London : The "macho" gene which makes men behave more aggressively than women under stress has been discovered. They say this one gene could explain why men have a "fight or flight" response while women are more likely to try and defuse the situation, the Daily Mail said Thursday. Australian researchers have studied the chemicals secreted by men when they react to stress - and how this influences their behaviour. And they propose that the SRY gene - only found on the Y chromosome - and the proteins it activates in the body are the key. This gene was previously thought just to be involved in the development of male characteristics in the womb. But Joohyung Lee and Vincent Harley from Prince Henry's Institute in Melbourne have shown these proteins are actually present in the brain and other organs of adult males. They have shown these may regulate stress hormones and blood pressure which cause stressed-out men to experience their pulse quickening and adrenaline coursing through their veins - triggering aggression, the newspaper added