Wild elephants could be the next animals to join an exclusive list of species that show signs of self-domestication. A study published April 3 in the journal Proceedings of the National Academy of Sciences (PNAS) found that elephant self-domestication may have led to some of their advanced traits, such as mourning their dead, helping sick or injured elephants, and even recognizing themselves in mirrors

According to  the self-domestication hypothesis, humans have gone through a process of “selection against aggression,” that was self-induced and not forced.  

“The theory of self-domestication is hard to test,” study co-author and Max Planck Institute evolutionary biologist Limor Raviv said in a statement. “This is because only one other species besides humans has been argued to be self-domesticated: bonobos.”

[Related: A DNA tool designed to solve murders is exposing elephant poachers.]

Raviv and her colleagues looked at how African savannah elephants compared with humans and bonobos on 20 different measures. They found that all three species share some of the same physical features and display the same habits. Elephants play, are social, have a long childhood, and “babysit” for the offspring of other members of their groups. Both bonobos and humans also do this. Additionally, wild African elephants’ have a shortened jawbone, which is a trait shared by domesticated animals such as cats.  They also appear to be able to restrain themselves from being aggressive to others.

Elephants can also learn from each other. Knowledge like what to eat and how to raise their young are socially transmitted, versus being innate like they are in other animals. For example, spiders are born knowing how to spin silk, same goes with birds building nests. Elephants also have a sophisticated and varied communication system. Their extensive vocal repertoire ranges from roars to low-frequency rumbles to trumpets and roars to low-frequency rumbles. Elephants in Kenya even have a different alarm call for bees than they do for humans. 

The team also found several candidate genes associated with domestication in elephants. They compared the genomes of wild elephants with studies of 261 domesticated mammals and created a list of the genes that are frequently associated with domestication. Of the 674 genes that the team says have a high likelihood of being passed down from earlier elephant generations, 79 genes were associated with domestication in other species. This could suggest that domestication can evolve in multiple branches of the mammal evolutionary tree. 

[Related: ‘Zombie genes’ could be why so few elephants die of cancer.]

The team hypothesizes that self-domestication in elephants might be related to their large size and relative strength. “This means that elephants are generally less worried about evading or fighting other animals for their survival,” Raviv said. “This kind of ‘safe environment’ could relax selective pressures for aggression, free cognitive resources, and open up more opportunities for exploration, communication, and play.”

Some scientists remain wary about self-domestication in general and future studies are needed to further test this hypothesis. Melinda Zeder, an emeritus archaeologist and domestication expert at the Smithsonian Institution told Science, “it’s nice to see the correlations with bonobos and humans and the genetic similarities tied to the reduction of aggression,” but she is still skeptical of the self-domestication idea in general. She adds that self-domestication is a “meaningless term that muddies the waters,” and that domestication requires “two to tango,” meaning a domesticator and a domesticate.