The faces we pull when we are happy, sad or angry may be passed from generation to generation, according to researchers.
An Israeli team discovered facial expressions among family members bore striking similarities.
Writing in the Proceedings of the National Academy of Sciences, they said their findings suggested expressions may be hereditary.
This confirms an idea posed by Charles Darwin in 1872.
In his famous work, The Expression of the Emotions in Man and Animals, he suggested facial expressions were innate.
To test this, University of Haifa researchers analysed the facial expressions of 21 volunteers who had been blind from birth along with those of their relatives.
They interviewed the participants, asking them to recount experiences of when they were happy, sad, angry and disgusted, and recorded their mannerisms while doing so.
They also set them a test to see what they looked like when they were concentrating, and shocked them to witness their expressions of surprise.
When the researchers compared the results, they discovered that even though the blind volunteers had never seen their relatives' faces before, their facial expressions were extremely alike.
The strongest correlation was for the negative emotions.
Lead researcher Gili Peleg, from the Institute of Evolution at the University of Haifa, said: "We have found that facial expressions are typical to families - a kind of facial expression 'signature'."
She said her results suggested that facial expressions were inherited and therefore had an evolutionary basis.
"Our next step is to find the exact genes that influence facial expression."
This, she added, could have an impact on autism research, where facial expressions are central to the disorder.
Professor Ruth Mace, an evolutionary anthropologist from University College London, UK, said: "We have known that expressing your emotions is something that has been moulded by natural selection for a long time.
"As a social species, it makes sense for us to be able to read each others' emotions to predict how they are going to behave and how they are going to respond.
"It is all part of being social and living in groups. Being able to read people's faces is very important and it makes sense that there is a hereditary component."