that there'd be an advantage for speech over sign.

口语比手语更加优越
That sign languages may be full-blown languages

手语或许是成熟的语言
but they just take--they're just harder to learn

但它们更难学
because the brain and the body have adapted for speech.

因为大脑和身体已经适应了口语
It turns out that this just isn't the case.

这不光是一个个案
It turns out that sign and--the developmental milestones of sign languages

手语的发展阶段
and the developmental milestones of spoken languages are precisely the same.

和口语语言的发展阶段是完全相同的
They start babbling at the same point.

婴儿们同时开始咿呀学语
They start using first words,

他们同时使用第一个词
first sentences, first complicated constructions.

第一个句子第一个复杂结构
There seems to be no interesting difference

似乎大脑在如何获得和使用口语语言
between how the brain comes to acquire and use the spoken language

与如何获得和使用手语之间