Parenthood and happiness are hard to study. One researcher commented, “If you want to understand the causal effect of sleeping pills on somebody’s sleep, you can run placebo trials, but kids can’t be handed out at random to see what effect they have on people”.

What is certain is that across the developed world people are choosing not to have children, thus rejecting what was once considered an inevitable and essential part of the human experience – procreation. Perhaps that’s not so surprising. Having children can have a significant impact on finances, careers and the planet.

Children in the wealthy West are a huge financial commitment. The average middle-class US family has spent more than $245,340 on each child by the time they’re 18. In the UK, the cost of raising a child has swelled 63 per cent since 2003, with childcare alone eating up 27 per cent of the average salary (Centre for Economics and Business Research in London).

Finances aside, there’s an environmental issue. Children can come with a large environmental footprint. In the US you can recycle and bike to work all you want to reduce your carbon emissions, but those gains will be 20 times less than the CO2 impact of having a child, according to a 2009 study from Oregon State University.

Then there is the planet’s “carrying capacity”. United Nations projects that “if current population and consumption trends continue, humanity will need the equivalent of two Earths to support itself. Some have taken this message to heart.

There is now almost half a century of evidence on the relationship between having children and personal happiness. On the negative side, having children makes couples less happy with their sex lives, is associated with depression, sleep-deprivation, and, as one study puts it, “hastens marital decline”. One oft-cited 2006 study co-authored by Princeton psychologist Daniel Kahneman found that a group of working US mothers ranked childcare 16th out of 19 everyday tasks in terms of positive feeling, just ahead of commuting to and from work, and work itself.

A study of more than 14,000 Australian and German couples, found that mothers reported a sharp rise in stress after the birth of a child – three times that of the father – and that it increased year-on-year until four years after the birth, when the study stopped. Further research that followed more than 2000 first-time German parents, found that the average hit to happiness exacted by the arrival of an infant is greater than a divorce, unemployment or the death of a spouse.

Sonja Lyubomirsky, a psychologist at the University of California, Riverside, published a paper in the journal Psychological Science, showing that having children made men (but not women) happier. Others have pointed out it is marriage itself that makes people, especially men, happier. Child rearing is another matter.

The situation seems to be that people who have kids have all sorts of differences from the people who don’t have kids. There are so many variables: income, the helpfulness of relatives, the way the parents have been brought up (happy or unhappy homes), the age of the parents, (for people younger than 30, children are associated, on average, with a decrease in happiness. From 30 to 39, the average effect on happiness is neutral, and at age 40 and above, it’s positive). Studies show that parents’ happiness increases a year or so before the birth of the first child, and then returns to pre-birth levels by the time the baby is about one.

So the true picture is clearly nuanced. Parenthood can boost people’s satisfaction with their lives, apart from their financial circumstances – but for many the money woes associated with children are so great that any additional happiness they felt was swallowed up. (Adapted from an article in the New Scientist).

I think the truth is incredibly complex, as complex as the character and feelings that we all have as humsn beings – up, down, content, confused, frustrated, elated.