A baby's cries are tuned to trigger a uniquely fast response from adults, research has shown.
Scientists compared volunteers' reaction times while listening to babies crying, the sounds of adults in distress, and birdsong.
All the sounds were similar in pitch and variability, but response time scores were higher both for men and women when participants heard the sound of infant crying.
"Few sounds provoke a visceral reaction quite like the cry of a baby," said study leader Professor Morten Kringelbach, from Oxford University. "For example, it is almost impossible to ignore crying babies on planes and the discomfort it arouses, despite all the other noises and distractions around.
"It has been clear that babies motivate adults to respond, and that hearing a baby cry must do something. For the first time, we have been able to show a real measurable benefit: we become better at time-pressured tasks."
The research involved a version of the arcade game Whack-a-Mole in which participants had to hit one of nine buttons, reacting as quickly as possible to whatever buttons lit up at random.
Baby cries were found to elicit faster and more accurate movements in the game.
The findings have been published in the journal Acta Paediatrica.
Previous studies have shown that the sound of crying babies prompts a physiological response in adults which increases heart rate, raises blood pressure and strengthens hand grip.
The new results suggest this is part of a "high alert" state which primes adults to react rapidly to a baby in distress.
"Evolution has decided that it is a good thing for us to look after our young, and there is something in the acoustic properties of babies' cries that evokes a very basic response that appears to be hardwired in ancient parts of our brains," the professor said.
"This is not just of academic interest. Our work is showing that in mothers with postnatal depression, through no fault of their own, this response may be disrupted to some extent.
"Depression and postnatal depression may result in some people not attending so much to babies' cries. We are looking at whether interventions can make a difference to this."