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Can you tell at first glance if someone is likely to be a good partner or parent? New research suggests that observers can identify the most nurturing and socially sensitive people, just by watching their behavior for 20 seconds — and that these highly empathetic people are more likely to have a gene variation associated with trust and caring.

The genetic variation affects the receptor for oxytocin, often referred to as the “love hormone” or “cuddle chemical” because it plays a role in social bonding, trust, empathy and generosity. Levels of oxytocin increase during orgasm and childbirth, and it helps the formation of bonds between friends, lovers, and parents and children.

Research has shown that people with two G variants of the gene are more empathetic and “prosocial,” showing more compassion, cooperation and positive emotion. In contrast, those with the at least one A version of the gene tend to be less empathetic, may have worse mental health and are more likely to be autistic.

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In the new study, researchers videotaped 23 romantic couples while one person listened to his or her significant other describe a time of personal suffering. Then, 116 strangers were asked to watch silent 20-second clips of the videos and rate the listeners on how supportive and trustworthy they seemed.

People who were rated as most empathetic based on their body language and behavior — things like keeping eye contact, smiling and nodding while their partner spoke, and having open body posture — were also more likely to have the GG genotype, researchers found. Of the 10 people rated the most trustworthy, six had the GG variant; of the 10 rated lowest on trust, nine had two copies of the A gene variation.

“We were floored by how strongly significant the results were by genotype for such a small number of people evaluated,” says Sarina Rodrigues Saturn, assistant professor of psychology at Oregon State University and an author of the study.

Men who carried the GG genotype were also more easily identified as being sensitive, compared with the women.

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But Rodrigues Saturn warns against seeing the GG genotype as the determining factor in a person’s ability to empathize or connect. “I would definitely caution everyone not to think of this as an ’empathy gene.’ There are many environmental, cultural and genetic influences that interplay with each other to make up the entire person,” she says. “Neurochemical genetic variations can influence emotional states and traits but they definitely don’t determine who becomes what. … Our biological makeup only accounts for less than half of our traits, and this one genetic variation interacts with many other genes, experiences, societal structure, etc.”

Indeed, one study found that while Americans with the GG genotype are more likely to seek emotional support from friends, people with the same genotype in Korea, where such help-seeking is considered burdensome, are less likely to do so.

What’s more, the actions of oxytocin are complex. Although the hormone is widely recognized for boosting feelings of trust and caring, some studies suggest that how people were raised influences whether the hormone actually encourages social connection. For example, when men whose mothers were not particularly nurturing are given doses of oxytocin, they tend to recall more bad memories of mom, compared with men who felt more cared for as children; they find themselves thinking more fond thoughts of mom under the hormone’s influence.

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The new study has received some strong criticism from geneticists online for its small scale. Wrote Discover’s Ed Yong in his covered the findings:

Daniel MacArthur, who blogs at Genetic Future, said, “[A sample size of] 23 for genetics means the paper might as well not exist. It carries no useful info. Without a larger sample and independent replication, it’s safest to simply assume these results are false.” Joe Pickrell from Harvard Medical School, agreed: “If the sample size is 23… there’s no way that’s a real association.”

Lead author Aleksandr Kogan, a postdoc at the University of Toronto, responded that he would normally agree with such a critique, except for two facts. The first is that the number of observers and video clips observed actually makes for a larger sample size, providing greater statistical power.

Secondly, he says, he believes there is more validity to the finding because “fortunately, there have been about a dozen studies conducted in the past 10 years looking at [this gene] and self-reported empathy, and the findings have been all consistent — and used hundreds of participants.” He adds, “I would strongly agree that outside replication is still very necessary and that this is really just a preliminary finding.”

Although we tend to think of humans as being primarily selfish by nature — at least in American culture — a growing body of research suggests that our genes, despite some variations, generally incline us toward collaboration and connection in most situations. Further research in this area might help us discover how to bolster these altruistic tendencies and understand the environments that are most likely to encourage them.

The study was published in the Proceedings of the National Academy of Sciences.

Maia Szalavitz is a health writer at TIME.com. Find her on Twitter at @maiasz. You can also continue the discussion on TIME Healthland’s Facebook page and on Twitter at @TIMEHealthland.