Many people assume the physical basis of language lies in the lips, the tongue, or the ear. But deaf and mute people can also possess language fully. People who have no capacity to use their vocal cords may still be able to comprehend language and use its written forms. And human sign language, which is based on visible gesture rather than the creation of sound waves, is an infinitely creative system just like spoken forms of language. But the basis of sign language is not in the hand, just as spoken language is not based in the lips or tongue. There are many examples of aphasics who lose both the ability to write as well as to express themselves using sign-language, yet they never lose manual dexterity in other tasks, such as sipping with a straw or tying their shoes.
Language is brain stuff--not tongue, lip, ear, or hand stuff. The language organ is the mind. More specifically, the language faculty seems to be located in certain areas of the left hemispheric cortex in most healthy adults. A special branch of linguistics, called neurolinguistics, studies the physical structure of the brain as it relates to language production and comprehension.
Structure of the human brain. The human brain displays a number of physiological and structural characteristics that must be understood before beginning a discussion of the brain as language organ. First, the cerebrum, consisting of a cortex (the outer layer) and a subcortex, is also divided into two hemispheres joined by a membrane called the corpus callosum. There are a few points which must be made about the functioning of these two cerebral hemispheres.
1) In all humans, the right hemisphere controls the left side of the body; the left hemisphere controls the right side of the body. This arrangement--called contralateral neural control is not limited to humans but is also present in all vertibrates--fish, frogs, lizards, birds and mammals. On the other hand, in invertibrates such as worms, the right hemisphere controls the right side, the left hemisphere controls the left side. The contralateral arrangement of neural control thus might be due to an ancient evolutionary change which occurred in the earliest vertibrates over half a billion years ago. The earliest vertibrate must have undergone a 180° turn of the brain stem on the spinal chord so that the pathways from brain to body side became crossed. The probability that such a primordial twist did occur is also born out by the fact that invertibrates have their main nerve pathways on their bellies and their circulatory organs on their backs, while all vertibrates have their heart in front and their spinal chord in back--just as one would expect if the 180° twist of the brain stem vis-a-vis the body did take place.
2.) Another crucial feature of brain physiology is that each hemisphere has somewhat unique functions (unlike other paired organs such as the lungs, kidneys, breasts or testicles which have identical functions). In other words, hemisphere function is asymmetrical. This is most strikingly the case in humans, where the right hemisphere--in addition to controlling the left side of the body--also controls spatial acuity, while the left hemisphere--in addition to controlling the right side of the body-- controls abstract reasoning and physical tasks which require a step-by-step progression. It is important to note that in adults, the left hemisphere also controls language; even in most left-handed patients, lateralization of language skills in the left hemisphere is completed by the age of puberty.
Now, why should specialized human skills such as language and abstract reasoning have developed in the left hemisphere instead of the right? Why didn't these skills develop equally in both hemispheres. The answer seems to combine the principle of functional economy with increased specialization. In nature, specialization for particular tasks often leads to physical asymmetry of the body--witness the lobster's claws--where limbs or other of the body differentiate to perform a larger variety of tasks with greater sophistication (the same might be said to have happened in human society with the rise of different trades and the division of labor).
Because of this specialization, one hemisphere--in most individuals for some reason it is the right hemisphere--came to control matters relating to 3D spatial acuity--the awareness of position in space in all directions simultaneously. Thus, in modern humans, artistic ability tends to be centered in various areas of the right hemisphere.
The left hemisphere, on the other hand, came to control patterns that progress step-by-step in a single dimension, such as our sense of time progression, or the logical steps required in performing feats of manual dexterity such as the process of fashioning a stone axe. This connects with right-handedness. Most humans are born with a lopsided preference for performing skills of manual