Scientists have long been interested in how animals respond behaviorally, physiologically, and psychologically to the death of a fellow human being, and the mechanisms behind these responses. Complex emotions are not exclusive to humans; chimpanzees, baboons, Sichuan golden monkeys, and elephants, animals with more complex social organization, are now known to show grief after the death of a loved one. But scientists don't yet know if other animals can feel sadness in similar scenarios.

Giovanni Bearzi, a cetacean biologist at the Italian Centre for Dolphin Biology and Conservation, and colleagues at other institutions, analyzed 78 records - responses made by cetaceans after the death of a companion - between 1970 and 2016, covering 20 of 88 extant cetacean species. From these, they found and toothed whale suborder responded more often to the death of a fellow cetacean than a baleen whale suborder. Of these, dolphins in the suborder Toothed Whales had the highest incidence of attentional behaviour to dead companions, accounting for 92.3 per cent of all records, and their attendance index was 18 times higher than the average for all other cetaceans following the death of a companion.

 Scientists analyze that the "social brain" may be behind this behavior. Acquired social activities can have a positive impact on the complexity of the brain. For example, chimpanzee brain dissections show that their brains are under strong genetic control, whereas modern human brains are generally influenced by environmental factors and have little to do with genetics. Of all cetaceans that responded to a dead companion, in 75% of cases (sample size 28) it was an adult female that responded to a dead calf or juvenile individual, and it was most likely their offspring that died. Only 25% of the females would respond to dead adult and subadult companions. This is because cetaceans are mostly matrilineal societies (dolphins), where adult females and juvenile individuals live together for long periods of time and are more socially intimate with each other.