Human evolution has helped shape how we perceive different types of flavors. Scientists believe bitterness evolved to become a defense mechanism of sorts, warning us when the food or beverage may be poisonous.

Yet, we voluntarily consume a range of bitter substances from caffeinated beverages to alcohol. Some of us even develop a strong preference and in extreme cases, an addiction.

As a part of a new study, published in the journal Scientific Reports, researchers from the United States and Australia decided to find out what determines these individual preferences. 

If you had to take a guess, which of the following groups do you think is likely to drink more coffee — people who are less sensitive to the bitter taste of caffeine or people who are more sensitive to it?

In what comes as a surprising finding, the latter appears to be the right answer.

"You'd expect that people who are particularly sensitive to the bitter taste of caffeine would drink less coffee," said Marilyn Cornelis, assistant professor of preventive medicine at Northwestern University Feinberg School of Medicine. "The opposite results of our study suggest coffee consumers acquire a taste or an ability to detect caffeine due to the learned positive reinforcement (i.e. stimulation) elicited by caffeine."

Consider how some people who are unable to fully appreciate a certain song — which in its defense, would be a perfectly good song — because it reminds them of an unpleasant time in their lives.

There may be a similar process of association we employ here with our taste preferences. In other words, we simply learn to associate a bitter taste with good things, Cornelis explained. These "good things" include effects like increased productivity, mental clarity, and headache relief thanks to the stimulating power of caffeine. 

On the other hand, people were likely to avoid coffee and be tea drinkers if they had a heightened sensitivity for two substances known as propylthiouracil and quinine. Our sensitivity to these substances, as well as caffeine, is caused by a genetic variant.

And speaking of genes, Cornelis told NPR the ability to break down and eliminate caffeine from our system also varies from person to person. In fact, she believes this may be the better predictor of how much coffee we drink.

So does this mean our genetics alone determine whether we become coffee drinkers or tea enthusiasts? While it plays a strong role, further studies are needed to examine how far other factors influence our preferences.

In a rather well-known example, tea is often regarded as a British staple and an iconic component of the culture. It may be worth examining how this culture may condition a widespread preference for the beverage.