Dolphins and whales were already known to have some human-like traits, but a new study has revealed just how similar they really are.

The research, published in Nature Ecology and Evolution, was led by Dr Kieran Fox from Stanford University in California. The researchers looked at 90 species of whales, dolphins, and porpoises, and found a link between brain size and social and cultural traits.

Dr Fox said this research showed that whales and dolphins are able to achieve higher cognitive and social skills than thought. A big unknown, though, is how species that are vastly different – like primates and Cetaceans – are able to develop similar behaviors.

Previous research has shown similarities between marine mammals and humans. For example, bottlenose dolphins can use simple tools, while orcas call each other by name.

However, this is the first study to create a large dataset of the brain sizes of whales, dolphins, and porpoises in relation to their social behavior. And it found “overwhelming evidence” that these Cetaceans have sophisticated social traits, similar to humans.

“[T]he apparent co-evolution of brains, social structure, and behavioural richness of marine mammals provides a unique and striking parallel to the large brains and hyper-sociality of humans and other primates on land,” Dr Susanne Shultz from the University of Manchester, a co-author on the study, said in a statement.

“Unfortunately, they won't ever mimic our great metropolises and technologies because they didn't evolve opposable thumbs."

In the study, the authors outline a number of traits these marine mammals share with humans. For example, they can form complex relationships and work together for mutual benefit. They also teach others how to hunt and use tools, and hunt cooperatively.

Certain groups of marine mammals have regional dialects, just like humans, and they even work with other species to achieve common goals. They will also look after youngsters that aren’t their own, and play together socially.

It’s thought that the large brains of these animals may have grown to support their relatively information-rich social environments. This is the first time, however, that a proper link has been drawn between social behaviour and brain size in these creatures.

“In order to move toward a more general theory of human behaviour, we need to understand what makes humans so different from other animals,” Dr Michael Muthukrishna from the London School of Economics (LSE), another co-author on the study, said in the statement.

“And to do this, we need a control group. Compared to primates, cetaceans are a more ‘alien’ control group."