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Tuesday, January 16, 2007

Why do animals have heads?

In previous posts, I mused about why there is sex, and why living things have cells. See the latter post for some discussion of what "Why?" means. Here, I mean "What is the function?" or "What good does it do them?"

A head is a structure, at one end of an animal, that has a concentration of important organs. It contains the brain, some sense organs, and a mouth. In some organisms, such as ourselves, a head is usually clearly defined from the neck. In other organisms, like fish, it isn't. In the Arthropoda, which include insects and spiders, heads are often even more clearly distinct from the rest of the body than they are in vertebrates, like humans or elephants. Many kinds of animals, but not all, have heads. The Echinodermata (starfish and their relatives), the sponges, and other types of animals do not have heads. But the vertebrates, and the Arthropods, which are the types of animals we are most likely to see, do.

Having a lot of sense organs in one place, especially in a place at the front of your body, the part that goes into any new area first, is useful. Being able to see, hear, and smell what you are about to get into before you get there can help you change your mind about where you are going to go, or about how to act when you get there. Having these senses in the head accomplishes that. But why the head? Wouldn't it be even better to have, for example, eyes, nose and ears on our hands? That way we could look, smell, and hear around corners, or behind and in front of us at the same time. The answer appears to be rapid communication. It takes some time for a message to get from the sense organs to the brain. The further away they are, the slower is the reaction. So having sight, smell, and hearing (and also taste, balance, and some of the touch sensors) in the head means quicker reaction time, which may make the difference between life and death. (It is also true that hardly any other organism has structures like the hands, which are flexible, and can go anywhere -- most vertebrates use their "hands" to walk on.)

Another thing the head can do, at least in vertebrates, is to provide protection for the brain. The skull helps with that. It also protects the sense organs and the mouth, but the brain is especially well protected. If the brain, and the skull, were located anywhere except at an end of the body, there would probably be serious interference with digestion and other functions.

I'm glad I have a head, and I hope I use it for God's glory. Thanks for reading.

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