一旦语言从2岁左右开始发展，他们就有了一个符号表征系统，可以谈论过去和现在环境之外的事情。

Once language starts to develop from about age 2, they do have a system for symbolic representation and can talk about things which aren't in their immediate environment including the past.

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在上世纪六十年代以前，语言的符号表征一直被视为是人类的专利。

Until the 1960s, symbolic representation of language was thought to be uniquely human.

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早在2004年，麻省理工的这个研究小组就报道说，亚马孙Piraha人的语言似乎只能表达“1、2和许多”三个概念，而无法对超过2的数进行精准表征。

Back in 2004, the M.I.T. team reported that the Piraha people seemed to have terms that described “one, ” “two, ” or “many.”

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