動物奧運會（下）

By the time All-Olympics move out to the pool for the swimming events， the humans are a despondent1) lot， desperate for a win. But it's not to be. Here， in fact， humans do worst of all. It shouldn't be surprising， given that our opposition， the barracuda2)， is a beautiful product of aquatic evolution， while we have been out of the water for 360 million years.

Key to the difference in speed between man and fish is the drag that each creature creates in the water. Roughly speaking， the more area of an animal's body that is perpendicular3) to the direction in which it is swimming， the greater the drag. Thus barracuda reduce their drag dramatically by means of their elongated4) teardrop shape， while humans create drag with their broad shoulders， heads， and arms.

Where an animal swims can also make a great difference to its drag. Barracuda， thanks to their gills5)， can swim far under the waves of the ocean's surface. Humans， dependent on air， splash their way across the top of the water， fighting waves， including those that they themselves create. A fish swims by using its entire body and tail to create waves that roll down its body and propel it forward. A human， on the other hand， mainly uses the muscles in the limbs. And while a barracuda can generate huge amounts of thrust with its wide tail， we humans generate most of our thrust with our relatively puny6) hands.

If one look at the ability to take metabolic7) cost and convert it to useful work—in this case， to produce thrust， then humans are only 5 percent efficient in water. Fish， sea lions， and dolphins， though are between 15 and 30 percent efficient in swimming.

In the end， humans get no gold in those imaginary All-Animal Olympics. Is this reason to despair? Not to biologist Steven Vogel of Duke University. On the contrary， he thinks there's something fitting in this. \"We can't beat the pros，\" he says， \"but on the other hand， other animals don't have a single species that could enter every Olympic event. We can swim， climb trees， and run， but we can't do them as well as the specialists. What we are is multifaceted. We've been designed for terrific behavioral versatility8).\"

當動物奧運會進展到在水池中舉行的游泳比賽時，人類已飽嘗失望，急需一場勝利?？上屡c愿違。實際上，人類在這兒的表現最差。這結果并不出人意料，因為我們的對手梭子魚是水中生物進化的完美產物，而我們已經離開海洋3.6億年了。

人和魚類在游動速度上之所以存在差別，關鍵在于每種生物在水中所產生的阻力不同。粗略地說，在與游動方向垂直的平面上，動物的身體面積越大，所受到的水的阻力也越大。因此，梭子魚依靠它們淚滴般的細長體型使阻力大大降低，而人類的寬肩、頭部和雙臂卻都會產生阻力。

動物在水中游動時所處的位置也極大地影響著產生的阻力的大小。梭子魚得益于它的魚鰓，可以在遠離海面風浪的深水中游動。而人類由于離不開空氣，只能在水面上撲騰著前進，對抗風浪以及自己的動作所引起的波浪。魚類游動時擺動全身和尾部以生成水波，水波從它身下滑過，給它向前的推力；而人類卻主要靠四肢的肌肉運動來產生推力。當梭子魚憑借其寬大的尾鰭形成巨大的推力時，我們人類卻只能依靠自己相對弱小的雙手來產生游動所需的大部分推力。

如果我們來對比一下將代謝中消耗的能量轉化為有用功——這里指產生推力——的能力的話，那么人類在水中只有5%的能量能有效轉化為推力，而魚類、海獅及海豚的能量轉化率卻介于15%~30%之間。

最終，在這場假想的動物奧運會上，人類沒能奪得一枚金牌。我們該為此而感到絕望嗎？杜克大學的生物學家史蒂文·沃格爾并不這樣認為。相反，他認為這其中有些合乎情理?！拔覀儫o法戰勝職業選手，”他說，“但另一方面，其他動物沒有哪一種能夠參加所有的奧運賽事。我們會游泳、爬樹、跑步，只是沒法和這些特長家們比。我們是多面手，我們生來就有了不起的行為多樣性?！?/p>