第1段

Polar bears are being increasingly threatened by the effects of climate change, but their disappearance could have far-reaching consequences. They are uniquely adapted to the extreme conditions of the Arctic Circle, where temperatures can reach-40°C. One reason for this is that they have up to 11 centimetres of fat underneath their skin. Humans with comparative levels of adipose tissue would be considered obese and would be likely to suffer from diabetes and heart disease. Yet the polar bear experiences no such consequences.

第2段

A 2014 study by Shi Ping Liu and colleagues sheds light on this mystery. They compared the genetic structure of polar bears with that of their closest relatives from a warmer climate, the brown bears. This allowed them to determine the genes that have allowed polar bears to survive in one of the toughest environments on Earth. Liu and his colleagues found the polar bears had a gene known as APoB, which reduces levels of low-density lipoproteins (LDLs) – a form of ‘bad’ cholesterol. In humans, mutations of this gene are associated with increased risk of heart disease. Polar bears may therefore be an important study model to understand heart disease in humans.

第3段

The genome of the polar bear may also provide the solution for another condition, one that particularly affects our older generation: osteoporosis. This is a disease where bones show reduced density, usually caused by insufficient exercise, reduced calcium intake or food starvation. Bone tissue is constantly being remodelled, meaning that bone is added or removed, depending on nutrient availability and the stress that the bone is under.  Female polar bears, however, undergo extreme conditions during every pregnancy. Once autumn comes around, these females will dig maternity dens in the snow and will remain there throughout the winter, both before and after the birth of their cubs. This process results in about six months of fasting, where the female bears have to keep themselves and their cubs alive, depleting their own calcium and calorie reserves. Despite this, their bones remain strong and dense.

第4段

Physiologists Alanda Lennox and Allen Goodship found an explanation for this paradox in 2008. They discovered that pregnant bears were able to increase the density of their bones before they started to build their dens. In addition, six months later, when they finally emerged from the den with their cubs, there was no evidence of significant loss of bone density. Hibernating brown bears do not have this capacity and must therefore resort to major bone reformation in the following spring. If the mechanism of bone remodelling in polar bears can be understood, many bedridden humans, and even astronauts, could potentially benefit.

第5段

The medical benefits of the polar bear for humanity certainly have their importance in our conservation efforts, but these should not be the only factors taken into consideration. We tend to want to protect animals we think are intelligent and possess emotions, such as elephants and primates. Bears, on the other hand, seem to be perceived as stupid and in many cases violent. And yet anecdotal evidence from the field challenges those assumptions, suggesting for example that polar bears have good problem-solving abilities. A male bear called GoGo in Tennoji Zoo, Osaka, has even been observed making use of a tool to manipulate his environment. The bear used a tree branch on multiple occasions to dislodge a piece of meat hung out of his reach. Problem-solving ability has also been witnessed in wild polar bears, although not as obviously as with GoGo. A calculated move by a male bear involved running and jumping onto barrels in an attempt to get to a photographer standing on a platform four metres high.

第6段

In other studies, such as one by Alison Ames in 2008, polar bears showed deliberate and focussed manipulation. For example, Ames observed bears putting objects in piles and then knocking them over in what appeared to be a game. The study demonstrates that bears are capable of agile and thought-out behaviours. These examples suggest bears have greater creativity and problem-solving abilities than previously thought.

第7段

As for emotions, while the evidence is once again anecdotal, many bears have been seen to hit out at ice and snow – seemingly out of frustration – when they have just missed out on a kill. Moreover, polar bears can form unusual relationships with other species, including playing with the dogs used to pull sleds in the Arctic. Remarkably, one hand-raised polar bear called Agee has formed a close relationship with her owner Mark Dumas to the point where they even swim together. This is even more astonishing since polar bears are known to actively hunt humans in the wild.

第8段

If climate change were to lead to their extinction, this would mean not only the loss of potential breakthroughs in human medicine, but more importantly, the disappearance of an intelligent, majestic animal.

北极熊正日益受到气候变化的威胁，但它们的消失可能带来深远的后果。它们独特地适应了北极圈的极端环境，那里的温度可以达到零下40摄氏度。其中一个原因是它们皮肤下有多达11厘米的脂肪。如果人类具有相似水平的脂肪组织，将被视为肥胖，并可能患有糖尿病和心脏病。然而，北极熊没有遭受这样的后果。

2014年，刘世平等人的一项研究揭示了这个谜团。他们将北极熊的基因结构与生活在更温暖气候下的它们最近的亲属棕熊进行了比较。这使他们能够确定哪些基因使北极熊能够在地球上最艰苦的环境之一中生存下来。刘和他的同事发现北极熊有一个称为APoB的基因，它降低了低密度脂蛋白（LDL）-一种“坏”胆固醇的形式的水平。在人类中，该基因的突变与心脏病风险增加有关。因此，北极熊可能是研究人类心脏病的重要模型。

北极熊的基因组也可能为另一种特别影响我们老一代的疾病提供解决方案：骨质疏松症。这是一种骨骼密度降低的疾病，通常由于运动不足、钙摄入不足或食物匮乏所致。骨组织不断重塑，这意味着骨骼会根据营养物的可用性和骨骼所承受的压力而增加或减少。然而，雌性北极熊在每一次孕育过程中都会经历极端条件。一旦秋天来临，这些雌性熊会在雪地中挖掘产房洞穴，并在整个冬季中都待在那里，无论是在幼崽出生前还是后。这个过程导致了大约六个月的禁食，这期间雌性熊必须使自己和幼崽保持活着，消耗自己的钙和卡路里储备。尽管如此，它们的骨骼仍然保持坚固和密实。

生理学家Alanda Lennox和Allen Goodship于2008年找到了这个悖论的解释。他们发现怀孕的熊在开始筑巢之前能够增加骨骼密度。此外，六个月后，当它们最终带着幼崽离开巢穴时，没有证据显示骨骼密度有显著下降。冬眠的棕熊没有这种能力，因此在随后的春季必须进行大规模的骨骼重塑。如果能够理解北极熊的骨骼重塑机制，许多卧床不起的人类，甚至宇航员，都有可能从中受益。

北极熊对人类的医学益处在我们的保护努力中无疑具有重要意义，但这些不应是唯一需要考虑的因素。我们倾向于保护我们认为聪明并具有情感的动物，如大象和灵长类动物。然而，熊似乎被认为是愚蠢和暴力的。然而，从实地证据来看，这些假设受到了挑战，例如北极熊具有良好的解决问题能力。大阪天王寺动物园的一只叫做GoGo的雄性熊甚至被观察到利用工具来改变自己的环境。熊多次使用一根树枝将悬在它无法触及的地方的一块肉挪开。野生北极熊也表现出解决问题的能力，尽管不像GoGo那样明显。一只雄性熊精心策划了一次行动，跑过去跳上桶子，试图接近一个站在四米高平台上的摄影师。

在其他研究中，例如2008年的艾莉森·艾姆斯的一项研究中，北极熊展示了有意识和专注的操作。例如，艾姆斯观察到熊将物体堆放在一起，然后将它们推倒，看起来像是一场游戏。这项研究表明，熊具有敏捷和经过思考的行为能力。这些例子表明，熊比以前认为的更具创造力和解决问题的能力。

至于情感，虽然证据再次是凭经验的，但许多熊被看到在错过猎物时击打冰雪，似乎出于沮丧。此外，北极熊可以与其他物种形成不寻常的关系，包括与用于拉雪橇的狗玩耍。令人惊讶的是，一只名叫阿吉（Agee）的人工喂养的北极熊与主人马克·杜马斯（Mark Dumas）建立了密切的关系，甚至一起游泳。这更令人惊讶，因为北极熊在野外活动中以主动猎杀人类而闻名。

如果气候变化导致北极熊灭绝，这不仅意味着人类医学的潜在突破的损失，更重要的是，这将意味着一个聪明、威严的动物的消失。