Spices add flavor and aroma to food through their essential oils. They develop over millions of years in specialized plant cells and can occur throughout the plant, though often concentrated in leaves and seeds. Without spices, the world's cuisine would be bland as spices transform ingredients and identify global cuisines, with some like black pepper and cinnamon used for millennia in places like India for both food and medicine. Spices are what allow humans to enjoy delicious meals today.