A New Zealand researcher claims there is an over-representation of the "warrior" gene, which has been linked to aggressive behaviour, in Maori men.

Dr Rod Lea said the monoamine oxidase gene, carried by a large number of Maori, could be key to addressing health issues.

The genetic epidemiologist at the Institute of Environmental Science and Research in Wellington said the gene has been linked to aggressive behaviour as well as addictions to things such as tobacco.

Maori leaders said there were many other factors which dictated whether people turned violent, such as poverty.

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The gene was discovered by American researchers but had not previously been linked to an ethnic group.

Dr Lea, who has been speaking at an international conference in Brisbane, denies Australian reports that quoted him suggesting the gene has links to criminality.

Australian Associated Press quoted him as saying: "It is controversial because it has implications suggesting links with criminality among Maori people. I think there is a link, it definitely predisposes people to be more likely to be criminals and engage in that type of behaviour as they grow older.

"There are lots of lifestyle, upbringing-related exposures that could be relevant here so, obviously, the gene won't automatically make you a criminal."

He said Maori were also more prone to obesity than white New Zealanders, and while the researchers don't yet know the role of lifestyle factors, they believe ancestral genetics played a vital role.

Small influence

Dr Lea said today he believed the influence of the gene, which appeared to feature in about 60 per cent of Maori men compared with 30 per cent of European men, could be small.

"I believe this gene has an influence on behaviour of humans in general, but I also believe that the influence is rather small," he said on National Radio.

"We have to be clear that behavioural traits such as susceptibility to addiction, aggressive behaviour, risk taking, all those sort of things are extremely complex and they are due to numerous factors including non-genetic environmental factors like upbringing and other lifestyle factors.

"So there is an influence there, but it's probably a minor one in the scheme of things."

His group is now collecting thousands of DNA samples from Maori to investigate these traits. They can then work out exactly what role each gene plays and use this to explore these trends in the mainstream populations.

Maori MP Hone Harawira said he had been hearing similar things for decades.

"I remember 30 or 40 years ago when I was a kid people said Maori had a natural inclination to play the guitar, that Maori had a natural inclination to play rugby, Maori were good on bulldozers etc...," he said. "I've stopped listening to all that sort of carry on."

However if the theory could be backed up with solid evidence then it might be worth a closer look.

Mr Harawira said the main factors contributing to Maori violence were high unemployment rates, poor health, lower life expectancy poor educational achievement and in many cases severe poverty.

Maori Party co-leader Tariana Turia dismissed the research as incredible.

She told The Press newspaper she had heard of Maori having a genetic pre-disposition towards alcoholism, but it was a big leap to include violent tendencies in that.

"I realise that violence is an issue to us, but there are very common factors as well with violence which are not really related to race," she said.

National Urban Maori Authority chief executive John Tamihere said he was keeping an open mind.