The word fork is derived from the Latin 'furca' meaning pitchfork, which is what the early designs resembled. The Fork started out life with two prongs, with origins and dates differing, but for arguments sake 400 BCE seems to be a good starting date. By the Seventh century small forks were used at Middle Eastern Courts and made their way to Italy in about the eleventh century in the dowry of a Byzantine princess who married a Venetian doge.
Thanks to Catherine de Medici (who married Henry I in 1533) the fork made its way across the sea to England. It took a while for it to catch on in Europe. By the late sixteenth century, a period when upper-class Italians expressed renewed interest in cleanliness the fork came into use; yet the French court did not pick it up until the seventeenth century when it was deemed uncivilized to eat meat with both hands.
As the saying goes 'necessity is the mother of invention'... so somewhere between the late seventeenth and the mid-eighteenth century, the tines increased from two, to three, to four, in order to make it a bit easier to consume peas, grains, etc. Plus a little curve to the tines allowed the user to scoop up food, besides spear it.
Now we have forks designed specifically to aid us in serving and consuming almost any food you can think of!