Sponges are among the most primitive of all animals. They are immobile, and live by filtering detritus from the water. They have no brains or, for that matter, any neurons, organs or even tissues. If you were looking for the evolutionary origins of animal intelligence, you couldn’t really pick a less likely subject to study.
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.