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Why Do Plants Produce Caffeine?

Caffeine is consumed all over the world, in various forms, by many different and diverse cultures. But the question arises, what purpose in the natural world does the chemical serve?

The answer is that caffeine is part of the plant's 'chemical weaponry' to defend itself against predators and competitors. Plants cannot defend themselves with limbs, or run away from danger. Instead, they synthesise chemicals which are toxic to certain life forms. Caffeine is such a chemical; it has potent antibiotic and anti fungal powers, and causes sterility in several insects. Also, caffeine permeates the soil which surrounds the plants by the accumulation of fallen leaves and berries, thus inhibiting the growth of competing plants.

However, in doing this, the caffeine plant ultimately kills itself as well. Over many years, the accumulation of caffeine in the soil becomes so great that the toxicity level is high enough to harm the parent plant. It is this that contributes to the degeneration of coffee plantations between the age of ten and twenty-five years.

Spider web spun under the influence of caffeine

The web is a result of a NASA research project into the effects of certain chemicals on the common house spider. Of all the chemicals tested, including marijuana and chloral hydrate, the web produced by the spider on caffeine was the worst, showing no sign of the 'hub and spokes' pattern that is fundamental to convention web design. When NASA released these results, a New Yorker columnist claimed (probably tounge-in-check?) that the researchers had "identified the drug for human error"¹, but the web only really shows the power of caffeine as an insecticide; the results have no bearing on human behaviour.

¹  New Yorker, June 5, 1995, p.34

Where do we find caffeine? The major natural sources of caffeine...

Competition? Caffeine is not the only stimulant alkaloid which is produced by plants and consumed for the 'kick'...
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Caffeine - Simon Tilling