When the dog days of summer come to an end, one thing we can be sure of is that the school year that follows will see more fights over the teaching of evolution and whether intelligent design, or even Biblical accounts of creation, have a place in America’s science classrooms.

In these arguments, evolution is treated as an abstract subject that deals with the age of the earth or how fish first flopped onto land. It’s discussed as though it were an optional, quaint and largely irrelevant part of biology. And a common consequence of the arguments is that evolution gets dropped from the curriculum entirely.

This is a travesty.

It is also dangerous.

Evolution should be taught — indeed, it should be central to beginning biology classes — for at least three reasons.

First, it provides a powerful framework for investigating the world we live in. Without evolution, biology is merely a collection of disconnected facts, a set of descriptions. The astonishing variety of nature, from the tree shrew that guzzles vast quantities of alcohol every night to the lichens that grow in the Antarctic wastes, cannot be probed and understood. Add evolution — and it becomes possible to make inferences and predictions and (sometimes) to do experiments to test those predictions. All of a sudden patterns emerge everywhere, and apparently trivial details become interesting.

The second reason for teaching evolution is that the subject is immediately relevant here and now. The impact we are having on the planet is causing other organisms to evolve — and fast. And I’m not talking just about the obvious examples: widespread resistance to pesticides among insects; the evolution of drug resistance in the agents of disease, from malaria to tuberculosis; the possibility that, say, the virus that causes bird flu will evolve into a form that spreads easily from person to person. The impact we are having is much broader.

For instance, we are causing animals to evolve just by hunting them. The North Atlantic cod fishery has caused the evolution of cod that mature smaller and younger than they did 40 years ago. Fishing for grayling in Norwegian lakes has caused a similar pattern in these fish. Human trophy hunting for bighorn rams has caused the population to evolve into one of smaller-horn rams. (All of which, incidentally, is in line with evolutionary predictions.)

Conversely, hunting animals to extinction may cause evolution in their former prey species. Experiments on guppies have shown that, without predators, these fish evolve more brightly colored scales, mature later, bunch together in shoals less and lose their ability to suddenly swim away from something. Such changes can happen in fewer than five generations. If you then reintroduce some predators, the population typically goes extinct.

Thus, a failure to consider the evolution of other species may result in a failure of our efforts to preserve them. And, perhaps, to preserve ourselves from diseases, pests and food shortages. In short, evolution is far from being a remote and abstract subject. A failure to teach it may leave us unprepared for the challenges ahead.

The third reason to teach evolution is more philosophical. It concerns the development of an attitude toward evidence. In his book, “The Republican War on Science,” the journalist Chris Mooney argues persuasively that a contempt for scientific evidence — or indeed, evidence of any kind — has permeated the Bush administration’s policies, from climate change to sex education, from drilling for oil to the war in Iraq. A dismissal of evolution is an integral part of this general attitude.

Moreover, since the science classroom is where a contempt for evidence is often first encountered, it is also arguably where it first begins to be cultivated. A society where ideology is a substitute for evidence can go badly awry. (This is not to suggest that science is never distorted by the ideological left; it sometimes is, and the results are no better.)

But for me, the most important thing about studying evolution is something less tangible. It’s that the endeavor contains a profound optimism. It means that when we encounter something in nature that is complicated or mysterious, such as the flagellum of a bacteria or the light made by a firefly, we don’t have to shrug our shoulders in bewilderment.

Instead, we can ask how it got to be that way. And if at first it seems so complicated that the evolutionary steps are hard to work out, we have an invitation to imagine, to play, to experiment and explore. To my mind, this only enhances the wonder.

當(dāng)三伏天要過完時(shí)，我們能確定的一個(gè)事情就是接著要來(lái)的學(xué)期會(huì)有更多有關(guān)進(jìn)化論的教學(xué)的抗議，是否設(shè)計(jì)論或圣經(jīng)的創(chuàng)造說在美國(guó)科學(xué)課堂上會(huì)占有一席之地。

在這些爭(zhēng)議性話題中，進(jìn)化論被當(dāng)作一門抽象學(xué)科，它處理著地球的年代學(xué)或者講述魚最先是怎么樣跳上陸地的。這種討論好象是可選擇的、離奇的或與生物根本無(wú)關(guān)的事情。爭(zhēng)論的通常后果就是進(jìn)化論從整個(gè)課程中下降了。

這是一個(gè)歪曲。

而且也很危險(xiǎn)。

進(jìn)化論應(yīng)該教的，確實(shí)，進(jìn)化論應(yīng)該是生物課啟蒙的核心。這樣說基于下面三個(gè)原因。

其一，它朝代了有力的框架研究我們所生活的世界。沒有進(jìn)化，生物就只是一堆互不關(guān)聯(lián)的事實(shí)，一套描述而已。讓人吃驚的各種特性，從每晚狂飲酒的樹鼩寶寶到長(zhǎng)在南極荒場(chǎng)上的青苔，都不能得到調(diào)查和理解。加入進(jìn)化論，才可以進(jìn)行推論和預(yù)測(cè)，并且有時(shí)候可以做實(shí)驗(yàn)來(lái)驗(yàn)證這些預(yù)測(cè)。忽然間，花樣到處出現(xiàn)，并且很明顯，瑣碎的細(xì)節(jié)也開始變得有趣。

進(jìn)行進(jìn)化論教學(xué)的第二個(gè)理由是這門課是此時(shí)此地就直接相關(guān)。我們對(duì)地球的影響使得其它生物體很快進(jìn)化。而且我不僅僅是在談?wù)撃切┖苊黠@的例子：昆蟲對(duì)農(nóng)藥的廣泛抵抗力，疾病抗體搞藥性進(jìn)化，從瘧疾到肺結(jié)核；比如病毒導(dǎo)致禽流感的可能也進(jìn)化成從人與人的傳播方式。我們?nèi)思宜�具有的影響還要寬泛得 。

例如，我們打獵也可以使得動(dòng)物進(jìn)化。北大西洋鱈漁業(yè)導(dǎo)致鱈魚的進(jìn)化，使鱈魚比40多年前成熟得更小更早。在挪威捕河鱒也導(dǎo)致這種魚類也帶來(lái)同樣的變化。人類對(duì)大角綿羊戰(zhàn)利性狩獵使這種大角綿羊進(jìn)化為一種小角羊。以上種種又偶然地與進(jìn)化預(yù)測(cè)相吻合。

相反，捕殺瀕臨滅絕的動(dòng)物也會(huì)導(dǎo)致其原有被捕殺者物種的進(jìn)化。有關(guān)孔雀魚的實(shí)驗(yàn)就證明，沒有捕食者以后，這些魚進(jìn)化的色彩更明亮，成熟得晚，較少扎堆在淺灘上，同時(shí)也失去了很快從某物上突然游走的能力。這種變化可以發(fā)生在5代以內(nèi)。如果你接著又引入一些捕食者，魚就會(huì)變得越來(lái)越少。

這樣，沒有考慮其它物種的進(jìn)化也可能導(dǎo)致對(duì)物種保護(hù)不成功。同樣，要保護(hù)我們自己免受疾病、害蟲和食物短缺的傷害。總之，進(jìn)化論并不是很遠(yuǎn)的抽象的學(xué)科。不能很好地教授這門學(xué)科可能會(huì)讓我們對(duì)未來(lái)的挑戰(zhàn)準(zhǔn)備不足。

教進(jìn)化論的第三個(gè)原因就更哲學(xué)一點(diǎn)。它考慮到對(duì)待證據(jù)的態(tài)度發(fā)展。“有關(guān)科學(xué)的共和戰(zhàn)”，記者Chris Mooney雄辯地爭(zhēng)論說，藐視科學(xué)證據(jù)，或任何形式的證據(jù)，充滿在布什政府的政策中，從氣候變化到性教育，從石油開采到伊拉克戰(zhàn)爭(zhēng)。對(duì)進(jìn)化的不屑一顧是其普遍態(tài)度的主要原因。

此外，由于科學(xué)課堂本身就最先蔑視證據(jù)，因此也有爭(zhēng)議說它是第一個(gè)需要培養(yǎng)的地方。一個(gè)意識(shí)形態(tài)不講究證據(jù)的社會(huì)可能會(huì)出大亂子。這并不是說科學(xué)永遠(yuǎn)不會(huì)被左派意識(shí)曲解，如果有時(shí)候會(huì)這樣，結(jié)果并不會(huì)更好。

但對(duì)于我來(lái)說，研究進(jìn)化論的最重要的事情是一些更無(wú)形的事情。這就是說，一些努力包括深?yuàn)W的樂觀主義。這意味著，當(dāng)我們遇到一些本質(zhì)上復(fù)雜神秘的事情時(shí)，如細(xì)菌的鞭毛或螢火蟲發(fā)現(xiàn)的光時(shí)，我們并不需要尷尬地聳肩。

相反，我們可以問問怎么會(huì)這樣。如果最初看止去很復(fù)雜以至于很難理解進(jìn)化的步驟，我們歡迎大家來(lái)想象、游戲、實(shí)驗(yàn)和探究。照我的看法，這只會(huì)增強(qiáng)好奇。