Beer smells like beer and a violet smells like a violet to everyone, right? Maybe not, according to the latest study that traced the way we smell to differences in our genes.
It turns out that our senses are intimately connected to our DNA, and small variations in our genes can determine whether we are partial to the smell of blue cheese, or can’t stand the taste of cilantro. That’s not such a surprise, but what is impressive is the precision with which scientists can match up sensory experiences (such as an appreciation for the spicy scent of curry) to specific stretches of DNA. We may occupy the same environment, but the way we see, smell, taste, touch and hear things may vary widely depending on our genomes.
Perhaps the best example of this gene-based sensory diversity is color blindness — people with genetic abnormalities in the types of cone cells produced in the eye have trouble seeing red, blue or green light. And research has shown that 21% of people from East Asia, 17% of Europeans, and 14% of people of African descent taste a soapiness in cilantro that makes the popular herb unwelcome in their meals. The reason? 23andMe, the company that sequences consumers‘ genes, surveyed 30,000 of their customers and traced the soapy sensation to a gene called OR6A2, which can make some people sensitive to the aldehyde chemicals that flavor cilantro.
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“Because our genes encode the machinery that we use to perceive the outside world, our perceptions of the outside world are all a little bit different,” says Dennis Drayna, a geneticist at the National Institute on Deafness and Other Communication Disorders (NIDCD). “Think about it. You and I know what green is, or what a rose smells like, but does green look to you the same as it looks to me? Maybe, but maybe not. What you and I call green may be slightly different things. There’s no doubt this is going on, and it is going to become better understood.”
How specific is the map tying sensory experiences to genes? Here’s a brief rundown of what geneticists are learning:
In a study published in the journal Current Biology, researchers traced variations in smell sensitivity to four odors to different versions of smell genes. The scientists, from Plant and Food Research in New Zealand, tested 10 different scents in hundreds of subjects, who were provided with wine glasses containing either water or a range of diluted scents.
The four odors related to apples, violets, blue cheese and malt, and depending on the participants’ genetic makeup, their smell receptors either detected the floral scent of violets, for example, or a rancid, acidic smell that wasn’t so pleasant. Or they could either pick out the sour smell of malt — the germinated grains that form the base of beer — or be unable to smell it at all.
“These smells are found in foods and drinks that people encounter every day, such as tomatoes and apples. This might mean that when people sit down to eat a meal, they each experience it in their own personalized way,” said study author Jeremy McRae in a statement.
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In his research, Drayna found that about a quarter of the world’s population does not taste the same bitter sensations as the majority do. His team identified a gene that encodes the TAS2R bitter taste receptor, which is expressed in taste cells on the tongue. There are three different places where the DNA code for the gene differ, resulting in an individual being unable to taste some bitter flavors. He’s also identified specific genetic variants, called SNPs, that explain about 16% of the differences in how people perceive sweets and why some people are less able to taste sweet substances.
“Every single person has had the experience where you look at something and you want to call it one color, and you’re with someone and they want to call it a different color,” says Jay Neitz, a professor of ophthalmology and a color vision researcher at the University of Washington in Seattle. Neitz’s lab has done groundbreaking research into color blindness, even curing the disorder in primates.
Even among those without color-blindness, Neitz says there is a wide variety in how eyes distinguish color. “If you take the rainbow and spread out all the different colors, it turns out some colors almost everyone agrees on how they look, and there are other colors with huge disagreement,” he says.
For instance, almost everyone agrees on what yellow looks like. But if you ask someone to point to what they classify as uniquely green on a color spectrum, there’s huge variability. The same goes for red. “This is one of the things that hasn’t gotten a lot of attention because people have not been able to nail [down] why this is true,” says Neitz. “It turns out that there is variability in the ratio of red and green cones in the eye that’s huge.”
These cones affect how sensitive a person’s eyes are to those colors. Normal-sighted people can contain anywhere from 30% to 95% of red cones, with the remainder being green. Neitz says a series of genetic mutations can affect whether cells destined to become cone cells in the eyes become red or green.
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Scientists are looking into such gene-based differences in the way other senses are perceived too. Some researchers have identified touch genes that help distinguish hot and cold, for example, from studies of people with genetic disorders that prevent them from telling the difference, and Drayna has also looked at the significant variability in hearing among people — from those who are deaf to people with perfect pitch.
The work isn’t just academic. How people sense taste and smell, for example, has a direct connection to what they eat, so testing people for these senses is becoming an important part of nutrition surveys. For example, since January 2013, the National Health and Nutrition Examination Survey (NHANES), an annual government look at eating habits and nutrition among a representative sample of Americans, began asking participants to scratch and sniff cards containing scents of four common food items and four non-food items, and to report what they smelled. To better understand taste differences, the survey takers also apply solutions of various flavors to the tips of participants’ tongues.
“Taste and smell, our chemosensory perceptions, form the basis for what we choose to eat or drink,” said Howard Hoffman, the program director of epidemiology and statistics at the NIDCD in a statement. “Does the ability to taste and smell impact nutrition? I would say so, but in what ways and to what degree remains uncertain.”
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Such data would undoubtedly be helpful to the food industry as well. Manipulating ingredients to counteract the off-putting flavors that some people taste or smell, for example, could expand the market for certain products.
And it’s not just what we eat that is affected by flavor. The Food and Drug Administration recently concluded that menthol cigarettes likely pose a greater public health risk than regular cigarettes, and Drayna’s research suggests that may be due to people’s preference for that flavor, which could induce them to smoke more heavily. “African Americans almost exclusively smoke menthol cigarettes. The menthol receptor is a temperature receptor and menthol is a chemical that activates that receptor, so it produces the perception of cold,” Drayna explains. “Africans have quite a different version of this gene than non-Africans, so we are working to see whether that genetic difference is actually responsible for a perception difference.”
Even beyond the food industry, custom scents are already being exploited by retailers to attract consumers. As Business of Fashion reports, Bloomingdales hired global scent marketing company ScentAir to create different scents for its various departments, such as a coconut fragrance for the swimwear racks and a lilac scent in the lingerie area. Since scent is evocative of emotions and memories, store executives hope that being reminded of pleasant experiences at the beach will entice customers to purchase swimwear.
That connection between the senses and our experiences — to moods, emotions, and memories — is part of our sensory world, and ultimately work in combination with our genes to determine how we perceive everything from foods to scents. “There’s a strong environmental component to food preferences that doesn’t have to do with genetics, but experience,” says Drayna. “But genetic differences are real, and probably very common and we have a lot more to learn from them.”