Children as health insurance.

Children seem to strengthen their parents' immune system:

(New Scientist. July 14, 2012) Parents less likely to catch colds and flu - health

Sheldon Cohen and colleagues at Carnegie Mellon University in Pittsburgh, Pennsylvania, reviewed three studies in which researchers put either a flu virus or a rhinovirus, which causes colds, into people's noses, then tracked who fell ill. Cohen's team found that parents were only 48 per cent as likely to develop an infection as people with no kids.

The more children there were in the family, the more parents were protected against illness. But the kids did not need to be present: parents whose children had already left home were only 27 per cent as likely as the childless adults to get sick (Psychosomatic Medicine, DOI: 10.1097/psy.0b013e31825941ff).

tags: distribution, health, biology