Asked by: Focus
Questions regarding the mental state of animals inevitably run onto a philosophical sandbank because we cannot be sure how self-aware animals are. We assume that other people think more or less the same way we do because language allows us to describe our thoughts. We don’t have enough of a shared vocabulary with animals to apply this test and humans are notoriously prone to projecting their own emotions and feelings onto animals. Having said that, many mammals have been observed exhibiting the symptoms of clinical depression (including lethargy, compulsive behaviours, disrupted appetite and sexual interest and even self harm). Zoo animals in particular are prone to this.
Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.