An estimated one in five people will suffer with depression in their lifetime . But scientists have now found that Macaque monkeys show similar signs of depression to humans , such as shying away from a group , losing their appetite and adopting a hunched posture . By studying creatures in a social situation , they hope to learn more about why humans may become depressed , which could improve treatment for the debilitating mental disorder . Scientists have found that Macaque monkeys show similar signs of depression to humans , such as shying away from a group ( shown in E ) and adopting a hunched posture ( shown at A , B , D and E ) . Image C suggests bullying from dominant monkeys ( marked in the pictures with red arrows ) in the form of a cut to the monkey 's ear . Intimidating behaviour ( B and D ) may explain the monkeys ' depression . Previous studies have used rodents , which 'do not realistically resemble the etiopathological [ causal ] development of depression , which occurs naturally in a social context , ’ according to the study , published in Nature . Researchers at Chongqing Medical University , China , and Wake Forest University in North Carolina , examined depression in cynomolgus macaque monkeys living in social colonies at Zhongke Experimental Animal Co. in Suzhou , eastern China . The cause of depression in some cases , appears to be down to bullying behaviour by dominant members of the colonies , such as intimidating and even attacking lower status monkeys . Each colony was made up of two males and approximately 20 females as well as their offspring , reflecting how they would live in the wild . Twenty females showing symptoms of depression , such as no interest in food , grooming or mating . Dominant behaviour is marked with red arrows , above and depressed monkeys with blue arrows . Feeding : The depressed monkeys spent less time eating and drinking than their healthy peers . Behaviour : They spent less time resting on elevated perches such as shelves and hanging chains , which are favourites with healthier and more dominant monkeys . Movement : Depressed subjects spent more time sitting on the floor and less time walking around . Grooming : The sad monkeys spent less time grooming each other and being groomed , which is a sign of sociability in healthy monkeys . They also spent less time taking care of themselves , by scratching , for example . Nursing : They also nursed their infants less than healthy monkeys . A total of 52 colonies were observed and 1,007 female monkeys screened for depression , Real Clear Science reported . Twenty females showing symptoms of depression , such as no interest in food , grooming or mating , were chosen and compared to 20 ‘ happy ’ monkeys and 10 that had been kept in isolation and were also thought to be depressed . The researchers found that the naturally depressed and isolated monkeys behaved in a similar way , such as ‘ stereotypical prostrated and socially unresponsive posture as well as exacerbation of socially submissive behaviours , ’ the study said . Naturally depressed monkeys displayed a slumped posture , less interest in feeding and sex and diminished communication and reciprocal grooming with others . 'One to two subjects per stable social colony ( 17–22 subjects ) manifested a depressive phenotype that may be attributed to psychosocial stress , ’ the study said . The authors believe that their monkey model of depression mimics real life and is closer to how depression develops than humans ( illustrated with a stock image ) than rodent models . As well as behavioural changes , they also identified metabolic differences between depressed and healthy monkeys , which has also been witnessed in humans . The healthy monkeys spent longer feeding and drinking compared to their depressed peers who were not as interested in eating , for example . The authors believe that their monkey model of depression mimics real life and is closer to how depression develops in humans than rodent models . ‘ This model 's stable depression phenotype demonstrates superior validity to traditional rodent models of depression by better approximating the psychosocial stressors encountered by adult humans living in a resource-based competitive society and can aid further investigation into the mechanisms underlying depression , ’ they wrote .
Experts from universities in uk and overseas Carolina studied monkeys . shows signs of depression , such as losing appetite and falling over . Unhappiness may be caused by bullying behaviour by dominant monkeys . dominant monkeys in social situation may shed light on human depression .