Female monkeys give more attention to masculine males

For male rhesus macaques hoping to woo a mate, it just might help to look a little macho.

While researchers have long suspected that differing facial features among male and female primates of the same species may play a role in mate choice, the draw of ‘facial masculinity’ has remained understudied outside of human subjects.

To better understand how female monkeys perceive these traits, primatologists observed free-range rhesus macaques over a series of ‘looking-experiments.’

The study revealed that the female macaques held their gaze longer when looking at more masculine faces – but, the researchers aren’t exactly sure why.

While researchers have long suspected that differing facial features among male and female primates of the same species may play a role in mate choice, the draw of ‘facial masculinity’ has remained understudied outside of human subjects

While researchers have long suspected that differing facial features among male and female primates of the same species may play a role in mate choice, the draw of ‘facial masculinity’ has remained understudied outside of human subjects

In the new study led by Penn State primatologist and biological anthropologist Kevin Rosenfield, researchers studied rhesus macaques on Cayo Santiago, just off the east coast of Puerto Rico.

The team observed the reactions of 107 female macaques presented with pairs of images of male faces.

In each pair, one face had more masculine features, while the other one appeared more feminine.

It’s thought that facial masculinity may be tied to perception of the male monkey’s overall strength and success in competition, the researchers explain in the paper, published to bioRxiv.

More masculine-looking monkeys had a number of facial features that differed from the other males’, including jaw width, nose length, and lower face height. In these cases, the features were typically larger

More masculine-looking monkeys had a number of facial features that differed from the other males’, including jaw width, nose length, and lower face height. In these cases, the features were typically larger

Strong facial features could be a signal of bite strength, for example.

The researchers measured the faces of male and female monkeys, noting a number of differences between the sexes.

More masculine-looking monkeys had a number of facial features that differed from the other males’, including jaw width, nose length, and lower face height.

In these cases, the features were typically larger.

As the team suspected, the experiments showed females spent more time looking at the more masculine monkeys.

It’s thought that facial masculinity may be tied to perception of the male monkey’s overall strength and success in competition. But, more research is needed to better understand the phenomenon. Stock image 

It’s thought that facial masculinity may be tied to perception of the male monkey’s overall strength and success in competition. But, more research is needed to better understand the phenomenon. Stock image 

MONKEYS SEE FACES IN INANIMATE OBJECTS TOO 

The human tendency to recognizes faces in inanimate objects is called pareidolia - and has been studied extensively in humans.

But researchers were curious to find out if pareidolia also happens in animals.

So, a team at the US National Institute of Mental Health conducted a study, published in the journal Current Biology, involving experiments where monkeys looked at photographs and what they learned from them.

The research team worked with five rhesus monkeys, showing them pairs of pictures on a computer screen while timing how long they looked at them.

Previous research has shown that rhesus monkeys, like humans, tend to stare longer at faces than at other objects.

Researchers showed rhesus monkeys pairs of pictures on a computer screen while timing how long they looked at them. Pictured are examples of the three types of photos used in the study (from left to right: unfamiliar female monkeys,face-like objects, and non-face objects)

Researchers showed rhesus monkeys pairs of pictures on a computer screen while timing how long they looked at them. Pictured are examples of the three types of photos used in the study, including face-like objects, and non-face objects

The monkeys were shown pictures of objects that a group of people had already said had face-like characteristics.

For comparison, the monkeys were also shown pictures of the faces of other rhesus monkeys, and objects that didn't have face-like characteristics.

The researchers found that the monkeys did stare at the images with face-like characteristics for longer than similar objects without these characteristics.

This was the case regardless of the male monkey’s age or facial colour, and any familiarity between the female and the test subject, the researchers note in the study.

While further study will be necessary to pinpoint the reason behind the females’ biases in visual attention, the study suggests it may be linked to their perception of mating and reproductive success.

‘It is possible that variation in facial masculinity has no reliable connection to underlying physiological, behavioural, or genetic factors in male rhesus macaques, in which case there may be no fitness repercussions of female attention to such variation,’ the researchers wrote.

‘However, as male facial masculinity is related to hormone levels and behaviour in humans and other primates, it seems likely that females’ ability to discriminate subtle variation in this trait is the result of evolutionary processes.’