The need to develop social skills helped shape the modern human face, scientists have suggested.
Writing in the journal Nature Ecology and Evolution, an international team proposes that our faces evolved not just because of factors such as diet and climate, but also to provide more opportunities for gesture and non-verbal communication.
“We can now use our faces to signal more than 20 different categories of emotion via the contraction or relaxation of muscles”, says Paul O’Higgins, from the University of York in the UK.
“It’s unlikely that our early human ancestors had the same facial dexterity as the overall shape of the face and the positions of the muscles were different.”
The researchers traced changes in the evolution of the face from the early African hominins to the appearance of modern human anatomy and conclude that they are the result of a combination of biomechanical, physiological and social influences.
Human faces are more slender that those of other hominins, and they have a smoother forehead with more visible, hairy eyebrows capable of a greater range of movement. This allows us to express a wide range of subtle emotions, including recognition and sympathy.
And the changes haven’t stopped.
The human face has been partly shaped by the mechanical demands of feeding and over the past 100,000 years they have been getting smaller as our developing ability to cook and process food led to a reduced need for chewing, the researchers say.
This facial shrinking process has become particularly marked since the agricultural revolution, as we switched from being hunter gatherers to agriculturalists and then to living in cities – lifestyles that led to increasingly pre-processed foods and less physical effort.
“Softer modern diets and industrialised societies may mean that the human face continues to decrease in size”, O’Higgins says. “There are limits on how much the human face can change…for example breathing requires a sufficiently large nasal cavity.
“However, within these limits, the evolution of the human face is likely to continue as long as our species survives, migrates and encounters new environmental, social and cultural conditions.”
Related reading: The evolution of the mammal brain