What is Cephalization? - Definition & Advantage

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  • 0:01 What Is Cephalization?
  • 1:09 Advantages of Cephalization
  • 1:29 Development of a Brain
  • 2:18 Concentration of Sense Organs
  • 3:07 Mouth Located Near…
  • 3:42 Lesson Summary
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Lesson Transcript
Instructor: Joanne Abramson

Joanne has taught middle school and high school science for more than ten years and has a master's degree in education.

You probably realize that most animals have heads. But some, including starfish, don't. Why is having a head so important to some animals and not to others? This lesson discusses cephalization and why it's so important.

What Is Cephalization?

If I were to ask you to name the parts of a starfish, what would you answer? Well, they obviously have five arms (sometimes more). But what else? Unless you were well versed in echinoderm anatomy, there's a good chance you'd stop there. You may be thinking to yourself right now, wait a minute, starfish are just legs and a body! They don't have a head or anything else. And you'd be right. Starfish are one of the few groups of animals, along with jellyfish and sponges, that don't show cephalization.

In the simplest sense, cephalization means having a head. In fact, the term originates from the Greek word for head, kephale. But there's a little more to it than that. Think about how important your head is and what it contains. Internally, it holds your brain, and externally, it has your primary sense organs (your eyes, nose, ears, and mouth). This is the real essence of cephalization, the concentration of nervous tissue into a single, controlling organ and the organization of sense organs into one area at the anterior (head) end of the body as opposed to the posterior (tail end.)

Advantages of Cephalization

So, why does the majority of animal life show cephalization? Well, this trait holds multiple evolutionary advantages, such as the development of a brain, the concentration of the sense organs at the front of the body, and the close proximity of the mouth to the sense organs. Let's explore each of these advantages in further detail.

Development of a Brain

An obvious advantage of cephalization is the development of a control center or brain. The brain is a concentration of nervous tissue that coordinates and controls sensory information and nervous activity. A larger brain allows for smarter and more complex animals. A more sizable brain is able to control a greater number of specialized organ systems, which leads to more sophisticated animals.

As an example, look at the flatworm, the simplest animal to show cephalization. Its very tiny brain controls eyespots, which allow the flatworm to sense light versus dark. This can't really be considered sight, but it's still an improvement over the jellyfish, which doesn't have this ability. However, compare this to your advanced brain and eyes that not only have true sight, but can differentiate, by some estimates, ten million different colors.

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