Why Do Animals Have Tails?为什么动物有尾巴？

Scientists have found fossils of animals with tails dating back hundreds of millions of years. Back then， early fish used their tails as fins to swim through oceans， and avoid enemies. As these fish developed into creatures that lived on the land， their tails started to change too.

Scientists believe that dinosaurs swung their tails side to side to balance their heavy heads and bodies while walking on two legs. This movement allowed them to run fast enough to catch their prey. Similarly， present-day kangaroos use their tails for balance. But their tail isnt just for balance—it also works as a powerful third leg that can help push them forward through the air. In addition， a monkeys tail can also act like a hand， allowing it to hold onto tree branches.

科学家们发现的有尾巴的动物化石，其历史可以追溯到数亿年前。那时，早期的鱼类用尾巴作为鳍在海洋中游动和躲避天敌。随着这些鱼进化成为生活在陆地上的生物，它们的尾巴也开始发生变化。

科学家们认为，恐龙用两条腿走路时，尾巴左右摆动，是为了平衡沉重的头部和身体。这种动作使它们在抓捕猎物时能够跑得足够快。与之类似的是，现在的袋鼠也用尾巴来保持平衡。但它们的尾巴不仅仅是用来保持平衡——它还可以作为有力的第三条腿，帮助它们腾空前行。此外，猴子的尾巴也可以像手一样，让它能够抓住树枝。

Many insects also have tails. But their roles are quite different. Most tailed insects use their tails to lay eggs.

Birds use their tails both to balance while sitting on trees and to control directions and reduce drag while flying. Some birds also use their tails for mating. Take peacocks for example. Male ones will spread their colorful tails to attract female ones.

Besides， animals that live in groups， like wolves， use different tail positions to show their rank.

Although humans dont have tails like monkeys， our ancestors did have tails. Scientists believe those tails disappeared from our human ancestors around 20 million years ago. Once they started walking upright， they no longer needed tails to help with balance.

许多昆虫也有尾巴，但它们的作用却截然不同。大多数有尾昆虫用尾巴产卵。

鸟类在树上时用尾巴保持平衡，在飞行时用尾巴控制方向和减少阻力。有些鸟类也用尾巴来求偶。以孔雀为例，雄孔雀会展开它们多彩的尾巴来吸引雌孔雀。

此外，群居动物，比如狼，它们的尾巴放在不同的位置就表示不同的等级。

虽然人类不像猴子那样有尾巴，但我们的祖先确实有尾巴。科学家们认为，大约在2 000万年前，我们的人类祖先身上的尾巴就消失了。一旦开始直立行走，他们就不再需要尾巴来帮助保持平衡。

Word Bank

prey /pre?/ n. 獵物

drag /dr?ɡ/ n. 空气阻力

attract /?'tr?kt/ v. 吸引

What first attracted me to her was her sense of humor.