Sweetness is perhaps the most primary human taste experience. From human milk, itself being a complex and sweet first drink, to studies done which show that infants can tolerate glucose better than water, we are reminded that sweetness is a core element in life from the very beginning.
Sweetness was of course familiar to our deepest ancestors through ripe fruits, berries, and harvested wild honey. Sugar (refined sugar) is, contrastingly a totally crazy technological invention. Refined sugar is a vegetable product that's been put through the sieve of human ingenuity. Both sugar cane or the sugar beet are today's primary granular sugar sources.
Sugar cane is native to New Guinea and is estimated to have been domesticated around 8000 BC. One Ancient General of Alexander the Great called this "honey without the help of bees."
And just like icing on the cake... the first cake was not iced until the 1600s. Before that, cakes were glazed and the only think remotely like frosting was an early type of marzipan. The first frosty icings were made of sugar, rose water, and butter, and were most often baked into the cake. These were said to be "like ice", hence the contemporary name of icing or frosting.