerted by gas giants can force smaller planets into unstable orbits or eject them from a system altogether. So for a smaller world to be habitable, it must be far enough away from its larger cousins so that their gravitational pull does not seriously affect its orbit. The planet must also be within the "habitable zone": the region surrounding a star within which a planet can support liquid water at all times. The researchers found that around a quarter of the systems contained regions where life- friendly planets could in principle exist. This is much higher than previously thought, says Tabachnik. Extrapolated across the entire Galaxy, that makes a lot of new Earths. Greg Laughlin from the University of Califomia, Santa Cruz, has done similar calculations with a smaller number of systems, and agrees with these new results. "[They are] in line with what I would have expected," he says. But the authors warn that their results are preliminary. There could still be other gas giants, further away from the stars, that have not been detected yet, they point out. That could affect the stable regions that have been found so far. Mark A. Gadick
Human Childhood and Reproductive Success
sort of mind-reading skills that would have been vital for their survival in the ancestral environment (New Scientist, 13 April, P 34). All in all you get the picture of kids operating pretty much as miniature adults. Which has left a growing number of experts in human evolution questioning the notion that learning is the raison d'etre for our extended childhood. "Hard evidence that what we learn in childhood contributes to our fitness is conspicuous by its absence," comments anthropologist Ruth Mace of University College London, who studies the evolution of human life cycle stages. If a long childhood isn't designed to give kids time to learn, then what is it for? Anthropologist Barry Bogin of the University of Michigan-Dearborn has proposed a radical alternative. He believes it evolved for the benefit of parents. Bogin argues that early childhood - between about age three to seven in modern humans - is a new phase inserted into the life cycle of our ancestors to increase reproductive success. He points out that all other mammals continue suckling their young until their permanent molars have erupted and they can fend for themselves. This limits the number of offspring each mother can produce. Bogin's idea is that our prolonged childhood is the result of evolution favouring this new life cycle phase where infants are no longer totally dependent on their mothers, but can rely on other family members for food and help. This means mothers can become pregnant again even though they still have small children. The simple fact that humans are a highly successful species supports Bogin's idea. Despite our size, our long generation lengths and our long lives, we breed at the rate and with the success of small mammals with short lives. The typical interval between children is two and a half years, compared with five years for chimps, for example. More significantly, about twice as many human babies reach the age Of 15 than do chimp babies. What's more, the idea of kids as "dependent" is a modern concept that clouds our understanding of what it really means to be a child. In many parts of the world children contribute significantly to the household and are not really burdens. Across the globe, children typically look after their younger siblings and do household chores such as gathering firewood, weeding fields and tending livestock. And they do all this while still small and not competing much for resources such as food and household space. For parents in these cultures, childhood may be too short rather than too long. of course, for many families these days the tables have turned. Children may have evolved as "little helpers" but in the developed world, at least, they have become a drain on household energy and income.