A young white-handed gibbon in South Korea. (EPA/JEON HEON-KYUN)

One of the most defining traits of humanity — our capacity for language — also presents one of our longest-lasting mysteries: How did we begin to talk? And where? And to what end?

Two professors at the Massachusetts Institute of Technology think they have perhaps answered that question in a new study published this week in Frontiers in Psychology. “How did human language arise? It’s far enough in the past that we can’t just go back and figure it out directly,” MIT linguist Shigeru Miyagawa, the lead author on the study, told his university press office. “The best we can do is come up with a theory that is broadly compatible with what we know about human language and other similar systems in nature.”

A system like one found on the island of Java in Indonesia perhaps taught humans to talk 100,000 years ago. On that island resides the silvery gibbon, an endangered primate who inhabits the trees.

The gibbon is a howler. It emits keening shrieks that can hit as many as 14 notes and convey signal territory and send messages to its mate and family members. Its communication is lexical in nature, meaning that it carries meaning, the scientists suggest. It hints at how humans first learned how to talk, and could represent an antiquated form of communication that gave birth to modern language.

But there’s also the expressiveness of language — the lilt of a question, the undulations of tonal tongues. The gibbon doesn’t have that.

What does: the birds.

The ability to communicate ideas, researchers say, comes from primates.

But the melodic side of language derives from birds. Together, both attributes found in totally separate species fused in the past 100,000 years to forge humanity’s capacity for speech.