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.

當三伏天要過完時，我們能確定的一個事情就是接著要來的學期會有更多有關進化論的教學的抗議，是否設計論或圣經的創造說在美國科學課堂上會占有一席之地。

在這些爭議性話題中，進化論被當作一門抽象學科，它處理著地球的年代學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關的事情。爭論的通常后果就是進化論從整個課程中下降了。

這是一個歪曲。

而且也很危險。

進化論應該教的，確實，進化論應該是生物課啟蒙的核心。這樣說基于下面三個原因。

其一，它朝代了有力的框架研究我們所生活的世界。沒有進化，生物就只是一堆互不關聯的事實，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在南極荒場上的青苔，都不能得到調查和理解。加入進化論，才可以進行推論和預測，并且有時候可以做實驗來驗證這些預測。忽然間，花樣到處出現，并且很明顯，瑣碎的細節也開始變得有趣。

進行進化論教學的第二個理由是這門課是此時此地就直接相關。我們對地球的影響使得其它生物體很快進化。而且我不僅僅是在談論那些很明顯的例子：昆蟲對農藥的廣泛抵抗力，疾病抗體搞藥性進化，從瘧疾到肺結核；比如病毒導致禽流感的可能也進化成從人與人的傳播方式。我們人家所具有的影響還要寬泛得 。

例如，我們打獵也可以使得動物進化。北大西洋鱈漁業導致鱈魚的進化，使鱈魚比40多年前成熟得更小更早。在挪威捕河鱒也導致這種魚類也帶來同樣的變化。人類對大角綿羊戰利性狩獵使這種大角綿羊進化為一種小角羊。以上種種又偶然地與進化預測相吻合。

相反，捕殺瀕臨滅絕的動物也會導致其原有被捕殺者物種的進化。有關孔雀魚的實驗就證明，沒有捕食者以后，這些魚進化的色彩更明亮，成熟得晚，較少扎堆在淺灘上，同時也失去了很快從某物上突然游走的能力。這種變化可以發生在5代以內。如果你接著又引入一些捕食者，魚就會變得越來越少。

這樣，沒有考慮其它物種的進化也可能導致對物種保護不成功。同樣，要保護我們自己免受疾病、害蟲和食物短缺的傷害。總之，進化論并不是很遠的抽象的學科。不能很好地教授這門學科可能會讓我們對未來的挑戰準備不足。

教進化論的第三個原因就更哲學一點。它考慮到對待證據的態度發展。“有關科學的共和戰”，記者Chris Mooney雄辯地爭論說，藐視科學證據，或任何形式的證據，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爭。對進化的不屑一顧是其普遍態度的主要原因。

此外，由于科學課堂本身就最先蔑視證據，因此也有爭議說它是第一個需要培養的地方。一個意識形態不講究證據的社會可能會出大亂子。這并不是說科學永遠不會被左派意識曲解，如果有時候會這樣，結果并不會更好。

但對于我來說，研究進化論的最重要的事情是一些更無形的事情。這就是說，一些努力包括深奧的樂觀主義。這意味著，當我們遇到一些本質上復雜神秘的事情時，如細菌的鞭毛或螢火蟲發現的光時，我們并不需要尷尬地聳肩。

相反，我們可以問問怎么會這樣。如果最初看止去很復雜以至于很難理解進化的步驟，我們歡迎大家來想象、游戲、實驗和探究。照我的看法，這只會增強好奇。