Do all animals have brains?
(Lansing State Journal, September 8,1993)


A brian 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.  The level of complexity of a central ganglion roughly parallels the anatomical complexity of the organism as a whole.

Multicellular organisms need to coordinate the activities of their individual cells.  Most animals use a system of specialized cells, called neurons, to help coordinate the activities of different tissues. The exceptions include sea sponges, which are a rather like a loose collection of cells.  Other primitive animals such as jelly fish, do have neurons organized into networks.

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.  As a general rule, animals with more tissue types have more intricate brains.

Both invertebrate and vertebrate animals can have complex brains.  Of the invertebrates, squid an octopuses have the most developed brains, in part to process information coming from their highly sophisticated eyes.  A medium sized octopus will have a brain containing over 100 million neurons, and can show learning behavior.  Still, this is a far cry form mammalian brains that contain on  the order of 10 billion neurons.

Our human brains are remarkably facile in learning, dependable in recollecting and can be quite creative in thinking and expressing a variety of thoughts and emotions.

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