Why Can't Monkeys Talk?

Decades ago, while Philip H. Lieberman was soaking in a bathtub and listening to the radio, he heard anthropologist Loren Eiseley ponder an evolutionary puzzle: Why couldn't monkeys talk?

Like us, they're social primates, intelligent and certainly not quiet. Rhesus macaques grunt, coo, screech and scream. Infant macaques make sounds known as geckers.

Despite the grunting and geckering, though, no other primates - not even the chimpanzees and bonobos, our nearest ape relatives - can make the vowel and consonant sounds we know as speech.

Scientists figured there were two likely sticking points. Either the brain was not wired for speech in nonhuman primates, or their windpipes were shaped the wrong way.