Unlike women, men don't curb certain risk-taking behaviours when a baby is present, a new psychology study at the University of Warwick suggests.
Whereas women are significantly more cautious when they are partnered with small children in a gambling game measuring their attitude to risk, men don't substantially alter their willingness to take a chance.
Researchers suggested this could be due to evolutionary forces that select for men who are more competitive and risk-seeking in order to establish status and women who are more risk-averse in order to protect their offspring.
Scientists at the University of Warwick and the University of Basel observed students playing a gambling game while alone and while paired with either an image of an attractive man, woman or baby with whom they imagined they would share their winnings.
A second less surprising finding of the study was that men took more risks when partnered with other men – consistent with theories suggesting that men are driven to compete with other men in order to maximise their reproductive opportunities.
However men did not increase their risk-taking behaviour when paired with a woman, a fact researchers believed was down to the co-operative design of the game where participants shared their winnings with their partner.
This particular finding has parallels in the real world where studies have shown that men in committed relationships show less risky behaviour as they no longer need to compete with other males to gain a woman's attention.
Dr Thomas Hills of the Department of Psychology at the University of Warwick said: "To our knowledge this is the first study to look directly at the effect of babies on male and female risk-taking.
"Our attitudes to risk form a big part of our personality and determine our behaviour in all sorts of areas – for example how we approach financial investments or what leisure activities we indulge in.
"Even though the women in the study were not the mothers of the babies they paired with, just having a baby involved in the game was enough to substantially change their behaviour.
"It's as if babies turn off women's a willingness to take a risk – but interestingly the same doesn't apply to men."
The study The baby effect and young male syndrome: social influences on co-operative risk-taking in women and men was published in the journal Evolution and Human Behavior.
Eighty undergraduate students (40 male and 40 female) took part in the study.
The participants accumulated cash while pumping up a computer-simulated balloon which could explode randomly at any moment.
As the game progressed, participants had to decide whether to stop pumping and "bank" the winnings – or whether to continue and risk the balloon exploding and all the cash being lost.