Are you a good judge of character?What about after mere seconds of seeing a stranger—should you still go with your gut?A recent study out of U.C. Berkeley suggests it wouldn’t be a crazy idea. Subjects were astoundingly accurate at judging how kind, compassionate and trustworthy strangers were—after watching them for just 20 seconds. That may seem like a green light to go with your split-second instincts on your next blind date, but lead author Aleksandr Kogan, Ph.D., cautions it’s far from a no-fail method.

READ MORE: First Impressions On Speed Dates

“These are not very reliable judgments we are talking about; they will be accurate sometimes and highly inaccurate at other times. But on the whole, people are slightly more often accurate than inaccurate,” Dr. Kogan says.Still beats a Magic 8 ball.

Here’s the nitty gritty of the study: First, researchers videotaped couples discussing “times that they suffered” (which tends to be an emotion-eliciting convo). During the discussion, one member of the couple was talking and the other was listening.

Next, subjects who did not know the couples in the videos watched 20-second clips then rated each listener’s kindness, compassion and trustworthiness. To asses these characteristics, the raters relied on body language (think: eye contact, smiles, open body posture, head nods). Again, only the silent partner (the listener) was evaluated.And the findings? The listeners rated as empathetic displayed more of these “trustworthy behaviors,” and were in fact more empathetic…down to their DNA!

READ MORE: The Dark Side of Oxytocin

The listeners with the highest empathy ratings actually had a variation of the oxytocin receptor gene (two “G version” alleles) that predisposed them to these caring behaviors. Oxytocin is known as the “cuddle” hormone released into the brain and blood, thought to foster the warm ‘n’ fuzzy feeling that comes with social bonding and love. Previous research has shown that people with the GG genotype are genuinely more empathic.

Before you think you could see through people down to the core of their being, keep in mind that your first impressions may be swayed by other factors. When people first meet you they may put on a friendlier persona than usual, all because they’re actively trying to make a good impression.

“One of the key differences between observing a rock and observing a human being is that the rock doesn’t know you are watching it and won’t put on a facade to try to be something it may not be. A human can absolutely do this,” Dr. Kogan said.

Another study showed that people form first impressions from as short as a one-tenth-of-a-second glimpse of a photo. Not only that, their impression remains consistent over time and the longer they look at the photo, the more their confidence in that judgment increases. This tendency to judge others’ personalities from a cursory glance suggests that we’ve evolved a cognitive processing system to quickly assess which people to befriend, as a way to help us survive. Could this explain our “sixth sense” when judging an empathic listener?

“In my estimation, we are very far away from having a good enough understanding of genetics and brain functionality to really have a good feel for what evolution could or could not select for,” Dr. Kogan says.Regardless of the reason, your gut instinct about a stranger’s personality may be more dead-on than they’d like you to believe.

Remember that next time you feel shallow for judging someone’s look and body language!

READ MORE: When Body Language Backfires