36套exercise13的一题

canie.duUID: 3453356

Biologists have long maintained that two groups of pinnipeds, sea lions and walruses, are descended from a terrestrial bearlike animal, whereas the remaining group, seals, shares an ancestor with weasels. But the recent discovery of detailed similarities in the skeletal structure of the flippers in all three groups undermines the attempt to explain away superficial resemblance as due to convergent evolution—the independent development of similarities between unrelated groups in response to similar environmental pressures. Flippers may indeed be a necessary response to aquatic life, turtles, whales, and dugongs also have them. But the common detailed design found among the pinnipeds probably indicates a common ancestor. Moreover, walruses and seals drive themselves through the water with thrusts of their hind flippers, but sea lions use their front flippers. If anatomical similarity in the flippers resulted from similar environmental pressures, as posited by the convergent-evolution theory, one would expect walruses and seals, but not seals and sea lions, to have similar flippers. (162 words)

不太明白文章最后一句话。为什么说，如果趋同进化是对的话，人们应该期待walruses和seals相似，而非seals和sea lions相似。可是上一句话讲的就是walruses和seals相似呀（都是hind flippers, 而sea lion是front flippers嘛）。

canie.duUID: 3453356

wcjjudy 发表于 2016-8-15 16:13
最后一句是虚拟语气，那么实际的意思就是字面意思取反。 如果相似性是由covergent evolution决定，那么w和s ...

明白了哦！谢谢! 所以是说新观点错 旧观点对撒