6 Language in the light of evolution and genetics
There is a temptation to assume that that animals are ¡§communicating¡¨; but how, what, and to whom these animals ¡§speak¡¨ are questions to which there are but vague answers.
Animal communication does not merely fascinate us as a zoological phenomenon; it also encourages us to believe that appropriate comparative studies will reveal the origin of human communication. Darwin has shown that man is not the product of special creation but that he descended from more primitive animal forms, neither his structure nor his behavior are special creations.
(1) Straight Line Evolution of language with only Quantitative Changes
This type of theory rests on the belief that there is on essential difference between man¡¦s language and the communication of lower forms. The rather wide-spread belief that many animals have a language of a very primitive and limited kind is easily refutes by a comparison with man¡¦s beginning in language.
Insofar as intelligence is a measurable property within our own species. Man¡¦s language is closely tied to his cognitive structure.
(2) Straight-Line Evolution of complexity by Stepwise Accretion proponents of theories of this type admit of qualitative differences between human and animal communication, but they also believe that the extant communication behavior of animals has a discernible and continuous history. What is important here is that Koehler¡¦s views necessarily imply that language is not a unique and integral behavioral development but a conglomeration of skills and abilities each of which has its own, independent phylogenetic history.
(1) genes and Ontogenetic Development
A very large repertoire of different ¡§instruction¡¨ for different type of synthesis, and these come into play at various stages of development. The puzzle now is : if the inherited genetic information concerns essentially nothing but intracellular events, how could something like the capacity for language have a genetic foundation? Genes can only affect ontogenetisis through varying the cell¡¦s repertoire of differentiation, but this, in turn, may have secondary effects upon structure, function, and capacities.
(2) relative growth
it is interesting to note that the allometric formula also describes a number of quantitative relationship between species.
(3) transformations of form and function
the transformational picture leads us to expect that molecular alterations indirectly caused changes in the temporal and spatial dimensions of the species¡¦ developmental history and that the resulting alterations in structure and function brought with them prolonged and changed periods during which one function could be influenced by others, thus creating critical period of special sensitivities and opening up new potentials and capacities.
There might have been subtle differences in human relations so that even two individuals who are raised in the same home might have experienced different treatment, and identical behavior in apparently different environment. Genetic transmission plays a role in our ability to speak.
(1) Family Histories
After a survey of all published cases we may well agree with Brewer¡¦s conclusion that congenial language disability is probably a dominant, sex-influenced trait with at least fair penetrance.
(2) Twin Studies
All studies agree that fraternal twins are much more prone to differences in language development than identical twins. Fraternal twins who tend to look different will not react to one another as easily as identical ones.
(3) Miscellaneous Evidence
There are some further tantalizing indications for a direct and profound dependence of language capacity on genetic constitution. We still need to wait for further discoveries of speech defects associated with the same chromosomal defect.
There is an inherited error of metabolism producing a disease called histidinemia which particularly affects the development of speech.
(4)The Darlington-Brosnahan Hypothesis
Darlington (1947) proposed that the sound complement of natural language is an expression of its speaker¡¦ vocal preference which, in turns, is controlled by genes.
IV. Limitations on the reconstruction and ¡§Dating¡¨ of the history of language
Reconstruction of the origin of language is impossible except for some very simple determinations. This is because of the following limitations:
(1) the size and shape of the brain furnish no secure clue about the capacity for language;
(2) giving morphological pecularities of the central nervous system do not bear a fixed relationship to behavior; the same cerebral feature may promote somewhat different aspects of behavior in different species, and vice versa; the relation of behavior to certain aspects of the brain may have undergone several changes during the course of evolution of modern man;
(3) even if we had direct knowledge of social structure or cultural complexity of the societies of various fossil men, we could not draw conclusion about language as we know it today. Different types of communication might have prevailed at those times.
The identical capacity for language among all races suggests that this phenomenon must have existed before racial diversification. There is nothing unbiological about recognizing language as unique behavior in the animal kingdom; such uniqueness is to be expected from the evolutionary process as well as from genetic mechanisms.