A macaque monkey on Cayo Santiago, Puerto Rico. Credit: Jamie Whitehouse
Sept. 11, 2017 (Phys.org) -- Scratching is more than an itch -- when it is sparked by stress, it appears to reduce aggression from others and lessen the chance of conflict.
Scratching can be a sign of stress in many primates, including humans.
Research by Jamie Whitehouse from the University of Portsmouth is the first to suggest that these stress behaviours can be responded to by others, and that they might have evolved as a communication tool to help social cohesion.
The research, published in Scientific Reports, raises the question whether human scratching and similar self-directed stress behaviours serve a similar function.
Jamie said: "Observable stress behaviours could have evolved as a way of reducing aggression in socially complex species of primates. Showing others you are stressed could benefit both the scratcher and those watching, because both parties can then avoid conflict."
The research team conducted behavioural observations of 45 rhesus macaques from a group of 200, on the 35-acre island of Cayo Santiago, Puerto Rico. The team monitored the naturally occurring social interactions between these animals over a period of eight months.
The researchers found that scratching in the monkeys was more likely to occur in times of heightened stress, such as being close to high-ranking individuals or to non-friends.