生命的进化（1979）

当这个怪物的标本在18世纪末叶 从澳大利亚第一次
When specimens of this creature first reached Europe from Australia
送到欧洲的时候人们都不敢相信自己的眼睛
at the end of the 18th century, people refused to believe their eyes.
人们深信这只是一个骗局
They said it was a hoax.
它只是一个由不同动物的残肢碎片 拼凑而成的怪物
Bits and pieces of different creatures rather crudely sown together.
但这不是骗局，它只是一只鸭嘴兽而已
But it's no hoax, it's a platypus.
但从某方面来讲， 人们原先的的怀疑也不无道理
And yet, in a way those early sceptics were right.
鸭嘴兽的确是最奇怪的 具有不同动物体特征的动物
The platypus is the most extraordinary mixture of different animals.
它既是哺乳动物又是爬行动物
It's part mammal and part reptile.
正因如此，它给了我们 哺乳动物进化的一些线索
And so it can give us some idea of how the first mammals developed.
哺乳动物的崛起
鸭嘴兽给人的第一印象是一种普通的哺乳动物
At first sight the platypus looks like a regular mammal.
他毕竟有致密的柔软毛皮 这是所有哺乳动物的特征
It has, after all, dense soft fur, one of the hallmarks of mammals.
当你触摸它时，你能感觉到它的体温
And when you handle it, you can feel that its body is warm.
它的脚是有蹼的，利于游泳，像水獭一样
Its feet are webbed for better swimming, rather like an otter's.
奇怪的嘴不像鸟嘴一般坚硬
The strange bill is not hard, like a bird's beak,
而是柔软富有弹性且十分敏感
but soft, rubbery and very sensitive.
鸭嘴兽的视力十分弱
The platypus, which has poor eyesight, uses it to find its food:
靠它寻找小龙虾和其他水生动物
crayfish and other water-living creatures.
但繁殖的时候
But when it comes to breed,
它做了一件与其他哺乳动物迥异的事
it does something that separates it from all other mammals except one.
在它深处洞穴的巢中下蛋
In its nest, deep in a burrow, it lays eggs.
这使它和爬行动物搭上了关系
It's this that links the platypus with the reptiles,
被冠以现存的最原始的哺乳动物之名
this that entitles it to be regarded as the most primitive living mammal.
正因如此，更加怪异
But, and this is what makes it doubly paradoxical,
蛋孵化以后 鸭嘴兽妈妈不会扔下宝宝不管
when the egg hatches, the young platypus is not left to find food by itself,
像其他爬行动物的孩子们一样， 它的食物由母亲供给
like reptile babies are, but is provided with food by the mother.
像所有的哺乳动物一样，鸭嘴兽
The platypus, like all mammals,
皮肤具备防止体温过高的汗腺
has in its skin, as a mechanism for dealing with overheating, sweat glands.
在它的腹部这些腺体特别大
On the underside of the body these sweat glands are specially big
产生含有脂肪的液体，乳汁
and produce a kind of fatty sweat, which is milk.
它只是简单地从皮肤中渗出 小鸭嘴兽从母亲的毛丛中吮吸
It simply oozes from the skin, and the young suck it from tufts of hair.
因为没有乳♥头♥ 严格意义上讲不能称为乳♥房♥♥
There is no nipple, so it hardly qualifies as a breast, or a mamma, its technical name,
而乳♥房♥♥恰恰是哺乳动物 之所以成为哺乳动物的基本特征
the feature that gives mammals their name.
除了它之外 只有一种哺乳动物没有乳♥房♥♥
Only one other mammal lacks a true breast,
这个就是，针鼹鼠
and this is it, the echidna.
像鸭嘴兽一样，它也生活在澳大利亚，也产卵
It too, like the platypus, lives in Australia, and it too lays eggs,
但是鼹鼠妈妈不会把蛋放在巢中， 而是带在身上
but the female doesn't deposit them in a nest, she carries them with her.
这些蛋的外壳粘粘的， 附着在妈妈腹部临时沟槽的毛上
They have sticky shells and become glued to the hair on her underside
而沟槽横跨在鼹鼠妈妈的腹部
in a temporary groove that develops across her stomach.
每个蛋都不会比豌豆大
Each is no bigger than a pea,
十天后蛋孵化了
and after ten days it hatches.
现在妈妈腹部沟槽两边的腺体
By now, glands on either side of the groove in the mother's stomach
分泌营养丰富的乳汁
are producing rich, creamy milk.
接下来的8周时间针鼹鼠宝宝会呆在凹槽里
The baby echidnas remain inside the groove for the next eight weeks,
不断地吸收乳汁，发育生长
steadily taking in milk and growing.
当刺长起来的时候小家伙成了使人不适的乘客
When the spines develop, the youngsters must become uncomfortable passengers,
妈妈会把它们放在洞穴里面
and their mother deposits them in a den.
最后，它们不吃乳汁，而吃成年针鼹鼠食品
Eventually, they abandon milk and take to their adult diet:
蚂蚁
ants.
像鸭嘴兽一样的长嘴
The long snout, like the platypus' bill,
从进化的角度来说，是新进化的
is, in evolutionary terms, a recent acquisition,
是收集食物的专用工具
a specialised tool for food-gathering.
里面藏着一个长长的粘粘的舌头
It houses a long, sticky tongue,
针鼹鼠用它捕获蚂蚁和白蚁
with which the echidna flicks up its ants and termites.
他用挖洞这种简单的权宜计策保护自己
The animal defends itself by the simple expedient of digging downwards,
一分钟之内，除了尖刺你就什么都看不到了
so that within a minute or so, there's nothing to be seen but spines.
鸭嘴兽和针鼹鼠都是孤立的怪兽
The platypus and the echidna are isolated oddities.
没有化石证据告诉我们它们何时何地进化
We've virtually no fossil evidence to tell us where or when they developed.
一个合理的推测是鸭嘴兽和针鼹鼠起源于此
It's a reasonable guess, because there's another echidna
因为在离这儿北方不远的新几内亚
which lives not far north of here in New Guinea,
有另外一种针鼹鼠
that the group did originate in this part of the world.
毋庸置疑，它们代表了1亿8千万年前
It's absolutely certain, however, that they do represent a group of primitive creatures
现代哺乳动物进化前的原始动物
from which more modern mammals developed about 180 million years ago.
当然，我们可以追溯的哺乳动物的历史 比这更久远
Of course, we can trace back the ancestry of mammals even farther than that.
爬行动物早在三亿年之前就开始进化了
The reptiles had first developed about 300 million years ago.
他们有防水的皮肤，卵生
They had watertight skins and shelled eggs,
所以他们能在干燥的世界里存活
so they could survive in the driest country.
大约两千万年以后
After some 20 million years,
一种移♥动♥迅速的猎食性爬行动物，盘龙诞生了
a group of swift-moving, hunting reptiles evolved called pelycosaurs.
爬行动物不能靠自身产生热量
Reptiles can't generate heat within their bodies,
这意味着经过漫长的寒夜之后
and that means that after a cold night,
他们的行动很迟缓 只能慢慢适应早晨的环境
they are very sluggish and slow to get going in the morning.
盘龙通过进化来的硕大帆状背鳍
Pelycosaurs dealt with that difficulty
来应对这困难
by developing great sail-like fins along their backs
迎接清早的第一缕曙光
to catch the first rays of the morning sun
可以很早地外出狩猎
so they could get out hunting really early.
据此不难想象
In places like this it's easy to imagine
约十二英尺长的的某种盘龙，像异齿龙
some 12-foot species of pelycosaur, like dimetrodon,
趴在晨曦中的石头上晒太阳
lying basking on the rocks in the early morning sun.
由此推断, 通过这些背鳍的帮助
It's been calculated that with the aid of their fins,
它们的体温可以在一小时之内升高约6摄氏度
they could raise their body temperature some six degrees inside an hour,
如果没有这些背鳍这个过程可能长达3小时
whereas without them, it would take nearly three hours.
但是这些背鳍也只是进化中的权宜之计
But those fins were stopgap devices only.
在这之后，盘龙没有背鳍也能做到
Later species of pelycosaurs managed to do without them.
这可能是因为它们自身可以产生热量
That's probably because they were able to generate heat internally,
他们的牙齿证实了这种推测
and their teeth provide evidence which supports that idea.
异齿龙的牙齿 像大多数爬行动物的牙齿一样
Dimetrodon's teeth, like those of most reptiles,
是简单的大钉子，它的功用仅限于捕捉猎物
were simple spikes which did little more than grip a victim.
但是体内产生热量需要大量的能量
But generating heat within the body requires a great deal of energy.
所以温血动物比爬行动物吃的食物多
So a warm-blooded animal must eat much more food than a normal reptile
消化得更迅速
and digest it fairly rapidly.
盘龙牙齿的一代代的进化
Changes in the teeth of successive generations of pelycosaurs
暗示他们正是这么做的
suggest that that is just what they did.
简单的牙齿进化成专门的屠♥杀♥工具
The simple spikes changed into specialised tools for butchery.
上腭的两侧出现了
Daggers appeared on either side of the upper jaw
用来撕开猎物皮毛
for slitting open the hide of the prey,
匕♥首♥状的牙齿 及咬骨头用的牙齿也出现了
knives for slicing the meat and grinders for crunching bones.
大多数爬行动物一生中不断地换掉磨损的牙齿
Most reptiles shed teeth as they become worn sporadically throughout their lives.
但是这些动物的牙齿变得越来越专业和耐久
But the teeth of these creatures became both specialised and permanent,
上下牙啮合得越来越准确 可以更有力地撕咬猎物
and the upper and lower ones meshed accurately to give a highly efficient bite.
自从这些动物自身产生热量之后
Since these creatures generated their heat internally,
它们就需要保暖的皮毛以保存这些热量
they would also have needed a coat of hair in order to conserve it.
哺乳动物出现了
The mammals had arrived.
温暖的血液比简单的快速移♥动♥
The acquisition of warm blood
带给它们更多的好处
brought more advantages to them than straightforward speed of movement.
如果你可以在1亿8千万年前的夜晚，穿越丛林
As you would have seen
你可以亲眼目睹
had you been able to walk through the forests of 180 million years ago at night.
第一个真正的哺乳动物诞生在
The first true mammals appeared
爬行动物统治的世界
at a time when the reptiles ruled the world.
但是那些巨大的太阳能供热动物有一大缺陷
But those great solar-powered animals had one major disability.
当夜幕降临，它们的体温下降，行动变得迟缓
At night, when it got cool, they became sluggish.
这就给了夜间活动的动物袭击它们的机会
That left the field open to any creature that could be active at night.
而哺乳动物依靠它们的温暖血液 正好可以做到这一点
And the mammals, with their warm blood, could do just that.
原始的哺乳动物体型都很小
The ancient mammals were small, nocturnal insect hunters
是主要靠嗅觉来寻找食物的夜间昆虫猎食者
that relied chiefly on their sense of smell to find their food.
事实上，它们与今天的鼩鼱和豪猪 可能非常类似
In fact, they were probably very similar to present-day shrews and hedgehogs,
尽管它们可能依然产卵
although they may have laid eggs.
温暖的身体是它们生存和最终成功的关键
Warmth was the key to their survival and ultimate success.
因为它们可以在寒冷的夜晚独自狩猎
Since they alone could hunt during the cool of the night,
这样就避免了和爬行动物竞争
they didn't have to face competition with reptiles.
这些原始的哺乳动物平安地度过了恐龙时代
Those primitive mammals were able to live right through the age of the dinosaurs
并且为在爬行动物衰落后 接管这个世界做好了准备
and be ready poised to inherit the world when the reptiles finally declined.
保持温暖不仅是成年动物所面临的问题
The problem of keeping warm was one that didn't just face adults,
卵和胚胎同样面临这些问题
it also faced eggs and embryos.
哺乳动物进化出三种不同的方式来应对这些
And the mammals developed three ways of dealing with that.
最原始的方法是孵卵，就像今天的鸭嘴兽
The primitive ones incubated their eggs, as the platypus does today.
其他的哺乳动物进化出更有效率的方法
Other mammals developed more efficient methods.
生活在美洲的负鼠就是一例
The opossum, that lives in North and South America, is one.
它不产卵 但是从交♥配♥到繁殖只有十二天半的时间
It doesn't lay eggs, but gives birth to its young only twelve and a half days after mating.
宝宝可能会有20只之多
There may be as many as 20 of them.
只有蜜蜂大小，他们仅有的成型部位是前腿