We think that the smaller digestive system in Homo erectus was able to evolve because of the shift in diet,我们认为，正是食物的转变使直立人的消化系统得以进化

able to能做 ...

I may be able to help you in some way.

我也许可以从某个方面去帮助你。

He was able to cast off such an uninteresting task.

他终于摆脱了这么一项乏味的工作。

because of因为； 由于

We win the game because of his participation.

由于他的参与，我们赢了比赛。

Because of his irresolute character, we were defeated at last.

因为他性格的软弱，我们最终被打败了。