This thought came to me while I was cleaning my closet. Now the obvious thing is that the entire body is controlled by action of the brain/central nervous system. What people may think is that zombies are brain-dead, as in, their brain is no longer functional, so they are practically walking dead people. That may not be the case, because the only way the body can even work is by command of the brain. This means that the brain of a zombie isn’t dead, it is simply working differently. Now in theory, zombies aren’t as smart as normal people, they act mainly by instinct (without thinking at all), and they also have no sense of coordination or specific speech. This would mean that the part of the brain that controls voluntary action is dysfunctional, and the parts that control thought, speech and other non-instinctive factors are completely denatured. This decreases the capacity of the brain being used from the normal human brain capacity.
Basically, the most functional areas of the zombie brain would be the areas that control the five senses: sight, smell, touch, hearing and most importantly, taste. And because they would run only on instinct, they can be likened to animals. And if we consider them as animals, that would mean they are of a different species to humans completely. Of course, no real assumptions can be made, because zombies can be the new species that would come to replace the human race, being an evolved and superior species.
Well, we’ll find out someday. I’ve got to study the function of nucleic acids right now.