Why should we care about nature? Should we care about it for its own sake - or for our sake, because it happens to make us happy or healthy? These might not seem like the brightest questions. Few people need convincing that the destruction of rain forests, the mass extinction of species and the melting of the ice sheets in Greenland would all be very bad things. Do we really need to list the reasons?

We do. After all, in many regards our species has already kissed nature goodbye, and we are better off for it. Technology has come to be more diverse than the biosphere. In 1867, Karl Marx observed that there were 500 types of hammer made in Birmingham, England. In 1988, Donald Norman, a cognitive scientist at the University of California, San Diego, suggested that the average American encounters 20,000 different kinds of artifacts in everyday life, which would be more than the number of animals and plants that we can distinguish. And right now, there are about 1.5 million identified species on Earth - impressive, but nothing compared to the more than 7 million United States patents.

This is mostly good news. No sane person would give up antibi­otics and anesthesia, farming and the written word. Our constructed environments shield us from heat and cold and protect us from predators. We have access to food and drink and drugs that have been devised to stimulate our nervous systems in magnificent ways. We sleep in soft beds and have immediate access to virtual experiences from pornography to classical symphonies. If a family of hunter-gatherers were dropped into this life, they would think of it as a literal heaven.

Or maybe not. There is a considerable mismatch between the world in which our minds evolved and our current existence. Our species has spent almost all of its existence on the African savanna. While there is debate over the details, we know for sure that our minds were not adapted to cope with a world of billions of people. The life of a modern city dweller, surrounded by strangers, is an evolutionary novelty. Thousands of years ago, there was no television or Internet, no McDonald's, birth-control pills, Viagra, plastic surgery, alarm clocks, artificial lighting or paternity tests. Instead, there was plenty of nature. We lived surrounded by trees and water and animals and sky.

This history has left its mark on our minds. Children are irrepressible taxonomizers, placing the world of distinct individuals into categories based on their appearance, their patterns of movement and their presumed deeper natures, and some psychologists have argued that the hard-wired capacity to organize and structure the world is specially adapted to nature: we are natural-born zoologists and botanists. We may also have evolved to get pleasure from certain aspects of the natural world. About 25 years ago, the Harvard biologist E. O. Wilson popularized the "biophilia" hypothesis: the idea that our evolutionary history has blessed us with an innate affinity for living things. We thrive in the presence of nature and suffer in its absence.

Our hunger for the natural is everywhere. It is reflected in art: the philosopher Denis Dutton, in his book "The Art Instinct," suggests that popular taste in landscape painting has been shaped by preferences that evolved for the African savanna. The appeal of the natural is also reflected in where we most want to live. People like to be close to oceans, mountains and trees. Even in the most urban environments, it is reflected in real estate prices: if you want a view of the trees of Central Park, it'll cost you. Office buildings have atriums and plants; we give flowers to the sick and the beloved and return home to watch Animal Planet and the Discovery Channel. We keep pets, which are a weird combination of constructed things (cats and dogs were bred for human companionship), surrogate people and conduits to the natural world. And many of us seek to escape our manufactured environments whenever we can - to hike, camp, canoe or hunt.

Wilson emphasizes the spiritual and moral benefits of an attachment to nature, warning that we "descend farther from heaven's air if we forget how much the natural world means to us." But there are more tangible benefits as well. Many studies show that even a limited dose of nature, like a chance to look at the outside world through a window, is good for your health. Hospitalized patients heal more quickly; prisoners get sick less often. Being in the wild re­duces stress; spending time with a pet enhances the lives of everyone from autistic children to Alzheimer's patients. The author Richard Louv argues that modern children suffer from "nature-deficit disorder" because they have been shut out from the physical and psychic benefits of unstructured physical contact with the natural world.

So the preservation of the natural world should be important to us. But how important? The psycholo­gist Philip Tetlock has pointed out that many people talk about the environment as a "sacred value," protected from utilitarian trade-offs - when the Exxon Valdez spilled nearly 11 million gallons of crude oil, 80 percent of the respondents in one poll said that we should pursue greater environmental protection "regardless of cost." But he also points to the need to balance environmental concerns with social and political and personal priorities. (Few of these respondents would be willing to hand over their pensions for a more efficient cleanup of the Alaskan shoreline.) And even if we did value nature above everything else, we would still have to decide which aspects of nature we care about the most. You can see this in the debate over the creation of giant wind farms in the ocean or on hillsides. Proponents are enthusiastic about the cheap, green energy; critics worry about the loss of natural beauty and the yearly filleting of thousands of songbirds and ducks.

In the end, an indiscriminate biophilia makes little sense. Natural selection shaped the human brain to be drawn toward aspects of nature that enhance our survival and reproduction, like verdant landscapes and docile creatures. There is no payoff to getting the warm fuzzies in the presence of rats, snakes, mosquitoes, cockroaches, herpes simplex and the rabies virus. Some of the natural world is appealing, some of it is terrifying and some of it grosses us out. Modern people don't want to be dropped naked into a swamp. We want to tour Yosemite with our water bottles and G.P.S. devices. The natural world is a source of happiness and fulfillment, but only when prescribed in the right doses.

You might think that technology could provide a simulacrum of nature with all the bad parts scrubbed out. But attempts to do so have turned out to be interesting failures. There is a fortune to be made, for instance, by building a robot that children would respond to as if it were an animal. There have been many attempts, but they don't evoke anywhere near the same responses as puppies, kittens or even hamsters. They are toys, not companions. Or consider a recent study by the University of Washington psychologist Peter H. Kahn Jr. and his colleagues. They put 50-inch high-definition televisions in the windowless offices of faculty and staff members to provide a live view of a natural scene. People liked this, but in another study that measured heart-rate recovery from stress, the HDTVs were shown to be worthless, no better than staring at a blank wall. What did help with stress was giving people an actual plate-glass window looking out upon actual greenery.

All of this provides a different sort of argument for the preservation of nature. Put aside for the moment practical considerations like the need for clean air and water, and ignore as well spiritual worries about the sanctity of Mother Earth or religious claims that we are the stewards of creation. Look at it from the coldblooded standpoint of the enhancement of the happiness of our everyday lives. Real natural habitats provide significant sources of pleasure for modern humans. We intuitively grasp this, and this knowledge underlies the anxiety that we feel about nature's loss. It might be that one day we will be able to replace the experience of nature with "Star Trek" holodecks and robotic animals. But until then, this basic fact about human pleasure is an excellent argument for keeping the real thing.

Paul Bloom is a professor of psychology at Yale and the author of "Descartes' Baby." He is currently writing a book about pleasure.

为什么我们应该要关注大自然？我们关注它，是为了大自然本身呢，还是出于我们自身的理由，因为大自然恰好令我们快乐和健康？也许还有更巧妙的方式来提出这些问题。大部分的人都相信，热带雨林的破坏、物种的大量灭绝以及格陵兰冰层的融化全部都将是非常糟糕的事情。我们还真的需要举出其中的原因吗？

的确如此。毕竟，在许多方面，人类已经告别了大自然，并因此而进步。技术手段已经变得比生物圈更为多样化。1867年，卡尔马克思注意到，英格兰伯明翰出产的锤子有500种之多。1988 年，加州大学圣迭戈分校的认知科学家Donald Norman指出，普通美国人在日常生活中接触到的人工制品多达2万种，这一数字将超出我们所能分辨出的动植物种类的数量。目前，地球上存在大约150万种可识别的物种，这一数字令人印象深刻，但是与超过700万的美国专利的数量相比就不算什么了。

这些大部分都是好消息。心智正常的人是不会放弃抗生素、麻醉术、种植养殖和书面文字的。我们所建造的环境庇护我们免于严寒酷暑，保护我们免于食肉动物的侵害。我们可以获得食物、饮料和药物，设计发明它们是为了显著地刺激我们的神经系统。我们睡于高床软枕之上，并立即可享受到从色情读物到古典交响乐的虚拟体验。要是把一个游牧家族投进这样的生活当中，他们会认为这是不折不扣的天堂。

或者也许并非如此。在人类大脑进化的世界与我们目前的生存状态之间存在着非常大的不相匹配。人类几乎花掉其全部的生存时间在非洲的热带大草原上，尽管对其中的细节存有争议，但是我们确定地知道，人类的大脑还不能适应去面对一个有数十亿人的世界。周围都是陌生人的现代城市居民的生活是进化过程中出现的新事物。几千年前，没有电视和互联网，没有麦当劳，没有避孕药、伟哥、整形手术、闹钟、人工照明和亲子鉴定。有的是大量的自然物，我们的生活围绕着树木、溪流、动物和天空。

这段历史将它的印记留在了我们的大脑中。孩子们是情不自禁的分类者， 将这个世界多种多样的个体划分成类别，按照它们的外形、运动的模式和预设的更深层的特性，一些心理学家曾认为，组织并结构化这个世界的固有本能特别适应于大自然：我们是天生的动物学家和植物学家。我们也可能已经进化到可以从自然界的某些方面获得快乐。大约在25年前，哈佛大学生物学家E. O. Wilson让"人类天生热爱大自然"的假说家喻户晓：即我们进化的历史用一种内在的对万物生灵的亲近感保佑着我们的想法。有了大自然，我们就兴盛，没有大自然，我们就受苦。

我们对大自然的渴望随处可见。反映在艺术上：哲学家Denis Dutton在其著作《艺术本能》中指出，大众对风景画的喜爱是由对非洲热带大草原的经过进化的偏好所形成的。大自然的魅力还反映在我们最想要生活居住的地方，人们喜欢靠近大海、山脉和树林，甚至在最城市化的环境中，自然之魅反映到房地产的价格上：如果你想看到中央公园树林的风景，你就要为此花一大笔钱。商业建筑有中庭和植物，我们给病人和爱人送去鲜花，我们回到家里观看"动物星球"和"发现"频道。我们养宠物，这些宠物是一种奇怪的混合产物（人们喂养猫猫狗狗是为了有个伴），它们替代了人的作用，且成为人们通向自然界的管道。许多人一旦有机会就会设法逃离我们工业化的环境，去远足，去露营，去泛舟，去打猎。

Wilson强调对大自然的依附所产生的心灵上和精神上的收益，警告说，"如果我们忘记自然世界对我们的意义有多重要，我们就会消沉下去而离极乐世界的空气渐行渐远。"不过，大自然还有更多看得见的好处。许多研究证实，即便是有限量的大自然，如透过一扇窗户看到外面世界的机会，对你的健康也是有益的。住院病人康复得更快，囚犯生病较为少见。身处荒郊野外可减轻压力，与宠物共度时光可改善每个人的生活，从患自闭症的儿童到患老年痴呆症的病人。作家Richard Louv认为，现代的儿童尝受"大自然缺乏病"所带来的痛苦，因为他们被隔绝于与自然界进行的未经结构化的身体接触所带来的身心受益。

因此，保护自然世界对我们而言应该是重要的。不过，有多重要呢？心理学家Philip Tetlock已经指出，许多人谈及环境将其作为一种"神圣的价值"，环境得到保护是出于功利主义的权衡，当埃克森石油公司的Valdez号油轮泄漏了将近1100万加仑的原油时，在一次民意调查中有8成的受访者表示，我们应该"不计成本"地寻求更大程度的环境保护。不过，他还表明了平衡环境问题与社会、政治及个人优先权的需要。（这些受访者当中很少有人会愿意拿出他们的养老金用在提高阿拉斯加海岸线清理工作的效率上。）而且，即便是我们的确重视大自然超出其他的任何事物之上，我们仍将不得不决定我们最关注的是大自然的哪些方面。在对建造位于海上或山上的大型风力发电场的争论中，你能明白这一问题。支持者热衷于廉价绿色能源；而批评者担心失去了自然风光的美丽，以及每年数千只歌鸟和野鸭的身体碎片。

最后，不加区分的对大自然的热爱没有什么意义。自然选择塑造了人类的大脑被引导朝着增加我们的繁衍生息的大自然方面而发展，如青山绿水和温驯的动物。在老鼠、蛇、蚊子、蟑螂、单纯疱疹和狂犬病毒出现的时候获得幸福感是毫无益处的。部分自然界令人向往，部分令人惊恐，部分令人厌恶。现代的人类不想光着身子被扔进一片沼泽地，我们希望带着我们的水壶和GPS设备游历 Yosemite国家公园。自然界是一个快乐和满足的源泉，不过只有在按照指定的要求用以适当的剂量的时候。

你也许会认为，技术手段可以提供一个所有不好的部分均被清除掉的大自然的模拟器。可是，尝试着这么做的结果都已被证明是有趣的失败。比如说，制造一种机器人，孩子们对着它做出的反应就好像它是一只小动物。出现过许多这样的尝试，不过，它们都没有带来任何接近于对小狗小猫甚或是仓鼠的同样反应，它们只是玩具，不是伙伴。或者，看看由华盛顿大学心理学家小Peter H. Kahn及其同事所进行的一项最新的研究，他们将50英寸的高清电视机摆放在教职员工的没有窗户的办公室中，提供自然景色的现场画面。人们喜欢这种安排，但是，另一项研究测量了从压力情绪复原的过程中心率的恢复情况，结果显示高清电视机没什么用，并不比盯着空白的墙面效果更好。真正有助于减轻压力的是给人们一块可向外望到真正的绿色植被的真正的平板玻璃窗。

所有的这些给出的都是保护大自然的另类论据。暂时撇开像需要清洁空气和水源这样的实际考虑不谈，也不去理会有关神圣地球母亲的心灵上的担忧或者人类看管万物生灵这一宗教主张。让我们从提升人类日常生活的快乐这个不带感情色彩的角度来看待保护大自然的问题。真实的自然环境给现代人类带来了重要的快乐之源。直觉上，我们完全理解这一点，我们对大自然的破坏所感受到的焦虑正是基于这种认识。也许有一天，我们将能够用电影《星际迷航》中的全息甲板和动物机器人来替代对大自然的体验，不过就算到了那时，关于人类快乐的这个基本事实仍是我们保护真实的自然世界的一个极佳的理由。

Paul Bloom是耶鲁大学的心理学教授，著有《笛卡尔的孩子》一书。他目前正在写作一本有关快乐的书。
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