生命的进化（1979）

进化和变异
尽管那些动物不同
Although all those creatures are different,
但事实上它们之间都是有密切关系的。 它们都是哺乳动物
they are in fact closely related to one another. They are all mammals.
但是它们怎么变得如此不同呢？
But how have they become so varied?
它们的祖先是什么样子的， 最基本的问题是，为什么它们全都不同呢？
And what is the ancestral form, the basic theme, on which they are all variations?
你可以在南亚的雨林里找到非常相似的例子
You can find a close approximation to that theme in the jungles of South-East Asia.
被恰当地叫树鼩
It's properly called a tupaia,
哺乳动物，有像外衣一样的毛发 去保持温暖的体温
and it's certainly a mammal, with a hairy coat and warm blood.
但是是什么种类呢？ 它看起来像松鼠
But what kind? It looks very like a squirrel.
仔细观察它的构造可以发现它类似于兔子
A close look at its anatomy reveals resemblances to a rabbit,
但是它不嚼坚果也不啃草，它抓昆虫
but it doesn't gnaw nuts and it doesn't nibble grass, it catches insects.
它的牙齿小而多，长而尖，就像老鼠的一样
Its teeth are small, numerous and spiky, like a shrew's.
实际上，它普遍的名字叫树鼠
Indeed, its popular name is tree shrew,
但是它那庞大的脑容量和带爪的前腿
but its large brain and those grasping hands
暗示着它们与猴子的关系
have suggested to some that it's related to monkeys.
实际上不同的哺乳动物都有这种印记
It seems in fact to contain hints of many different mammals.
然而有一件事情是清楚的
One thing, though, is clear.
它们非常像早期的哺乳动物
It's very like the earliest of mammals,
生活在一亿年前恐龙消失在地球上的时候
that were living when the dinosaurs dominated the earth 100 million years ago.
最基本的类型已经有很多种
The basic pattern on which there's been such a multitude of variations.
有些种类是如此特别以至于让人很难相信
Some of those variations are so extreme that it's difficult to believe
它们和基本的种类的任何联♥系♥
there's any connection between them and the basic theme,
要没有化石证据和活的动物的解剖的话
were it not for the evidence of fossils and the anatomy of the living animals.
树鼠连续的行动和重复的动作 是哺乳动物的象征
The tree shrew's continuous activity and swift reactions are typical of a mammal.
结果是在它们的身体里产生热量
A consequence of its ability to generate heat within its body
并使身体中的化学反应更快，提供充裕的能量
so that its chemistry works fast and provides it with abundant energy.
这种能力可能产生于很久以前
This talent probably developed a very long time ago indeed,
恐龙占统治地位的那个时代
at a time when the dinosaurs dominated the earth.
因为动物的化石和现在活着的树鼠非常相似
For fossils of a creature remarkably similar to the living tree shrew
在那些已经被发现的距今两亿年的石头里
have been found in rocks that are 200 million years old.
那些长而尖的牙齿说明它是以昆虫为食的
Its numerous spiky teeth suggest that it ate insects,
成形的下肢说明它是一个迅速的奔跑者
and the shape of its limbs that it was a swift runner.
实际上，它的生活方式与树鼠不一样
In fact, its lifestyle was not unlike a tree shrew.
像它这样的动物生活在恐龙的身旁， 遍及恐龙统治时期
And creatures like it survived alongside the dinosaurs throughout their reign,
可能在晚上到处奔跑
probably scampering about at night
在恐龙也变得行动迟缓的冰期时代
when the colder-blooded dinosaurs became torpid in the cold.
然后，在6千5百万年前连恐龙也消失了
Then, 65 million years ago, the dinosaurs disappeared.
整个地球的森林和沼泽再也没有任何动物
The forests and swamps of the world were suddenly empty of large creatures.
原始的鸟在天空中拍打着翅膀
Primitive birds flapped through the sky,
但是在陆地上没有任何动物 除了昆虫和那些无脊椎动物
but on the ground there were few creatures other than insects and other invertebrates
那些原始的小型哺乳动物以它们为食
and those small warm-blooded primitive mammals that fed on them.
在世界上任何一个不定的角落
And here and there, in odd corners of the world,
它们的子孙仍然生存着，没有改变
their descendants still survive, little changed.
马来西亚的树鼠就是其中之一
The tree shrew of Malaysia is one.
在比利牛斯山某处生活着一种鲜为人知的种类
Here in the streams of the Pyrenees lives another little-known and very engaging one.
名叫尘香鼠
It's called a desman.
和大多数原始的哺乳动物一样 尘香鼠有着惊人的食欲
Like most of these primitive mammals, the desman has a stupendous appetite.
每天它要吃相当于它们体重三分之二的食物
It eats two-thirds of its own body weight every day
好像从来没有停止过捕食一样
and seems never to stop the hunt for more.
它的鼻子成为它们最主要的寻找食物的工具
Its nose does most of the searching.
它用鼻孔嗅水中微弱的气味
It scents the faintest changes in the taste of the water with its nostrils,
它会用胡须来感觉周围的路
and feels its way around with all those whiskers.
它的脚爪带有蹼，可以用来游泳和爬山
Its feet are a combination of web and claw, for both swimming and clambering.
它的眼睛很小，眼珠藏在长毛下
Its eyes are tiny, minute beads hidden in its long fur.
当它们发现好的食物，它不会轻易放弃
When at last it does find something good, it doesn't give up easily.
通气管一样的鼻子允许它全力吸一口气
Its snorkel nose allows it to snatch a breath
以最小的争斗时间间隔
with the minimum of interruption in the struggle.
为了捕获蠕虫它可以坚持几个小时
Its hard-fought-for worm will now keep it going for another hour or so.
另外一种这样的原始幸存者 生活在北美的一些河流
Another of these primitive survivals lives along the streams of North America.
它不但是有耐力的水手还是挖洞高手
It's not only an energetic swimmer, but a burrower as well.
它的游泳方式以及身体结构
It's possible the swimming way of life and the body design to go with it
决定了类似的行为， 不是在水里而是地面下
led to a similar activity not in water, but underground.
它的划浆就变成了铁铲
What were paddles have become spades.
这是星鼻鼹鼠
This is the star-nosed mole.
鼻子上奇怪的肉花就是高度敏感的侦察器
The odd fleshy flower on its nose is another highly sensitive smelling device.
也许还有其他方法去侦察周围的环境
It may have yet another way of investigating its surroundings.
大多数食昆虫的动物，像地鼠
Many of these little insect-eaters, such as shrews,
用我们听不到的高频率的声音
make squeaks so high-pitched that we can't hear them,
它们制♥造♥的这种声音可以使附近的动物找到路
and the echo they produce helps the animals to find their way around.
鼠类，像厅香鼠和地鼠，有着惊人的食欲
Moles, like desmans and shrews, have formidable appetites
它们每一分钟都在吃东西
and have to eat every few hours.
它们的食道不仅是食物的入口还可以贮存食物
Their tunnels are not simply passageways, but traps.
把从土壤里挖出来的蚯蚓和昆虫吸进去
Worms and insects burrowing through the soil drop into them,
它收集任何发现的昆虫
and the mole collects whatever turns up.
如果它的食欲即刻得到满足
If its appetite is momentarily sated,
它会把剩余的昆虫咬得麻痹 然后贮存在一个特殊的地方
then it paralyses a surplus worm with sharp bites and stores it away in a special larder
再一次动身前，它会不停地查看
before setting off again on its never-ending patrols.
各种小型的以昆虫为食的动物
Variations on the theme of the small insect-eater
在恐龙消失以后就不断地出现
began to appear soon after the dinosaurs vanished.
动物在不断的发展， 尤其是有一种以蚂蚁和白蚁为食的
Creatures developed that specialised in feeding on one kind of insect: ants and termites.
那是另外一种掘地兽，从非洲来的土豚
This is another digger, the aardvark, from Africa.
它是南美大型食蚁动物的同类
And this is its South American equivalent, the giant anteater.
对于以蚂蚁和白蚁为食的动物来说， 它们的相同点是
The essential equipment for a diet of ants and termites, it seems,
有伸长的嘴可以钻进昆虫的巢穴里
is an elongated snout for poking inside the nests
还有长长的粘舌头收集虫子
and a long sticky tongue for collecting the insects.
有一种最极端的现存的巨型食蚁兽
And the giant anteater has the most extreme version of both that exists.
白蚁最容易被咬碎，
Termites are easily crushed,
所以食蚁动物不必有牙齿， 并且失去了全部牙齿
so the anteater has no need of teeth and has lost them all.
然而，白蚁的巢穴可能像水泥一样牢国
Termites' nests, however, can be as hard as cement,
需要强有力的爪和腿打开它
and strong claws and muscular legs are needed to tear them open.
食蚁动物对食物非常挑剔。 尽管它的名字叫食蚁动物，但它很少吃蚂蚁
The anteater is very fussy about its food. In spite of its name it seldom eats ants.
实际上像这些白蚁是一种更平常的食物
Termites, like these, are a much more usual meal,
尽管如此，它还是喜欢白蚁甚过其它
and even then it prefers some termites to others.
世界上这类哺乳动物的种类有几十种
There are a dozen or so species of mammal round the world
专门以蚂蚁和白蚁为食
that have specialised in living on ants and termites.
作为一种生活方式看起来好像
As a lifestyle it doesn't seem to require
不需要特别快的反应和积极地部署
a particularly quick intelligence or vivacious disposition.
所有这些食蚁动物都是相对动作缓慢的动物
And all these anteaters are relatively slow-moving creatures.
由于这一点以及它们都没有牙齿，
Because of that and their total lack of teeth,
对于猎手来说，它们可能看起来容易捕捉
they might seem to be easy meat for a hunter.
但是，巨型食蚁兽的前腿如此有力 以至于它的拥抱是致命的
But the giant anteater's front legs are so strong that its hug is lethal,
几乎没有动物打扰它
and few creatures interfere with it.
有一种生活在非洲的食蚁动物，穿山甲
The termite-eating specialist of Africa, the pangolin,
它非常小，也不是一个很强的掘地兽
is much smaller and not nearly such a powerful digger.
有柔韧的鳞片盔甲
It's developed a flexible armour of scales
可以把自己卷成一个球，以至于不易受到攻击
and can curl itself up into a ball so that it's virtually impregnable.
它有力的尾巴就像平衡木一样
Its muscular tail also acts as a counterbalance
以至于它能用后腿 支撑身体的大部分重量而行动
so that the creature can trundle along with most of its weight on its back legs,
而它的前腿则用来挖白蚁堆，就像这样
and its front legs at the ready for digging into termite mounds, like this one.
它对自己的防御能力如此自信 以至于它几乎不关心在它周围的任何动物
It's so confident of its defences that it takes little notice of any other creature around,
除非它们主动骚扰它
unless they molest it.
最小的是南美的侏食蚁兽 (又称丝食蚁兽、姬食蚁兽)
Smallest of all, the pygmy silky-furred anteater of South America.
看起来完全没防卫能力，也不能很快地移♥动♥
It does seem to be defenceless and can't move fast enough
来逃脱笨拙的猎手
to escape even the clumsiest hunter.
但是它能在树枝间自♥由♥移♥动♥， 并完全以树上的蚂蚁为食
But it keeps out of the way up in the branches, living almost entirely on tree ants.
不管是雄的还是雌的， 它的背上部有一个小食蚁兽
This one has a baby on its back, and it may be either male or female,
作为父母，它们共同分担生活的担子
for both parents take a share in carrying the load.
在南美，还有另外一种很特别的食蚁动物
There's yet another kind of specialist anteater in South America,
介于前面二者之间：小食蚁兽
intermediate between the giant and the pygmy: the tamandua.
它大多在晚上捕食
It feeds mostly at night.
它们用厚厚的，像钢针一样的毛来保护自己
Its thick, bristly fur is supposed to protect the tamandua
而不被从已经损坏的蚁窝里蜂拥而出 并且发狂的蚂蚁咬伤
from the bites of infuriated ants, swarming from their shattered nest.
但是，当你观察它进食的情况时
But when you watch the animal feeding,
你禁不住会想，它的保护真地有用吗？
you can't help wondering just how effective that protection really is.
蚂蚁和白蚁是数量最多的昆虫， 尤其是在热带地区
Ants and termites are among the most numerous insects, particularly in the tropics.
食蚁兽和它的同类则分布于全世界
And the tamandua and its relatives around the world
它们没有困难去找到足够的食物
have little difficulty in finding more than enough to eat.
并且昆虫不但在水里，在土壤里，在植物上，
And there are insects not only in water and in the soil and all over plants,
而且在空中，尤其是晚上
but in the air, and particularly at night.
很难知道到它们有多少
It's difficult to realise just how many there are
除非你举着一个水银蒸气灯在热带地区