When a man decides he wants to spend the rest of his life with a woman and she feels the same way, it is most likely due to a wealth of oxytocin, a hormone a new study suggests is the driving force of monogamy.

According to the Los Angeles Times, researchers from Bonn University Medical Center, in Germany, suggested oxytocin, a hormone from the pituitary gland, is present in monogamous couples. The researchers found that the hormone enhances their attraction to their chosen romantic partner.

For their experiment, the researchers administered oxytocin to a group of men and showed them photos of their significant other as well as an equally attractive stranger. The men did not only verbally express they felt their partner was more attractive, their brain activity confirmed it.

"Monogamy is actually quite costly for humans, so there must be some form of benefit," said study lead researcher Rene Hurlemann, a psychiatrist at Bonn. "We'd expect humans, especially males, would disseminate their genes. That would be a very strong evolutionary force driving male behavior. But what drives males to stay in a monogamous relationship?"

After the administering of the oxytocin, the men's brain activity was most active in areas associated with reward and motivation. The oxytocin release may trigger dopamine, a neurological agent that is mostly associated with reward, motivation and addiction.

During such social and intimate activities as hugging, kissing, massages and sexual intercourse, oxytocin is released. Consequently, oxytocin encourages social behavior, trust and attachment to a significant other.

"When oxytocin strengthens the partner bond, it increases the stability of the persons providing nutrition and thus the chances of survival for the progeny," said Hurlemann in a press release.

The researchers' work is published in the journal Proceedings of the National Academy of Science.

He said the feeling of love and oxytocin is the same type of stimulant people take drugs to feel. The feeling is the brain's reward system. Monogamy has long been a mystery for those who try and study it, but this new explanation would also do well to explain the sorrow that goes along with a break-up.

"This biological mechanism in a couple relationship is very similar to a drug," said Hurlemann. "This could also explain why people fall into depression or deep mourning after a separation from their partner: Due to the lack of oxytocin secretion, the reward system is under-stimulated, and is more or less in a withdrawal state."