London, Jun 12 (IANS): Researchers have found that hormone oxytocin helps soldiers feel unity among themselves and at the same time aggression towards enemies.

The finding revealed that effect resolves around the hormone oxytocin which is released during stress and when people socialise with each other, reports dailymail.co.uk.

The research which was conducted using a computer simulation game found that volunteers given a spray of the hormone bonded more quickly and deeply with their own group but became much more hostile to outsiders.

Researchers performed three experiments, all on male volunteers, they compared the choices of individuals who received a dose of oxytocin via nasal spray with those who received a placebo.

The volunteers were assigned to three-person groups and introduced to a game in which they made confidential decisions that had financial consequences for themselves, their fellow group members and the competing groups.

The results indicated that oxytocin drives a "tend and defend" response, promoting in-group trust and cooperation while aggression towards competing out-groups.

"Oxytocin is a double edged sword. It makes you kinder to your group but more aggressive to those outside," said Carsten De Dreu, of the University of Amsterdam.

Dreu thinks that the production of oxytocin, which increases at times of stress and in new mothers, has evolved since hunting age when food was scarce and groups had to compete to survive.

"Being aggressive to threatening out-groups makes you a hero, loyal and a patriot to your own group," he added.

Holly Arrow, an expert in the psychology of war at the University of Oregon, said: "Oxytocin is perhaps an important pathway that bonds men together and makes them ready to defend the group".

The hormone appears to have this effect regardless of how naturally cooperative people are.