|MadSci Network: Other|
Thank you for your question, a subject which interests me a lot. I have found, however that the question was asked previously to Mad Sci. Daniel Fletcher has provided two good answers (linked below) and I will summarise the main reasons he gives for linguistic change, and then look at the evolution of English in a little more detail.
Diffusion - When languages come in contact with each other, they influence and change each other forming Pidgin and Creole languages. Diffusion usually becomes it's own language, after a period of time. Modern European languages, such as Dutch and English, came from ancient German languages such as Anglo-Saxon with a bit of Latin, Greek and others.
Isolation - This is the opposite of diffusion, when a language group is isolated geographically from other language groups and does not change (by diffusion) over long periods of time. Sometimes, two groups that spoke the same language no longer do, because one changed (for other reasons) and the other did not. On Pitcairn Island (where the mutineers of The Bounty landed) the people on that island still speak English the way it was spoken when the British sailors arrived on the island more than 125 years ago.
A mixture of these two factors tends to be one of the main causes of new languages forming, as a group separates and each evolves separately. The evolution tends to be caused by the following effects.
Environment - Languages reflect the important aspects of culture: Politics; Religion; Cross-cultural contact and so on. In recent years the computer age has added a vast range of new words, such as 'internet', and new meanings of old words, such as 'mouse'. Also, groups that live in different environments will have languages that reflect that difference - the English have a vast vocabulary to describe rain, a common feature of the English climate.
The Castilian Effect - Fletcher describes this unusual effect, found in Castilian Spain, where they speak Spanish with a lisp. They do this because one of Spain's former kings spoke with a lisp and everyone in the country did so to make him seem correct.
To look at your examples of English and Dutch in a little more detail. Both have evolved from Germanic roots, part of the Indo-European group of languages. Originally, the inhabitants of Britain spoke a Celtic language which was quickly pushed into Wales and Scotland by the Angles, Saxons and Jutes, invaders of Britain during the 5th Century AD from what is the present day Denmark and northern Germany. The Angles were named from Engle, their land of origin and their language was called Englisc which gave us the word, English. Anglo-Saxon later developed into old English, Middle English and finally Modern English.
Apart from Anglo-Saxon words (answer, folk, freedom, life, love, night, year), numerous world languages have diffused words into English, even Dutch: brandy, decoy, landscape and schooner. Others include: African Languages (banana); Arabic (alcohol); Native American (chocolate, tobacco); Oriental languages (ketchup, tycoon); Indian Languages (bungalow, thug); Italian (arcade, concerto); Latin (refrigerator, tradition); Greek (alphabet, rhythm, telegraph) (television is a mixture of Greek and Latin!); French (Modern: garage, police; Norman: beauty, peace, people); Nordic (fog, window).
Dutch, too, has evolved and changed since the first Germanic settlers arrived in that part of Europe, and interacted with other cultures such as the Flemish, French and Romans. The language has separated from modern German, as the 'Low German' language of the Netherlands separated from the 'High German' of modern Germany. The link can still be seen, however, in the German word for German, Deutch.
I hope all this helps,
With many thanks to Mr Fletcher for:
How do certain areas develop their own accents?; and
How did different languages evolve?:
and to Krysstal and about.com for info on the Development of English.
Try the links in the MadSci Library for more information on Other.