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In biology, and more specifically in zoology, cephalization is an evolutionary process that tends to concentrate most of the nervous system, mouth, and sensory organs of an animal with bilateral symmetry at one end of the body .
In simpler words, it refers to the evolutionary appearance of a head where most of the nervous system is concentrated and centralized in the form of a brain, and which also contains the mouth, eyes, nose and other important sensory organs for survival.
Most organisms with bilateral symmetry have an anterior end and a posterior end. The first is distinguished precisely by the presence of the head and because it points towards the preferred direction of movement or locomotion.
Cephalization provides a series of evolutionary advantages that are particularly important for animals that enjoy good mobility, but that are not so important for some species that do not move, or for those that can move indistinctly in any direction.
These advantages have made cephalization one of the most marked and widespread evolutionary trends throughout a great diversity of animal species.
Advantages of cephalization
development of a brain
One of the most important advantages of cephalization is that it leads to the concentration of the nervous system in a single organ, that is, the brain. By having the entire nervous system concentrated in one place, the nerve impulses have to travel less distance, which makes the processing of stimuli from the sensory organs and the production of responses much faster and more efficient.
Much more complex neural networks are also created, giving rise to the intelligence characteristic of vertebrates and other animals.
Greater efficiency in obtaining food
Having the brain, sensory organs and mouth concentrated in the same place helps animals to analyze their environment for food more efficiently and effectively, which represents a clear evolutionary advantage. For example, cats’ whiskers or vibrissae help them detect prey in the dark when they are very close and cannot see it.
Improves targeting and directional scrolling
One of the characteristics of animals with bilateral symmetry is that they move “forward”, in the direction of the plane of symmetry. The presence of a head with most of the sensory organs in the anterior region gives animals a clearer vision of where they are going.
Cephalization during pregnancy
Cephalization is a process so ingrained in our genome that the process of formation of the central nervous system during pregnancy begins very early, just two weeks after conception. It is one of the earliest developmental trends and one of the easiest to detect in the developing embryo.
Examples of cephalization
There are countless examples of animal species that developed heads over thousands and thousands of years of evolution, and they belong to very varied lineages, as presented below:
cephalization of arthropods
In arthropods are invertebrates that include insects, arachnids, myriapods, and crustaceans. Cephalization in these animals occurred through the progressive incorporation of trunk segments towards the head region, which implied the development of more effective mouths when obtaining food. Among arthropods, insects have a high degree of cephalization and a well-marked head, with a brain composed of the fusion of three ganglia.
Cephalization of cephalopods
Cephalopod molluscs are another example of invertebrates with a high degree of cephalization. They include octopuses and squids and have the most complex and highly evolved nervous system of all invertebrates, with a brain-to-body mass ratio comparable to that of endothermic vertebrates. Therefore, these marine animals include some of the most intelligent in the ocean.
cephalization of vertebrates
Vertebrates are the group of animals that include those with the highest degree of cephalization and the most complex and specialized nervous and sensory systems. In addition to humans and other mammals, it includes birds, reptiles, amphibians, and fish. Cephalization in these animals is characterized by the development of large lobar brains, with an immense number of nerve interconnections that make them capable of processing a large amount of information very quickly.
However, it should be noted that not all vertebrates have the same degree of cephalization. In fact, there is a species of fish called amphioxus or lancet fish ( Branchiostoma lanceolatum ), naturally a vertebrate, but with very little cephalization and a “head” almost indistinguishable from the tail. However, this is more the exception than the rule.
