The brains of parents - especially mothers - appear to be wired up to respond to the cries of babies.
Cries are a sign of distress
A team from the University of Basel used sophisticated scans to measure brain responses to recordings of babies' cries and laughter.
One measure showed the cries provoked a stronger reaction in parents than in childless people, and another showed a stronger response in women than men.
The research is published in the journal Biological Psychiatry.
The scientists found that a baby's sobs triggered increased activity in a particular area of the brains of parents of both sexes.
This area, called the amygdala, plays a central role in processing emotions.
However, measures of activity in the amygdalas of childless adults, both men and women, showed they were more likely to be stimulated when a baby laughed, rather than cried.
Lead researcher Professor Erich Seifritz, of the University's Department of Psychiatry, told BBC News Online that the findings made biological sense.
He said: "For a parent a baby's cries are much more important than for a non-parent.
"A parent needs to foster their offspring, so that they spread their genes into the world.
"So it is important that they have mechanisms in their brain to make sure they are sensitive to needs of their baby.
"In evolutionary terms, this means that a child is more likely to survive and pass on his or her genes."
However, the research came up with different findings when it focused on a second area of the brain called the prefrontal cortex. This is a complex structure, which is not fully understood, but is also thought to play a role in processing emotion.
These readings showed that all women, regardless of whether they had children of their own, registered altered activity in this area in response to a baby's cries.
However, men, again regardless of their parental status, showed no sign of raised activity in this region.
The researchers believe that a baby's cries may trigger a noise filter in the prefrontal cortex which enables a woman to focus solely on a child's cries, to exclusion of other sounds.
In turn, this may stimulate the transmission of electrical impulses to other brain areas, triggering strong emotions, and caring behaviour such as feeding or cuddling.
Professor Seifritz said the findings suggested that women's prefrontal responses might be hard-wired, whereas for men and women their amygdala response was more modulated by experience.
However, he said the more work was required to explain the possible interaction between the amygdala and the prefrontal cortex.
The researchers hope their work will provide new clues about how people relate to each other socially, and about what goes wrong when people develop emotional disorders, such as Borderline Personality or Mood Disorders.