Men may have the ultimate excuse for being prickly under pressure - apparently it's all down to their genes.
Scientists think they have identified the "macho" gene that makes men more aggressive when under stress.
Experts say it could explain why men typically have a "fight or flight" response while women try to defuse difficult situations, or "tend and befriend".
Australian researchers have proposed that the SRY gene - found only on the Y chromosome - and the proteins it activates in the body are to blame, after studying the chemicals secreted by men reacting to stress.
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The gene was previously thought to be involved only in the development of male characteristics in the womb, but Dr Joohyung Lee and Professor Vincent Harley from Prince Henry's Institute in Melbourne have shown that its proteins are present in the brain and other organs of adult males.
They say the gene may regulate certain hormones and blood pressure, causing stressed-out men to feel their pulses quickening and adrenaline levels surging - biological changes that trigger aggression.
By contrast, psychologists believe that women's behaviour is governed by the release of oestrogen and the so-called "cuddle hormone", oxytocin.
Dr Lee said: "The aggressive 'fight or flight' reaction is more dominant in men, while women predominantly adopt a less aggressive tend and befriend response.
"New evidence indicates that the SRY gene exerts 'maleness' by acting directly on the brain and peripheral tissues to regulate movement and blood pressure in males. We propose SRY provides a genetic basis to explain why the 'fight or flight' response is manifested mainly in males rather than females."
Researchers believe the study, published in the journal BioEssays, could lead to new treatments for personality disorders. It may also explain why conditions such as hyperactivity, autism and Parkinson's affect more men than women.
- DAILY MAIL