because there's no fossil record of verbal communication for scientists to look back through.因为并没有记录语言交流的化石供科学家来回溯过去

look back回顾； 回头看

She looked back over a distance of ten years.

她回顾过去十年的时间。

How do you look back on your time at Liverpool?

你怎样回头看你在利物浦的职业生涯？

Mark Pagel is an evolutionary biologist on the hunt for the origins of language.马克·帕杰尔是位进化生物学家专门寻找语言的起源

on the hunt寻找

The police are on the hunt for further clues.

警方正进一步寻找线索。

The company is on the hunt for a personnel manager.

这个公司在招聘一名人事经理。

but they rely on having the right genetics in place但他们都依赖于适当的基因

rely on 依靠；信赖

Don't rely on him to do anything he's just a talker.

什么事都不要依靠他－－他光会说空话。

Now that you are grown up, you should not rely on your parents.

既然你长大了，就不应该依靠你的父母。