because there's no fossil record of verbal communication for scientists to look back through.因為并沒有記錄語言交流的化石供科學家來回溯過去

look back回顧； 回頭看

She looked back over a distance of ten years.

她回顧過去十年的時間。

How do you look back on your time at Liverpool?

你怎樣回頭看你在利物浦的職業生涯？

Mark Pagel is an evolutionary biologist on the hunt for the origins of language.馬克·帕杰爾是位進化生物學家專門尋找語言的起源

on the hunt尋找

The police are on the hunt for further clues.

警方正進一步尋找線索。

The company is on the hunt for a personnel manager.

這個公司在招聘一名人事經理。

but they rely on having the right genetics in place但他們都依賴于適當的基因

rely on 依靠；信賴

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

什么事都不要依靠他－－他光會說空話。

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

既然你長大了，就不應該依靠你的父母。