A small group of neurons in the brains of mice may control whether males are aggressive or submissive in encounters with other males, according to new research.

Why it matters: Social dominance exhibited by certain males in groups — the basic definition of alpha males — is an important evolutionary trait in nearly every animal species (including, to a limited extent, humans). Male "winners" in aggressive contests or situations with peers accrue benefits, provided they keep winning.

Scientists have known for some time that a part of the brain (the dorsomedial pre-frontal cortex) is involved in regulating social dominance traits in males. What they didn't know was how it worked. In this new study, scientists tested the mechanism by pitting mice against each other, and then activating the neurons (or shutting them down) during those "showdowns" to see how they reacted.

What they found: Mice with the fired-up neurons in that part of the brain acted more like alpha males (pushing back, fighting, resisting, etc.), while those that had those neurons suppressed were more passive and less inclined toward social dominance behavior that characterizes "winning."