One of my favorite long walks here in Exuma takes me through the Ramsey-Mount Thompson gardens, a strip of fairly arable soil between the beach dunes and the rocky rising ground behind. Onions, cabbages and bananas are the staples, but onions grow best. They are on the Exuma coat-of-arms.
Onions are one of those foods we eat for flavor rather than nourishment. The distinctive tastes and aromas are based on sulfur, which the plant takes from the soil and turns into "ammunition" compounds. These wait in the plant's cells until an animal comes along and tries to eat the plant. Damaged cells release "trigger" enzymes that break the sulfur compounds apart into obnoxious, irritating molecules. One of those compounds makes us cry when we slice a raw onion; we are being zapped by a highly evolved defense mechanism.
Cooking transforms these sulfur-based molecules into the savory flavors we love.
Anyone who enjoys cooking or eating should own Harold McGee's On Food and Cooking: The Science and Lore of the Kitchen -- from which I fetched up this onion lore. There you will find the entire chemical and cultural history of this and every food -- etymologies, origins, etc. McGee adds an intellectual fillip to the sensual experience of eating -- another proof that science and spirit are mutually enhancing.