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为什么人类不长尾巴? – 译学馆
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为什么人类不长尾巴?

Why Humans Don’t Have Tails

解说者:尾巴就像观点
Narrator: Tails are like opinions.
基本上每个生物都有
Basically, everyone has them.
鱼 鸟 大多数爬行动物
Fish, birds, most reptiles,
甚至人类的一些近亲
and even some of our closest relatives.
但为什么人类没有呢?
So why are we missing out?
尾巴首次进化是在五亿年前
Since tails first evolved at least 500 million years ago,
它们扮演了你能想象的所有角色
they’ve taken on every role imaginable.
壁虎用尾巴来储存脂肪
Geckos use them to store fat.
鸟用尾巴来控制飞行方向
Birds use them to steer through the air,
响尾蛇用它来吓退捕食者
and rattlesnakes use them to scare off predators.
但对大多数哺乳动物来说 它有一个主要功能:
But for most mammals, they serve one major purpose:
平衡
balance.
可是 当物种进化接近人类时
Yet, as you get closer to humans on the evolutionary tree,
尾巴消失了
tails disappear.
大猩猩没有尾巴
Gorillas don’t have them,
黑猩猩和猿猴也没有尾巴
and neither do chimps or any other apes,
当然也包括我们人类
including us, of course.
要知道这一原因就得看看我们是怎么行走的
To understand why, take a look at how we walk.
我们中的一些灵长类屈膝
Some of us primates crouchwith our chest
胸部与地面呈对角行走
held diagonally to the ground.
另外像长臂猿和人类能完全直立行走
Others like gibbons and humans can walk completely upright.
现在 这样行走给了我们极大的优势
Now walking like this gives us a huge advantage
因为不像四足动物
because unlike four-legged animals,
它们每走一步都要花费力气
which have to pour energy into every step they take,
两条腿受重力作用
two legs take advantage of gravity,
为我们省了力气
which does some of the work for us.
你看 我们每走一步
You see, each time we take a step,
重力把我们向前拉
gravity pulls us forward.
结果是当我们行走时
The end result is that when we walk,
比四足行走要省25%力气
we use around 25% less energythan walking on all fours.
在野外 你省下的每股力气
And in the wild, every ounce of energy you save
构成了生存和饿死之间的差别
can mean the difference betweensurvival and starvation.
但这种行走方式也完全消除了尾巴存在的必要
But this way of getting around also totally eliminates the need for a tail
因为虽然人类的头部足足有5千克重
because even though a human head weighs a hefty 5 kilograms,
但是当人行走的时候 头部是在身体上方
it sits on top of the body when you walk,
不是在前方
not in front,
所以不需要尾巴来平衡身体
so you don’t need a tail as a counterbalance.
很失望 对吗
Pretty disappointing, huh?
话虽这么说 有过一段时间
That being said, you can still see a reminder of a time
我们的灵长类祖先还是有尾巴的
when our ancient primate ancestors had one.
看看人类的脊椎
Just look at a human spine.
可以看到最后几节骨头
You can see how the last few bones
部分粘合在一起了
are partially fused together.
那是你的尾椎骨
That’s your tailbone.
我们的尾巴就剩这么点了
It’s all that’s left of our tail, and,
对 很悲伤很可怜 你不能摇尾巴
yes, it’s sad and pathetic, and you can’t wag it.
在极少数情况下
Now in rare cases,
婴儿出生时有带像尾巴的东西
babies are born with what looks like a tail,
但那不是尾巴
but that’s not what’s really going on.
很多时候 这些尾巴都是肿瘤
Most often, these tails are actually tumors,
囊肿 甚至是寄生双胞胎
cysts, or even a parasitic twin.
更罕见的情况是
Even more occasionally,
它们是脊椎的真正分支
they’re a true outgrowth of the spine
但它完全没有骨头
but are completely boneless,
它是一条由脂肪和组织构成的软管
a soft tube made entirelyof fat and tissue.
通常 这种类型的尾巴是出生缺陷
These types of tails usuallyform as a birth defect,
是一种叫脊柱裂的脊椎畸形
a deformity of the spinecalled spina bifida.
在这些情况下
And in these situations,
医生们会动手术把尾巴除掉 手术对婴儿无害
doctors will surgically remove the tails with no harm to the baby.
有多一条肢听起来很酷
But as cool as it might sound to have an extra limb
可以在树上荡来荡去或赶走蚊子
to swing through the treesor keep mosquitoes away,
但是我们之所以成为现在的样子
we are who we are today because,
就是因为我们没有尾巴
well, we don’t.

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为什么人类不长尾巴?

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视频来源

https://www.youtube.com/watch?v=DxkukU3HsI8

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