Why have chopsticks been adapted as the primary utensil of choice:
The answer I've been taught my whole life (and I'm Chinese) was that Confucius believed that forks and knives promoted a sort of violence when eating and that it was best to keep weapons off of the dinner table and promote a gentleness when eating. This would follow his philosophical teachings.
Where do chopsticks come from:
The origin of the chopstick itself is fairly unknown, but believed to be an evolution of the ancient chinese who would roast meats over/in coals and use long sticks to fish them out. As food and fuel became more scarce food was cut into smaller pieces to cook more quickly and smaller sticks were needed to pick up the food.
History of chopsticks: http://www.asianartmall.com/chopstickshistory.htm
Confucius and Chopsticks: http://www.chinadaily.com.cn/english/doc/2004-01/09/content_297513.htm