The tender interactions between mothers and newborns might not be limited to humans, scientists report.

科学家发现，母亲和新生儿亲密的相互作用可能不仅仅局限于人类。

The intense interactions only last for about a month

Researchers have discovered that the way rhesus macaque（恒河猴） mothers bond with their babies strikes a remarkable¹ resemblance（想象） to human behaviour.

The females make exaggerated facial expressions, kiss-like contacts and gaze intently at their babies.

The study, published in Current Biology, could help trace the origins of the mother-infant bond.

The researchers studied 14 mother-infant pairs over the first two months of their lives at the National Institute of Health's (NIH) primate² centre in Maryland, US.

Professor Pier³ Ferrari, from the department of functional⁴ and evolutionary⁵ biology at the University of Parma, Italy, and the laboratory of comparative ethology at NIH, said: "We started to see that mothers had a very rich way of communicating with their infants."

The researchers found that the mothers would gaze intently at their newborns, sometimes even taking their baby's face with their hands and gently pulling it towards them to get an even closer look.

They would also engage in "lipsmacking" - an affectionate（情深的，充满情爱的） form of expression, where the macaques rapidly open and close their mouths.

Professor Ferrari added: "They also touch the infant's face with their mouths - as if they are trying to remove something.

"And this very much resembles（相似，类似） the kiss that we have in our own species.

"Possibly the evolution of the kiss might have originated from this kind of interaction."

And just as human babies respond to their mother's behaviour, baby macaques would react by returning their mother's gaze, or responding to lipsmacking with a similar gesture.

"The infant is not just a passive subject," Professor Ferrari told BBC News.

Short lived

However, unlike in humans, the researchers discovered that after approximately one month, the mother-infant exchanges in macaques became much less frequent or stopped.

Professor Ferrari said this could be down to the fact that macaque babies develop much more quickly than human babies; a two-week-old macaque baby is very roughly comparable to one-year-old human baby.

He added: "Independence from the mother occurs very early."

Professor Ferrari said that for years this kind of mother-baby interaction was thought to be a uniquely human trait - although more recently, some studies have suggested chimpanzees（黑猩猩） also share some of these emotional interactions with their babies.

He said: "Instead, we can trace the evolutionary foundation of those behaviours, which are considered crucial for the establishment of social exchange with others, to macaques."

Further study of macaques, he added, could help to shed light on（照亮，阐明） why these kind of interactions are important and also how they came about.