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Let us take the instance of humans and chimpanzees. Chimpanzees are able to express a wide range of emotions тАУ such as busting out in laughter or smiling тАУ this trait was once thought to be a feature exclusive to humans. The smile can be linked to the activation of the brainтАЩs limbic system тАУ where the orbicularis oculi muscle involuntarily contracts and raises the cheeks, forming wrinkles around the eyes. This implies that the smile is a true and genuine smile. Interestingly, this type of reflex has a name тАУ the Duchenne smile. Moreover, research has shown that chimpanzees share 98.6% of our DNA тАУ This means that humans and chimpanzees shared a common ancestor eons ago. It is important to also note that chimpanzees are the closest living relatives to humans.