Certain evolutionary processes seem characteristic of language,
and are not found in other areas of evolution, such as biology or culture,
or at least not so obviously. One of these is lexical diffusion-the spread
of an innovation from one word to other similar ones. For example, in English
the past tense can be indicated in several ways, either by adding the suffix
ed (changing love to loved ) or a different suffix, or even
by changing root. These last two types of verb are termed irregular, and
examples are find (found) and ,go (went). The number of regular
verbs has increased considerably since medieval times; this process of simplification
has accompanied the various transformations of English down the centuries.
Cases of lexical diffusion where a given form or, more precisely, a particular model is progressively adopted by analogy are fairly frequent. In Italian, we find that the letter n before s followed by another consonant (known as the impure s) has been dropped. So inspiration has become ispirazione, transport has become trasporto, and Institute has become Istituto. French, and the Latin original, of course, have kept the n, so that the French translation is traslazione in Italian.
In a talk he gave as president of the American Language Society, the Philadelphia sociolinguist William Labov stated that the recognition of lexical diffusion by William Wang of Berkeley has constituted one of the greatest steps forward in linguistic evolution in recent times. Labov is now examining whether a phenomenon recently appearing in many languages, and with singular emphasis in English, can be considered an example of lexical diffusion. It is one of the most interesting developments in the English language since medieval times. Called "the great vowel shift," this complex phenomenon is a major culprit in the marked divergence between English spelling and pronunciation. When this shift began, there were a limited number of vowel sounds in English (about seven, in line with other Latin-derived languages, where the five written vowels have seven sounds because e and o can both be pronounced either open or closed). Currently, English has about twenty distinct vowel sounds and a large number of diphthongs.
In the Middle Ages, many words such as "bite," "mite" and "white" were pronounced like an Italian or Spaniard would pronounce them today. It is not easy to render this pronunciation with modern English spelling, but it would be something like that of words "beetay," "meetay," "wheetay," except that the final y would not be heard. But starting in the fourteenth century and going through a series of stages, more or less the same for all words, the last vowel was dropped and the first became the diphthong "ai," like in the modern "received pronunciation" (British upper class, and BBC of some years ago). In phonetic spelling, the original i became first ii then ei (as in wait) and finally ai (as in white). In some parts of the UK the various older pronunciations are preserved; in others, the pronunciation has gone one step further or in other directions. For instance, in the London dialect (Cockney) and in Australia (many of the first Australian settlers were from the London jails) the diphthong of "bite, mite, white" had become of. Lexical diffusion assured, of course, that all similar words acquired the same sound. In these last regions, another vowel shift affected words like "mate" (meaning pal), "rate," "wait" and "bait" . It seems as if, in the English upper classes, these words are still at the "ei" stage, while in Cockney and Australian they have reached the next stage, "ai" .
A well-known linguist, E. Sapir, has called this unidirectional parallel variation "drift."...to drift means "to be drawn by a current," and currents have a fixed direction....
With a reasonably ample definition, it seems that lexical diffusion can be extended to include the classic "phonetic laws" established in the nineteenth century. "Phonetic laws" describe the regular way in which sounds change. They have been proved and applied on many occasions particularly in the nineteenth century. Among these are the famous Grimm laws (defined by the excellent linguist Jacob Grimm, who together with his brother also wrote the famous fairy tales). For example, p, t, and k in ancient languages (Greek, Latin, or Sanskrit, that is) become f, th, and h in English, and f, d, and h in High German. So pater is father in English, fadar in Gothic, and Vater, pronounced "fater" with a long a in modern High German). A group of late-nineteenth century linguists, the neogrammarians, were convinced that the rules for changes in sound are perfect, and that all exceptions can be explained. This is an exaggeration, but it must be admitted that sounds change with astonishing regularity. It is reasonable, therefore, to seek an explanation in some biological substrate.
Another well-known linguist, Noam Chomsky, recognized that
language has a profound structure, manifested by humans' ability to perceive
subtle differences between superficially similar-sounding phrases. He suggested
that the human mind has an innate capacity for language, meaning that in
his opinion there is a unique and special biological basis to language.
It is easy to be less enthusiastic than his more ardent disciples about
many details of Chomskis theory, but there is undoubtedly truth in the affirmation
that the human mind has a predisposition for language. Animals, even those
closest to us, don't have this predisposition and probably never achieve
our degree of eff'ciency and complexity of usage. This unique aspect of
the human mind has so far manifested itself in two ways: the enormous interest
displayed by a normal child in learning language in order to be able to
communicate with adults and other children, and the presence of special
abilities with a genetic basis, which allows us to absorb the finer details
of the use of language and its structures.