Think you know why you do what you do? Hah! Get a grip! Your reptilian brain is in charge.

In this fascinating look underneath the hood, Shankar Vedantam, familiar to Washington Post readers for his admirable “Department of Human Behavior” column, explains how the brain relegates repetitive information to run in the background. These unconscious biases dictate thoughts and actions to your conscious brain, and the results are startling.


  • Racism, sexism, and many other biases are baked into us from a surprisingly young age. In multiple studies across North America, preschoolers associated positive characteristics with white faces and negative words with black faces, even when their parents and teachers had gone to lengths to ensure they were not taught racist attitudes.
  • Overweight job applicants are widely perceived to be less intelligent and lazier than identically qualified people of normal weight.
  • Gender biases are harder to pin down, because women tend to blame themselves for any lack of success while men don’t notice the cultural currents that sweep them forward and attribute their success to their own efforts and talents. Transgender people are uniquely positioned to report out on the view from both sides, and they confirm that it’s a lot easier to be male.
  • These associations come from the brain’s built-in association programing, a reflex to draw rapid conclusions about the environment the individual must survive in. In a highly social species like humans, our environment is our culture. From the moment we are born we absorb the negative and positive associations our culture presents to us. We file them under “critical background info” and don’t think of them again.
  • You have these biases too, whatever your race, education, or personal beliefs. Don’t believe it? Take the Implicit Association Test at

Take away

We evolved in an environment where having automatic, implicit associations that said “Big rustling thing in bushes: Danger!” could mean the difference between being eaten by a lion or escaping. But our brain’s facility at making and holding associations is not well-suited to our modern pluralistic world and can cause us to act in ways that are contrary to our personal convictions. When our guard is down due to fatigue or fear, we reflexively lock our car door at the sight of a black man (even a Harvard-educated one), or mentally classify Michael Chang as a foreigner and Hugh Grant as an American. These powerful undercurrents cannot be countered by rational arguments to a conscious mind that is unaware they even exist.