How? When the population of ancient China started growing (1766-1122 BCE), cooking fuel had to be conserved so that there would be enough for everyone. This caused citizens to chop their food pieces down smaller and smaller so that they would cook faster!
With this new method of bite-sized food pieces, knives were no longer needed and chopsticks were invented to pick up these new food morsels! Some cultures, however, still used a spoon for soup and rice.