A group of laboratory monkeys startled scientists when they adopted distinctly human patterns of drinking and chose to consume alcohol in the evenings and at weekends, writes Steve Farrar.
Dee Higley and colleagues at the National Institute on Alcohol Abuse and Alcoholism in the US have been investigating the influence of stress on drinking.
They studied a captive social group of 11 young adult rhesus monkeys that were given continuous 24-hour free access to an ethanol-aspartame solution over a 12-week period. They could choose water as an alternative.
Each animal wore a microchipped collar that enabled the computer-controlled drink dispenser to log the alcohol intake of individual monkeys.
The scientists were hoping to identify a few animals that were essentially addicted to alcohol. Such a model would help research aimed at understanding and combating human alcoholism.
But, as revealed at the 25th meeting of the American Society of Primatologists, the monkeys had a surprise in store for the scientists.
"Instead of drinking day in day out as we'd expected they would, the monkeys developed a set pattern of increased consumption in the evenings and at weekends," Dr Higley said.
"They were basically drinking when we had gone home, when they felt relatively safe."
Dr Higley said that a number of animal studies showed that stress did increase overall consumption of alcohol.
However, the new research painted a more refined picture. When people were around, the monkeys perceived a threat and tended not to drink.
It seemed that they drank only once the stress had subsided - when the laboratory staff went home in the evenings and at weekends.
Dr Higley said this pattern fitted in with human experience in which a stressful day at the office tends to lead to an evening session rather than surreptitious swigs at the desk.