Green and vervet monkeys live on either side of Africa and their evolutionary paths diverged 3.5 million years ago, and yet the two species share a hard-wired vocabulary when faced with danger, clever experiments have shown.

The new research, published Monday, sheds light not only on how primates respond to threats, but also on the building blocks of language itself.

Vervet monkeys in the savannah of east Africa utter three distinct cries depending on whether they spot a leopard, a snake or an eagle, their three main predators.

Fellow monkeys who hear the cries but cannot see the peril react accordingly: the leopard call sends them scurrying up a tree, a snake call prompts them to stand motionless on two legs, and the eagle cry makes them scan the sky while seeking shelter. These unique warning cries sparked debate as to whether they were like primitive words.