New York Times: How Caffeine Evolved to Help Plants Survive
“Plants make nectar to feed insects and other animals so they’ll spread their pollen. When insects feed on caffeine-spiked nectar, they get a beneficial buzz: they become much more likely to remember the scent of the flower.” http://www.nytimes.com/2014/09/04/science/how-caffeine-evolved-to-help-plants-survive-and-help-people-wake-up.html?_r=0