We talk about knives and forks rather than forks and knives perhaps because sharp-edged things for slicing have been around a lot longer than left-handed prodding and impaling implements.
Knives were always an essential bit of kit - everybody carried one and they were used to kill prey as well as to consume it. But their use as weapons prompted the 17th-century French king, Louis XIV, to order all sharp-tipped knives to be blunted, presaging their present-day shape. Spoons evolved in paleolithic times when people used shells or carved pieces of wood to carry liquid. As with knives, people had their own personal utensil, which explains the custom of giving spoons as christening presents.
Compared with these old tools, the fork is a relatively recent invention. Originally, two knives were used at the table - one to hold the meat and one to cut it - before the twin-pronged fork evolved to do the job. European royal families used forks in the Middle Ages for eating foods that were sticky or might otherwise stain their fingers. But when, in the early 1600s, Englishman Thomas Coryate brought a fork back from Italy - after walking all th way there and back - his imported eating habits were ridiculed as pretentious and cissy.
The familiar three- or four-tined fork, curved to allow the eater a proper view of their meal and carry pieces of food, took its place in the table settings of polite society in the middle of the 18th century.
Picking up food with your hands can get you asked to leave top restaurants quicker than you can say "pass the port", but until cutlery came along it was the only way to eat. In the Indian subcontinent, scooping up food with a chapati or nan bread is the acceptable way of conveying it from plate to mouth, and Chinese chopsticks are Zen-like in their simplicity compared with the hardware we use for hacking and stabbing our food.
Although the etiquette of eating is drummed into us from an early age (don't put your knife in your mouth!), table manners and the proper use of knife, fork and spoon are just social conventions. Modern adaptations such as the spork (the chip shop spoon-fork hybrid) and woon (flat, wooden spoon used to eat cinema ice cream) have their uses but they will never supplant the holy trinity of tableware.