As a student of human nature, I often wonder why anyone goes on family holidays. I pondered the matter again recently, when we took the kids to southern Italy. Naturally, it rained almost solidly every day. There were moments familiar to any parent, like the deflating sound of an exhausted child waking up at 6.20am; the attempt to explain Pompeii to a three-year-old; or the evening we walked forever to the restaurant we’d read about, ordered food, and then watched the children fall asleep at table before the meal arrived. Yet by the time easyJet landed us home, I think I’d figured out why people take family holidays – and, by extension, why they have families.

The “challenges” of family holidays are well-known. It’s hard enough getting on with your spouse and kids at home, let alone when cooped up with them for days. Susan M. Shaw, expert on leisure at the University of Waterloo in Canada, thinks the term “family leisure” is problematic. “Research suggests that such activities do not always live up to the leisure ideal,” she writes, darkly. Brian Viner in his Cream Teas, Traffic Jams and Sunburn: The Great British Holiday describes one seaside holiday when he shared a bedroom with his parents, it rained all week, he cut off clumps of his hair from boredom, his mother smacked him and then, as a finale, they heard on the car radio on the drive home that Robert Kennedy had been shot dead.

Family holidays probably don’t add much to the sum of human happiness. However, as an economist friend of mine likes to argue, people don’t have children for happiness. It’s a cliché of happiness research that parents are less happy than childless people. Rather, says my friend, having children is best understood as a biological urge. You have them not for the present but for the future, to perpetuate your genes when you are gone. And likewise, you go on family holidays not for the present but for the future.