Led researcher Peter Gray says that the new finding provides a social and evolutionary explanation for the decrease in testosterone, rather than an age-related one.
Ariaal men remain single "warriors" until they are around 30, at which time they marry one or more women.
The researchers measured testosterone in 205 Ariaal men during the course of study. They found that men with one wife had lower levels of the hormone than unmarried men.
It was also found that men with more than one wife had the lowest levels of all.
"Testosterone levels are lower among married men probably because they are investing less in mating effort," the New Scientist quoted Gray as saying.
He made it more clearer to understand by saying that married men had lower levels of testosterone because they no longer had to compete for mates.
The researchers say that the link between mating effort and testosterone is made clearer by the fact that the Ariaal have an "aloof" marital system.
Apart from sex, husbands and wives have very little to do with each other, and men are minimally involved in childcare.
In a separate study of 203 married Ariaal men, only three participants said that their wives were a source of emotional support.