Our tongues have several kinds of taste receptors, one of which detects bitterness in whatever it comes in contact with. In many species, this is an adaptive warning signal that something is not good to eat. That served our distant ancestors well, but modern humans are different. We actually seek out bitter foods like beer, coffee, chocolate, tea, and certain vegetables, and we even forget that these things are supposed to be bitter. How we got this way is combination of a number of factors, which MinuteFood explains.