On liking it hot
Photo by papalars. Found on Flickr
The story of how chilies got their heat is pretty straightforward. A recent study suggested that capsaicin is an effective defense against a fungus that attacks chili seeds. In fact, experiments have shown that the same species of wild chili plant produces a lot of capsaicin in an environment where the fungus is likely to grow, and very little in drier areas where the fungus is not a danger.
From the New York Times article A Perk of Our Evolution: Pleasure in Pain of Chilies (log-in required)