Nobody knows, but there's a theory which won't answer your question but will put it into a broader context.

没有人知道答案,但有这么个理论,它无法回答你的问题,但却能让你从更宽广的视角来看这个问题

耶鲁公开课 - 心理学导论课程节选

These are all plausible reasons and possible contributors but nobody's got the home run answer yet.

这些原因听起来都很有道理,但还没有人能给出准确的答案

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选

Very good yes, and that's a big argument that nobody has a good answer for.

好问题,还没有人给出令人信服的答案

耶鲁公开课 - 古希腊历史简介课程节选

What extent was the primitive form of Primitive form of what I'm not sure that that concept makes-- No, the answer is no, because nobody was compelled to do anything.

原始形态的比重,什么的原始形态,我不确定那个概念,不,因为没有人被强迫做任何事

耶鲁公开课 - 古希腊历史简介课程节选

Still nobody got the answer.

还是没人想出答案

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选