“Your preference for one flavor of ice cream over another is part DNA, part upbringing. wundervisuals/Getty Images
When Shelley Salling, a pharmaceutical sales representative in Kennesaw, Georgia, took a 23andMe genetic test, she expected to learn a lot about her ancestry and her health. But her "trait report" also told her she was likely to prefer chocolate ice cream to vanilla, to be afraid of public speaking and to get up late in the morning.
So, what’s going on here? Could these personality traits really be embedded in your DNA?
Most services like 23andMe, Ancestry and The Geographic Project started off as tools to help people uncover where their ancestors came from. Public enthusiasm over that capability soon led to expanded DNA test options that looked at health predispositions and explored traits that have to do with taste, smell, abilities, physical appearance and more. Some of the answers are fairly easy to reconcile, as most people already know whether or not they have blue eyes, dimples, a widow’s peak or red hair. Others, however, such as ice cream flavor preference, fear of public speaking and hating cilantro might be hard to fathom as DNA-driven.
Turns out it’s not as simple as one isolated public speaking or ice cream flavor gene. 23andMe enlisted thousands of participants to answer a whole bunch of questions and submit their DNA. Then, it looks at the participants’ answers and their DNA to establish connections. If a lot of people who prefer chocolate over vanilla share similar genetic markers, then those markers are identified as possible ice cream flavor predictors. The same goes for fear of public speaking, asparagus odor detection, musical pitch and so on. When a new person’s test comes in, the company checks the DNA against the existing genetic data but that’s not where it ends. "Based on your genetics, and sometimes your age, sex, and/or ethnicity, we create your personal Trait predictions," says the 23andMe site.
So, it’s not just hard-and-fast DNA evidence in play here. "What 23andMe does is they also look at people’s sex and how old they are and create a statistical model and make a prediction," explains Carl Zimmer, author of "She Has Her Mother’s Laugh: The Powers, Perversions and Potential of Heredity." "When they make a prediction it’s better than just a random flip of the coin. It’s around 60 or 70 percent, which is pretty good." However, he notes, "That alone doesn’t tell you it’s all genetic. The marker might not have anything to do with it. It could just be a statistical fluke."
So, some of the results could be accurate and others way off. In Salling’s case, she was told she likely had detached earlobes, was more likely to have bunions and less likely to have a cleft chin In reality, she doesn’t have detached earlobes, has never had a bunion and does have a cleft chin. "I’m also a dedicated early riser, but the test said that I likely wake up at 8:09 a.m., which is definitely off," she says in an email.
Gene Zombies – Or Not
On the accuracy side, her test results correctly predicted that she loves chocolate ice cream and has a fear of public speaking. However, there’s a lot of wiggle room there, as behaviorally related traits are very influenced by circumstances. "Genes play a role, but experience plays a role, too," Zimmer says. "If you grow up being encouraged to speak in public and rewarded for that and so on, even if you don’t have some of those genes that show up strongly in public speakers you might just feel more comfortable doing it."
He adds that people who aren’t exposed to public speaking are likely to be scared of such a situation, no matter what their genetic profile says. "The fact that you can associate some genes with a fear of public speaking is interesting. That doesn’t mean that genes determine whether you’re afraid of public speaking," he says.
Even taste preferences, which are somewhat hardwired, can be altered by life experience. "There are a number of genes that can nudge your preference depending on which kind of genes you inherit," Zimmer says. "There are also other factors we don’t even know about. Maybe you were eating chocolate ice cream one day as a child and you got stung by a bee and have hated it every day since. Genes definitely play a part in whether we prefer ice cream, but to say that a taste preference is inherited is not true."
The takeaway? If you take one of these tests keep it all in good fun, and don’t let it become a self-fulfilling prophecy. "The model does a little bit better than chance. I don’t think anyone should take away from this that we’re zombie products of our genes," Zimmer says. "Don’t think they’re just looking at your DNA and seeing into your soul."
Now That’s Cool
Eye color, one of the most well-known examples of genetics in action, has done a huge about-face in recent years. In fact, since multiple genes are involved in the determination of eye color, it’s absolutely possible (although not terribly common) for two parents with blue eyes to produce a child with brown eyes.