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听力文稿 ( Transcript )
It's the change in the teeth that signals the separation of the line that leads to man. This creature is forty million years old and we only have pieces of the jaw, but it's clear that the teeth are level and more human, there is now a blank in the fossil record for about ten million years, then perhaps five million years ago, we come certainly to the relatives of man. This is a cousin of man, not in the direct line to us, a heavily built Australopithecus who is a vegetarian. The teeth that survive are pitted by the fine grip that he picked up with the roots that he ate. He's cousin on the line to man, he's lighter, visibly so in the jaw, and he's probably a meat eater. This is the nearest thing to what used to be called the missing link ,Australopithecus from Africa, a grown female, the Tang child with which I began this program would have grown up to be like this, fully erect ,walking ,and with a large brain between a pound and a pound and a half, that's the size of the brain of a big ape now ,but of course ,this was a small creature, standing only four feet high.
Indeed, recent finds by Richard Leakey suggest that by two million years ago, the brain was larger even than that ,and with that larger brain, the ancestors of man made two inventions, for one of which we have visible evidence, and for the other inferential evidence. First, the visible invention. Two million years ago, Australopithecus made stone tools like this where a simple blow has put an edge on the pebble, and for the next million years, man in his further evolution didn't change this type of tool. The ancestors of man had a short thumb, so they could only hold this tool in a power grip, and use it like that. It's a meat eater's tool.
The other invention is social. Skulls and skeletons of Australopithecus that we've found in largish numbers show that most of them died before they were 20. That means that there must have been many orphans, and Australopithecus must have had a long childhood as all the Primates do. By the age of ten, they were still children, therefore, there must have been a social organization which adopted them, made them part of the community, educated them. That's a great step towards culture evolution.
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