Warrior gene

A version of the primate monoamine oxidase-A gene has been referred to as the warrior gene, initially in monkeys then in humans. Several different versions of the gene are found in different individuals, although a functional gene is present in most humans (except in a few individuals with Brunner syndrome). There is not an additional warrior gene, rather the genotype associated with behavioural traits is shorter (30 bases) and may produce less MAO-A enzyme. The variation in this case is actually in a regulatory promoter region about 1000 bases from the start of the region that encodes the MAO-A enzyme. However, research studies emphasise that behaviour is dependent on both genes and the environment.

In 2006, a New Zealand researcher, Dr Rod Lea said that this variant (or genotype) of monoamine oxidase-A was over-represented in a small sample of current Māori. This supported earlier studies that there are different proportions of variants in different ethnic groups. This is the case for many genetic variants, with 33% White/Non-Hispanic, 61% Asian/Pacific Islanders having the shorter promoter variant of the MAO-A gene. This was subsequently discussed in a number of articles in the New Zealand Medical Journal.

The reported suggestion that a single 'gene', in this case a variant of the MAO-A gene, is a significant factor in behaviour has been widely repudiated.