Then a strange thing happened.
这时，一件神秘的事情发生了。
All the gigantic reptiles died within a short time.
所有这些庞大的爬行动物在短时间内悉数灭绝。
We do not know the reason.
我们不知道其中的原因。
Perhaps it was due to a sudden change in climate.
也许是由于气候的突然变化，
Perhaps they had grown so large that they could neither swim nor walk nor crawl, and they starved to death within sight but not within reach of the big ferns and trees.
也许是因为它们的身体长 得过于庞大，以至行动困难，再不能游泳、奔走和爬行。它们只能眼睁睁地看着肥美的厥类植物和树叶近在咫尺，却活活饿死。
Whatever the cause, the million year old world-empire of the big reptiles was over.
不管出于什么原因，统治地球数百万年的古爬行动物帝国到此就覆灭了。
The world now began to be occupied by very different creatures.
现在，地球开始被不同的动物占据。
They were the descendants of the reptiles but they were quite unlike these because they fed their young from the "mamm?" or the breasts of the mother.
这些动物属于爬行动物的子孙，但其性情与体质都迥异于自己的先祖。它们用乳房“哺事”自己的后代，
Wherefore modern science calls these animals "mammals."
因此现代科学称这些动物为“哺乳动物”。
They had shed the scales of the fish.
它们褪去了鱼类身上的鳞甲，
They did not adopt the feathers of the bird, but they covered their bodies with hair.
也不像鸟儿那样长出羽毛，而是周身覆以浓密的毛发。
The mammals however developed other habits which gave their race a great advantage over the other animals.
由此，哺乳动物发展出另一些比之其它动物更有利于延续种族的习性。
The female of the species carried the eggs of the young inside her body until they were hatched
比如雌性动物会将下一代的受精卵孕含在身体内部，直至它们孵化；
and while all other living beings, up to that time, had left their children exposed to the dangers of cold and heat,
比如当同时期的其它动物还将自己的子女暴露于严寒酷热，
and the attacks of wild beasts, the mammals kept their young with them for a long time and sheltered them while they were still too weak to fight their enemies.
任其道猛兽袭击时，哺乳动物却将下一代长时间留在身边，在它们无法应付各种天敌的脆弱阶段保护它们。
In this way the young mammals were given a much better chance to survive, because they learned many things from their mothers,
这样，年幼的哺乳动物便能得到更佳的生存机会，因为它们能从母亲身上学习到很多东西。
as you will know if you have ever watched a cat teaching her kittens to take care of themselves and how to wash their faces and how to catch mice.
如果你看过母猫是如何教小猫照顾自己，如何洗脸，如何捉老鼠等等，你就能理解这一点了。
But of these mammals I need not tell you much for you know them well.
不过关于这些哺乳动物，不用我告诉你很多。
They surround you on all sides.
它们遍布你的四周，你早已熟悉。
They are your daily companions in the streets and in your home, and you can see your less familiar cousins behind the bars of the zoological garden.
它们是你日常生活的同伴，出没于街道和你家的房屋。在动物园的铁栅栏后面，你还能一睹你那些不太熟悉的表亲们的尊容。
And now we come to the parting of the ways when man suddenly leaves the endless procession of dumbly living and dying creatures
现在，我们来到了历史发展的分水岭。此时，人类突然脱离了动物沉默无言、生生死死的生命过程，
and begins to use his reason to shape the destiny of his race.
开始运用脑子 来掌握自己种族的命运。
One mammal in particular seemed to surpass all others in its ability to find food and shelter.
一头特别聪明的哺乳动物在觅食和寻找栖身之所的技能方面，大大超越了其他动物。
It had learned to use its fore-feet for the purpose of holding its prey, and by dint of practice it had developed a hand-like claw.
它不仅学会用前肢捕捉猎物，并且通过长期的训练，它还进化出类似手掌的前爪。
After innumerable attempts it had learned how to balance the whole of the body upon the hind legs.
又经过无数次的尝试之后，它还学会了用两条后腿站立，并保持身体的平衡。
(This is a difficult act, which every child has to learn anew although the human race has been doing it for over a million years.)
（这是一个非常困难的动作，尽管整个人类已经有上百万年 直立行走的历史，可每一个小孩子在成长过程中都得从头学起。）
This creature, half ape and half monkey but superior to both, became the most successful hunter and could make a living in every clime.
这种动物一半像猿，一半像猴，可比两者都要优越，成为了地球上最成功的猎手，并且能在各种气候条件下生活。
For greater safety, it usually moved about in groups.
为了更安全，更便于相互照顾，它们常常成群结队地行动。
It learned how to make strange grunts to warn its young of approaching danger
一开始，它只能发出奇怪的咕喀声、吼声，以此警告自己的子女们正在迫近的危险。
and after many hundreds of thousands of years it began to use these throaty noises for the purpose of talking.
可经过几十万年的发展，它竟然学会了如何用喉音来交谈。
This creature, though you may hardly believe it, was your first "man-like" ancestor.
你也许觉得难以置信，这种动物就是我们最初“类人”的先祖。