Big brained animals have 'platonic friendships'
28 May 2014 Last updated at 16:14 BST
Animals with big brains such as elephants, horses, killer whales and some primates have close platonic friendships, according to the New Scientist.
The friendships, which are not sexual, are formed by animals in stable, community groups.
Wildlife filmmaker Adrian Cale said the friendships helped animals who were finding group living stressful.
He told BBC Radio 5 live's Breakfast: "If you're a lower ranking individual, you're going to find it tough. So therefore you form alliances... defensive coalitions with other animals."