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All this is problematic enough when you are the intellectual master of the planet,but when you are a small, vulnerable australopithecine, with a brain about thesize of an orange, the risk must have been enormous. Absolute brain size doesnot tell you everything-or possibly sometimes even much. Elephants and whalesboth have brains larger than ours, but you wouldn't have much troubleoutwitting them in contract negotiations. It is relative size that matters, apoint that is often overlooked. As Gould notes, A. africanus had a brain ofonly 450 cubic centimeters, smaller than that of a gorilla. But a typical africanus male weighed less than a hundred pounds, and a female much lessstill, whereas gorillas can easily top out at 600 pounds (Gould pp. 181-83).
即使在今天，當你已經成為這個星球的智力發達的主人時，這一切依然是個大問題。而對于矮小而又容易受到傷害的南方古猿來說，嬰兒降生時的腦大約有一只柑橘那么大（注：誠然，腦的絕對大小并不能說明一切——有時甚至不能說明很多。大象和鯨的腦都比我們大，但是和它們相比你顯然聰明許多。腦的大小只是一個相對重要的數據，一個常?？梢院雎圆挥嫷臄祿Ｕ绻艩柕滤赋龅哪菢樱显撤侵薹N的腦只有450立方厘米，比大猩猩的要小。而一個典型的南猿非洲種體重小于45千克，女性則更輕，而大猩猩的體重則大都重達150多千克。），危險性肯定很大。
Sowhy did Lucy and her kind come down from the trees and out of the forests?Probably they had no choice. The slow rise of the Isthmus of Panama had cut theflow of waters from the Pacific into the Atlantic, diverting warming currentsaway from the Arctic and leading to the onset of an exceedingly sharp ice agein northern latitudes. In Africa, this would have produced seasonal drying andcooling, gradually turning jungle into savanna. "It was not so much thatLucy and her like left the forests," John Gribbin has written, "butthat the forests left them."
因此，露西和她的同類從樹上來到地上，而后又走出非洲叢林，這是為什么？他們很可能別無選擇。巴拿馬地峽的慢慢上升阻斷了太平洋的海水流進大西洋，改變了流向北極的暖流的方向，使得北緯地區出現了異常寒冷的冰川期。在非洲，季節性干燥和寒冷氣候的出現逐漸使得森林變成了草原。“與其說露西和她的同類離開了森林，”約翰·格里賓寫道，“不如說是森林離開了他們?！?/p>
