Can you imagine living without a brain? What would be impossible to conceive for a human being is the reality for various species, mainly marine, that feed, excrete, reproduce and can learn from what happens in their environment without the need for that organ.
Jellyfish, starfish, anemones, corals and sea urchins are on the list, but so are they earthworms. Some look like plants or have gelatinous shapes, and many share the characteristics of having a nervous system or, at least, nerve endings. Although there are species that don’t even have that.
The evolution of the brain
Evolution allowed us to advance from the first chemical and electrical messages in multicellular organisms – more than 1.9 billion years ago – to sophisticated nervous systems, where neuronal communication becomes increasingly faster, more precise and complex.
The first nervous systems were nervous networks, which had no central command or brain, which can still be seen in organisms such as hydras and jellyfish. But about 500 million years ago, the first vertebrates developed basic versions of the pattern