哈密尔顿推测，当这片内陆海退去，亚马逊河豚在流域留了下来，逐渐进化为一种恐怖动物。
When this inland sea retreated, Hamilton hypothesizes, the Amazon dolphins remained in the river basin, evolving into striking creatures.
狼不具备这种能力，这说明，狗在从它的先祖，狼科中分离出来起就逐渐进化出了这种能力。
Wolves don’t have the skill, suggesting that it has developed in dogs since the time they branched off from their evolutionary predecessors.
如果属实，那就应该有可能找到从观察模仿我们的灵长类近亲用叫声或手势交流而逐渐进化到人类语言过程的痕迹。
If so, it should be possible to find clues about how human language evolved from grunts or gestures by observing the communication of our close primate relatives.
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