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　　新的研究披露，与人们的普遍看法相反，大熊猫自身具备很强的生存能力。

　　大熊猫是世界知名度最高的象征之一，被用于推销从电子商品到碳酸饮料、巧克力至饼干、从甘草至香姻，更不用说全球环保事业了。不过由于生性胆小、过着隐居生活，它长期以来一直是地球上最为神秘的动物之一。例如，大熊猫为什么吃竹子？它们为什么看起来很难繁殖？为什么一个看起来适应力不强的物种能够幸存这么长的时间？

　　第一个问题可能是最难回答的：祖先曾是食肉动物的大熊猫的食物为何几乎全部是素食，尤其是营养价值很低的竹子。它得每天坐在地上花大半天吃竹子才能吸收到足够多的卡路里。不过，当你对这个问题进行客观的思考后，这些能耐寒的竹子生长速度很快、一年四季都有、分布广泛(直到人类出现为止)，这些特点事实上使竹子成为一种相当有吸引力的小吃。

　　当大熊猫在吸取竹子的营养时，它具备很好的身体条件：从腕骨发育而来的第六指能帮助它抓握竹茎和竹叶，健壮的头骨和强有力的牙齿能够使它碾碎树皮吃到里面的精华，它的消化功能由于一些非常强大的肠道微生物的密切合作关系而得到加强。肠道微生物的功能是如此地强大，日本科学家从熊猫大便中提取出了细菌，以用于处理厨房垃圾。他们因此成果而获得了2009年搞笑诺尔尔奖生物学奖。

　　Revealed: the secret world of the panda

　　New research has revealed that, contrary to popular beliefs, pandas are surprisingly well-equipped for survival。

　　The giant panda is one of the best-known symbols in the world, used to sell everything from electronic goods to fizzy drinks, chocolate to biscuits, liquorice to cigarettes – not to mention global conservation. Yet thanks to its shy and retiring nature, it has long been one of the planet’s most mysterious creatures. Why, for example, do pandas eat bamboo? Why do they appear to have such difficulty breeding? And how on earth has such a seemingly maladjusted species managed to survive for so long?

　　The first question has been perhaps the most difficult to answer: it seems bizarre that a creature whose ancestors were carnivores would turn towards an almost exclusively vegetarian diet, and in particular to a nutritional source as poor as bamboo. It has to spend more than half of every day sitting and eating just to extract enough calories。

　　When you think about it objectively, though, the prolific growth rate of these hardy plants, their year-round availability and widespread distribution (until humans appeared on the scene) actually made bamboo a pretty attractive snack。

　　And the panda goes about extracting what little nutrition there is in great style: a sixth digit fashioned from its wrist bone allows it to grasp at stems and strip off leaves; its hefty skull and strong teeth provide the means to crush through the tough bark to the goodness within; and its digestion is aided by an intimate symbiosis with some very powerful gut microbes. So effective are they that Japanese scientists were able to use bacteria extracted from panda faeces to achieve “the complete digestion of kitchen refuse” – a finding for which they rightly won the biology category in the 2009 Ig Nobel awards for improbable research。

　　Interestingly, when geneticists sequenced the panda’s entire genome in 2009, they found a messed-up gene that means they probably can’t taste flesh, which may explain why they don’t seek it out that often. But when the opportunity presents itself, pandas will happily tuck in. Researchers carrying out the first proper fieldwork in the 1980s found droppings that contained hair from a golden monkey and the hair, bones and hooves of a musk deer. The panda genome still contains all the enzymes needed for digesting meat, and these rare lapses into carnivory might be crucial in providing important trace nutrients that are absent from bamboo. They have also helped researchers, who have baited traps with goat heads and pig bones to lure and then collar their quarry。

　　The other thing everyone thinks they know about pandas is that they make lousy lovers. However, another long-term field project, run by Chinese scientists, has revealed that they are actually extremely good at reproduction。

　　Their bad reputation stems from their unusual breeding system, in which females are fertile for just one or two days a year. Yet during this important period, males and females show an extraordinary talent for finding each other, and are clearly not averse to sex when they do – so much so that females appear to get pregnant in the wild at virtually every opportunity. And even though newborn cubs weigh in at only 100g – the tiniest relative to adult body mass of any non?marsupial mammal – the youngsters mostly make it to adulthood quite happily。

　　None of this should really come as a surprise; after all, the panda’s peculiar reproductive strategy has served it well for millions of years (which is millions of years longer than modern humans have walked the Earth). But what is surprising is that the secret of this success comes down to their sense of smell. It turns out that pandas have “scent posts” dotted throughout the forest, trees that act as community bulletin boards on which passing individuals leave all sorts of messages alongside, overlapping or completely covering the others。

　　In the late 1990s, a brilliant series of experiments on captive pandas at the China Conservation and Research Centre for the Giant Panda in Wolong discovered that these calling cards reveal much about their owners, including their identity, sex, age and reproductive status and perhaps even an idea of how far away they are. It also made sense of the different postures that pandas assume to make their marks: the squat, the reverse, the leg-cock and, most intriguingly, the handstand, an exclusively male position that can leave urine sprinkled on the bark of a tree at more than a metre off the ground。

　　By presenting smells to captive pandas at different heights and measuring their reactions, the researchers found that the height at which scents are posted may reveal key information about an individual’s social rank. The higher up a tree an upside-down male can wee, the bigger and tougher he’s likely to be。

　　Realising that smell is the panda’s primary means of communication, chemists began to take a look at the molecular make-up of their secretions and excretions, and identified almost 1,000 different compounds. They found that not only do males and females boast a different chemical mix but each individual appears to have a pretty unique olfactory signature. The panda’s body turns out to be a kaleidoscope of scent patches: their black ears, for example, are heavily scented with urine, leading to the wonderful hypothesis that they act like miniature beacons, allowing these secretive smells to be caught by, and spread on, the wind。

　　Other experiments on captive pandas suggest that the haunting barks and honks they make have an incredibly complex structure, helping to communicate the sex, age and reproductive status of the caller, and carrying effectively through the animals’ densely forested world. Meanwhile, some cunning work on vision shows that the shape of an individual’s eyespots reflects its sex and probably its identity, with pandas being able to remember subtle differences in these shapes for at least a year。

　　These discoveries are especially impressive when you consider how short the history of panda science is. It was only in 1980, for example, that scientists made the first concerted effort to study the giant panda in its natural habitat – a joint project between China and the World Wildlife Fund, which only went ahead on condition that the charity paid $1 million to fund a state-of-the-art breeding facility。

　　This association between pandas and hard cash has continued ever since. During the 1980s, China sent pandas on lucrative short-term loans to foreign zoos. Today, most foreign zoos with pandas are paying up to $1 million per pair per year for the privilege, money that China uses to further the conservation of this emblematic species in the wild。

　　As China sets about developing its rural west, where the wild panda still has a hairy foothold, there are some big challenges ahead. But in spite of these, there are reasons to be upbeat. Since 1998, China has imposed a nationwide logging ban in natural forest that made it possible to expand the network of panda reserves from about 20 before the ban to more than 60 today. In 2006, Unesco acknowledged the Sichuan Giant Panda Sanctuaries as a World Heritage Site, occupying one million hectares of forest and embracing seven nature reserves, nine parks and almost 30 per cent of the world’s wild panda population。

　　The fortunes of pandas in captivity have also changed immeasurably in recent years. Thanks largely to our understanding of pandas’ sense of smell, the captive population is now increasing at an impressive rate; this year’s spate of births has taken the global total to more than 300, which is probably enough to maintain genetic fitness without the need to take another panda from the wild again。

　　It has been said that the panda is a maladapted species deserving only of extinction. But the fascinating stream of research that has emerged over the past 30 years should be allowed to speak for itself. It shows a creature that is certainly unusual in its genetics, appearance and behaviour – but also one with an impressive suite of exquisite evolutionary adaptations. It is true that human destruction of the pandas’ habitat has had a grave impact on this remarkable species. But with China completely behind the conservation of its “national treasure”， the prospects for its long-term survival are probably better than they have been at any point during the past 50 years。

　　(每日电讯报)

　　(解雨)