But the scientists have found that this chemical, often referred to as the love or bonding hormone, also makes them – like mothers – incredibly aggressive to outsiders.
Using a computer simulation game they 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.
Dr Carsten De Dreu, of the University of Amsterdam, said that the phenomenon was known as "parochial altruism" or "tend and defend".
This meant that boosted levels of oxytocin produced "in-group love" and "out-group aggression", he said.
TVNL Comment: It has the same effect as religion or nationalism. Don't we have enough hate for "others?"
