A study on the history of facial expressions has discovered humans developed friendly facial expressions to attract less-aggressive, selected breeding partners, as a result of ‘self-domestication’. The new study on the ancient human smile was published this week in Science Advances . The study was conducted by Matteo Zanella and a team of researchers at the University of Milan. They have discovered that the kindness humans convey through facial expressions is a key factor in human evolution.

A series of gene mutations found present in genetic samples from Neanderthals suggests these mutations may have caused humans to “self-select less aggressive mating partners” leading to ‘self-domestication’. The term ‘ self-domestication’, is used scientifically to describe the reproductive patterns and behaviors observed in wild animals that led to evolutionary shifts without humans intervening to force selective breeding practices. It was this that has led to the domestication of dogs, cats, and according to a Daily Mail report, even bonobos.

Evolving the Cuddly Look

Comparing genetic data gathered from human stem cells from the remains of two Neanderthals and one Denisovan, the University of Milan researchers suggest our friendly and welcoming facial expressions were an important factor in human evolution leading to “Williams-Beuren syndrome.” This syndrome causes the distinctly wide mouth and small nose that we perceive as a kind and welcoming impression, a sort of - “I am not going to kill you today” kind of look.

A Neanderthal model from the Britain One Million Years of the Human Story exhibition ( National History Museum )

The specific genes being studied are known to science as ‘BAZ1B’, which the researchers say is a ‘master regulator’ that influences human facial expressions, and it was this specific gene that was responsible for dogs having two extra muscles by which they can narrow and widen their eyes in a range of expressive ways, which wolves are unable to do.

A report about the new study in Science Advances says that in 2014 three scientists proposed that as people selected animals for their perceived tameness, they also selected for genetic changes that slightly hamper movement of some developmentally important cells. These cells, known as crest cells, are present early in embryonic development and migrate to different parts of the embryo shaping bones and cartilage in the face, smoothing muscles, adjusting adrenal glands, altering pigment cells and regions of the central nervous system. These researchers’ found that the “mild genetic changes” that produce crest cells and don’t move as well, led to domesticated animals having the “cuddly look”.

Genetically Boosting Our Social Lives

The University of Milan researchers found that the mutations they observed in the BAZ1B gene, which is linked to the parts of the brain that control facial expression, were ‘absent’ in the Neanderthal and Denisovan samples. This they believe, helped humans along the evolutionary path by pushing us to select mates with kind, friendly, “I probably won’t kill you” facial expressions. It is thought that selective mating practices among some Neanderthals that led to the mutation of the BAZ1B gene. This in turn, probably contributed to the evolutionary twist that saw Homo sapiens develop their distinctively expressive faces.

Comparison of Modern Human and Neanderthal skulls from the Cleveland Museum of Natural History. ( DrMikeBaxter / CC BY SA 2.0 )

While it has long been suspected by genetic scientists that humans developed smiles to enhance mating options, in an interview with Newsweek, Matteo Zanella, said the study was the ‘first empirical validation of the self-domestication hypothesis.’ And his team suspect facial changes in humans were “part of a process of reduction in reactive aggression” by which they boosted their “pro-social, cooperative profile.”

Backing this all up, University of York lecturer Penny Spikins who was not involved in the study, told Newsweek that it’s “all too easy” to interpret human evolution against individualistic success, but she says these new findings illustrate how critical interpersonal social processes were in making us human. According to the scientist, this is an important step in “clarifying the relationship between the evolution of the human brain and the evolution of the species,” which demonstrates how important “emotional and social sensitivity” is to human beings.

The Human Smile Reassures Strangers

In the real world, we all apply these genetic mutations every time we meet someone for the first time, and most of us form an opinion about someone based on whether they smile, or not. An article on A Conscious Rethink says smiling is a universal sign of friendliness, and wearing one makes you immediately more approachable and we experience this when we are searching for someone to help with something. For example, would you approach a person scowling or smiling?

Modern day humans smiling, from different origins ( olly / Adobe Stock)

And now we know a warm and inviting human smile goes back a long way, to a time when smiles welcomed strangers and helped build trust in a world before words were used. We also know that our desire for more matched mates, selected lovers, took over the “just mate and get on with it because that is what you are here to do” attitude.

Top image: Depiction of an ancient human smile Source: procy_ab / Adobe Stock

By Ashley Cowie