The blue-eyed Madagascar lemur is sure to elicit a chorus of coos from kids and adults alike, but for human infants it goes beyond being swayed by the cuteness.

When babies are 3 months old, they pay as close attention to lemur calls as they do to human voices.

Earlier studies have shown that infants have deep cognitive engagement when they hear human speech, which makes sense. But now researchers have found that sounds from the blue-eyed Madagascar lemur engage babies in the same way.

“In what may be a hallmark of our ancestry, human brains begin life hard-wired to hear the calls of non-human primates,” reports NBC News.

In the earliest months of life for human babies, "twin engines of development" (nature and nurture) are at work, explains Sandra Waxman, professor of cognitive psychology at Northwestern University and a co-author on the new study.

Waxman and her team studied 72 infants between the ages of 3 and 6 months to see how they responded to four types of sound: high-pitched baby talk, lemur calls, human speech played backward, and mechanical sounds. The responses were clear.

"They were doing some much fancier cognitive dancing during the lemur and human vocalization than in the case of backward speech or tones," Waxman explained. 

But by the time babies reach 6 months, their interest in the sounds of the wee arboreal primates fades away. Since it's the human voices that stay relevant in their lives, they seem to have little need for the “nature” part of the development.

But what if the call of the lemur were to remain a part of our environment; would we retain our primal engagement to the sounds of non-human primates?

The answer may be forthcoming; another study at Waxman's lab will investigate if babies retain their sensitivity to lemur calls when their parents play the sounds every evening at bedtime.

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Why babies love the call of the lemur
In a new study, lemur sounds engaged infants on a cognitive level as much as human sounds did.