Leo Durocher once said that nice guys finish last. While that may be true in baseball, in real life the nicer men tend to get married.

Lying, aggression and criminal behavior are less common in married men than in single men. No one has really been sure whether this happens because of the marriage or whether married men were nicer to begin with.

A study from Michigan State University hints that both are true.

When looking specifically at the identical twins in the study, the married twin engaged in less antisocial behavior after his marriage than the unmarried twin did at that same age. This suggests that marriage itself lowers antisocial behavior.

The study looked at 289 pairs of male twins, over half of whom were identical twins. The twins were followed from age 17 to age 29. None were married at age 17, while 59% were married at age 29. Their personality was assessed for antisocial personality disorder, using standard psychiatric definitions, at age 17, 20, 24 and 29.

The men who eventually married showed fewer antisocial tendencies than those destined to be single, even at the ages of 17 and 20. This suggests that men with more antisocial tendencies are less likely to marry. At age 29, the unmarried men were classed as having 1.3 antisocial behaviors while married men had only 0.8.

Identical twins have identical genes and, being siblings, were usually raised in the same environment. Because of this, they tend to have the same types of antisocial tendencies. When looking specifically at the identical twins in the study, the married twin engaged in less antisocial behavior after his marriage than the unmarried twin did at that same age. This suggests that marriage itself lowers antisocial behavior.

The married men in the study were already nice before they got married and they became even nicer after the marriage.

This suggests that unmarried men with antisocial tendencies will have to clean up their act a bit if they ever want to get married. Of course, it may only mean that they'll have to work a lot harder to find that special someone. Henry VIII, a man of decidedly antisocial behavior, had six wives.

An article detailing the study was published in the December 2010 issue of Archives of General Psychiatry.