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Do all animals have brains?

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A brain is defined as the principal ganglion of an animal's nervous system. A ganglion is a collection of nerve cells that process information. It receives in formation from nerve fibers that extend throughout the body of an animal and also may be affected by a variety of hormones. read more

Instead of a brain, jellies have what’s known as a neural net — a system of nerve cells interwoven all over the animal’s body. Jellyfish survive this way whether they’re 1 mm wide or 100 feet long. Sea Sponge. Not only are they brainless, but sponges don’t even have digestive, nervous or circulatory systems. read more

While all of these organisms can sense their environment in some way and respond to it, they do not have brains. Only animals with distinct body cavities possess brains. This includes life forms as diverse as earth worms, clams, fish, insects, birds, and of course, human beings. read more

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