Some Like It Hot!
Capsaicin, the water-lover
In one study, scientists have found that where a chili plant grows determines how hot it will be. The wetter the place is, the hotter the chili can afford to be. Why? Because making the chemical capsaicin, which is what gives a chili its “hotness” is an expensive process for a plant. It takes a lot of energy to make those spicy fruits (chilies). If there is less water in the ground during fruiting season then the plant conserves its energy and makes less (and less hot) chilies. The plants that grow in areas of plenty water do not have that problem.
There is a reason for this. Spicier plants have more stomata (the little pores on leaves that exchange air and water from the plants) than non-spicier ones. That is why spicier plants have a tougher time during droughts (more pores means more water lost) than non-spicy plants. It could be that the same genes that control making of the pores also control the making of capsaicin. This would explain both the observations.
The "spiciness" of a chili is measured on a Scoville Scale. Here is the Wikipedia link, where you can see for yourself, how hot that chili you just ate, is!
Capsaicin, the anti-fungal
Here’s another angle. Where there is water, there are fungi. These fungi need to be fought off for the plants to be healthy. Guess what chemical is useful in fighting off fungi? You got it. Capsaicin! The more the capsaicin, the easier it is for a plant to fight off disease. So the spicier, hotter chili plants can do this better.
Capsaicin, the cancer-killer
Which leads us to the next finding. That capsaicin has also been found to arrest growth of cancer cells! A new research done by Nottingham University, UK, has found that capsaicin attacks the energy producing areas of cancer cells and triggers cell-suicide. It has not been found to harm healthy cells. Can this explain why people who traditionally eat a spicy diet have been found to have lower incidences of cancer than those that do not? It may be too early to tell for sure, but capsaicin seems like an interesting chemical to watch out for, don’t you think?
Short video on why chilies and peppers are hot: