The Nervous System in Fish

Even though they do not yet live on land, fish are arguably the first relatable, recognizable animals here. They are reasonably familiar and share a surprising amount of the same traits as us humans, and they have some interesting evolutionary features.

An image of the skeletal structure of a bony fish. From the Bulb Website

These are the first animals to have both a true spinal cord and skull to protect the nervous system. They have a brain divided into five regions: the telencephalon (cerebrum), the dienchephalon, the mesencephalon, the metencephalon, and the myelencephalon.

A diagram of a fish's brain. From The Aquarium Life

They also evolved some additional sensory organs, such as internal ear organs, complex eyes, nostrils, and chemical sensory organs. Some fish can even sense electrical signals in the water!

These advancements allowed fish to become significantly more mobile and to be able to make accurate assumptions about their environment based on the data their brain and sensory organs collect—in essence, these were the first vertebrates with true learning capabilities.