The Warrior Gene

March 14, 2018

Recently there has been a good deal of coverage in the popular media of the so-called “warrior gene”, presumable a variant of the gene coding for the enzyme monamine oxidase, which metabolizes neurotransmitters.  This allele codes for lower levels of the enzyme, the result being that individuals carrying this allele will accumulate higher levels of neurotransmitters, including noradrenaline and dopamine.  Such individuals have been reported to display aggressive and violent behavior.  Both humans and mice with low MAO-A are reported to more impulsive and aggressive than control groups with the normal alleles.  Persons with high levels of the enzyme display a higher incidence of major depressive disorders.

It important to recognize that this not a gene but rather a modified form (allele) of the gene, that presumable causes individuals to behave in a more aggressive manner than matched controls who carry the normal (“wild type”) gene sequence.

In the last century or more there have been claims, over and over again, of a single gene variant that controls a complex phenotype, such as a gene for homosexual behavior. And over and over again, these claims have failed to be substantiated. Complex behavioral patterns are by definition complex, and are influenced by the rest of the genome, as well as environmental inputs. These meld together to produce the expression of the phenotype. It is easy to imagine situations in which an individual with a propensity for violence will live in an environment in which there is no opportunity to act out his or her aggressive impulses.

We still remain a long ways from a thorough understanding of how the genome and the environment interact to produce their final product.  

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