They also found that humans and octopuses share parts of an ancient messaging system involved in social behaviors, one enhanced by the presence of MDMA in both animals. These shared lineages may have been conserved to reduce fear and enable social behaviors. And although preliminary, the authors think octopuses present a promising model for studying MDMA’s effects on the human brain, treating PTSD and better understanding how the brain evolved to conjure social behaviors.

[Like the Science Times page on Facebook. | Sign up for the Science Times newsletter.]

MDMA helps release, among other chemicals, serotonin. That ancient molecule is involved in regulating mood and social behaviors in invertebrates like locusts as well as vertebrates, like fish, dogs and humans.

For Dr. Dölen, who is interested in evolution of social behavior, the octopus offered an interesting test of MDMA and serotonin, because it is separated by 500 million years of evolution from humans, but also has complex behavior.

Octopuses suspend their aggression for a few minutes to mate, perhaps accessing an otherwise switched-off neural signaling system — potentially similar to the one that helps humans behave socially, she reasoned. And any similarities in octopus and human genetic code related to this system could help her understand how the brain — down to its tiniest bits — evolved to govern social behaviors.

Like a wedge in Pac-Man’s mouth, MDMA fits inside a protein that moves serotonin in and out of neurons. The drug eventually causes a flood of serotonin between synapses, increasing its signals. When the researchers compared the genome of the California two-spot octopus (Octopus bimaculoides) to those of other animals, they discovered humans and octopuses could both make this protein, and it was nearly 100 percent similar at that special Pac-Man spot.