Single men have higher levels of testosterone than men who are married with children, scientists have discovered.

Researchers at Harvard University said the differences may be linked to men's daily social interaction experiences.

They suggested that constant interaction with family members reduced the hormone in married men and encouraged them to be faithful.

Fathers seem to show an even more dramatic difference from unmarried men

Peter Gray, Harvard University

In the case of single men, they suggested that high hormone levels caused by a lack of interaction with spouses or children encouraged them to seek out new partners.

The findings, detailed in New Scientist magazine, back up previous studies which have shown that increasing testosterone levels can cause men to play the field.

Hormone tests

Anthropologists Peter Gray and colleagues measured testosterone in the saliva of 58 men who were either single, married or married with children.

They found that hormone levels in all of the men fell over the course of the day in line with the natural cycle.

However, while the decrease was most obvious in married men than in bachelors it was even more pronounced in married men with children.

Dr Gray stated: "Fathers seem to show an even more dramatic difference from unmarried men."

The authors of the study, which was originally published in the journal Evolution and Human Behavior, said the differences may be explained by differences in social contact.

They said being around wives and children could cause a man's testosterone levels to fall.

Similarly, this lack of contact may cause hormone levels in single men to rise.

They added that low rates of testosterone may encourage men to stay at home and embrace their role as family men.

Further study

The Harvard University scientists are hoping to expand their theory further by examining the differences between married men and those who are married with children.

They will compare hormone levels in married men with children with those who are separated but have joint custody of their children.

They hope to discover whether marriage or having children is key to reducing testosterone.

Benjamin Campbell of Boston University said the findings echoed some recent studies.

He said that while they had shown that winning or losing in sport affect the hormone maybe parenting had a similar affect.