Tortoises are born with a natural preference for faces, according to new research from scientists at Queen Mary University of London, the University of Trento and the Fondazione Museo Civico Rovereto.
The study provides the first evidence of the tendency for solitary animals to approach face-like shapes at the beginning of life, a preference only previously observed in social species such as human babies, chicks and monkeys.
The researchers tested the reactions of hatchlings from five different species of tortoise to different patterned stimuli, made up of a series of blobs. They found that the tortoises consistently moved to areas with the 'face-like' configuration - containing three blobs arranged in an upside-down triangle shape.
The findings suggest that this early behaviour likely evolved in the common ancestors of mammals, reptiles and birds more than 300 million years ago.
Dr Elisabetta Versace, lead author of the study from Queen Mary University of London, said: "Researchers have previously observed this spontaneous attraction to faces in social animals such as humans, monkeys and chicks. Because all these species require parental care, it was thought this early adaptation was important for helping young animals respond to their parents or other members of the same species. However, now we have shown that this behaviour is also found in solitary tortoise hatchlings, suggesting it may have evolved for another reason."
Tortoises were hatched and kept away from any animal or human faces from birth until the start of the test. Each animal was then placed in the middle of a rectangular space divided into four areas containing either a face-like or control stimuli. The researchers analysed the preference of hatchlings for face-like stimuli by recording the first area the animal entered during the experimental period.
Unlike birds and mammals, tortoises are solitary species - they have no post-hatching parental care and do not form social groups as adults. Previous research has even shown that tortoise hatchlings ignore or avoid members of the same species in early life.
Silvia Damini from the University of Trento, said: "It is possible that this preference for face-like stimuli enhances learning from living animals in both social and solitary species from the early stages of life. In fact, other animals can provide information on important environmental factors, such as the availability of resources".
Gionata Stancher, Head of the Tortoise Sanctuary Sperimentarea (Fondazione Museo Civico Rovereto, Italy) where the experiments were conducted, said: "Being able to recognise and respond to cues associated with other living animals could help young animals acquire information vital for their survival."
Notes to editors
* Research publication: 'Early preference for face-like stimuli in solitary species as revealed by tortoise hatchlings' Elisabetta Versace, Silvia Damini, Gionata Stancher, PNAS.
* Supporting images and video available on request.
* For more information or a copy of the paper, please contact:
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Proceedings of the National Academy of Sciences