So it was with great surprise that Onur Sakarya from the University of California, Santa Barbara found that sponges carry the beginnings of a nervous system.

With no neurons to speak of, these animals still have the genetic components of synapses, one of the most crucial parts of our nervous system. And their versions share startling similarities with those of humans.

Synapses are junctions between two nerve cells that are allow them to pass signals to one another. These messages are carried by molecules called neurotransmitters that cross the synaptic gap. When they reach the receiving cell, they come across an elaborate tangle of proteins called the post-synaptic density (PSD; labelled in red below). The PSD processes