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The Genetics of Nose-Picking

I’ve been bombarded lately with news releases reporting links between behavior and DNA.

In simpler times, genes encoded proteins, and the actions or absence of those proteins caused the trait or disease. But today, investigations from outside genetics – reported in psychology and politics journals, for example – are assigning genetic explanations to everything from liberalism to feelings about the death penalty to whether the sound of someone chewing is annoying.

Strange things can happen when non-geneticists publish genetics papers. So I thought I’d mention a few intriguing reports and propose a behavior to investigate: nose-picking.

The giraffe's tongue facilitates nostril exploration.
The giraffe’s tongue facilitates nostril exploration.

STRATEGIES

Here are the steps of many behavioral genetics studies:

1. Identify an interesting behavior.
2. Choose populations to sample.
3. Select the type of genetic interrogation. These might include:
• A genome-wide association study (GWAS) of single nucleotide polymorphisms (SNPs) (translation: markers across the genome).
• Identifying variants of specific genes that make sense, such as those that encode enzymes needed to make or break down neurotransmitters or their receptors.
• Exome or genome sequencing.
• An old-fashioned twin study, to see if the trait is shared more often among identical twins than among fraternal twins.
4. Deduce genome parts that those with the characteristic share.
5. Find the targeted genome regions in other animals, such as chimps, wombats, and cockroaches, to probe the evolution of the trait.
6. Publish a paper that describes the compelling genetic association to the behavior, hypothesize a biological mechanism, list caveats and limitations, but reach no conclusions.
7. Have your institution or company distribute a news release that claims that you have discovered or proven the genetic underpinnings of the behavior, so that its occurrence can be predicted in all newborns, and possibly even prenatally.
8. Watch the “content” percolate verbatim to the aggregators, then beyond, as even the weakest of associations becomes genetic fact within hours.

PRECEDENTS

Donald_Trump_-_Caricature_(23414300891)Despite the recent flood of behavior-genetics papers, my favorite remains The Genetics of Politics: Discovery, Challenges, and Progress, from 2012. It reviews studies, mostly of the twin variety, seeking genetic connections to such traits as ethnocentrism, morality, opinion of unions and abortion, and left–right orientation. The paper cites the compelling “Friendships Moderate an Association Between a Dopamine Gene Variant and Political Ideology,” for example. It reveals that people who have the 7R variant of the dopamine receptor D4 gene (DRD47R) and have many friends tend to be liberal, but people who have a different variant and also have a lot of friends tend not to be liberal. Who knew?

Other gene-behavior links include:

• A dopamine receptor gene variant (DRD2A1) that made 53 overweight Asian-American college students want to eat more carbs and fast food, from the Asia Pacific Journal of Clinical Nutrition. The news release suggests that doctors should apply the findings to advise any patients of Asian descent on how to eat well.
• “On the Heritability of Consumer Decision Making,” from the Journal of Consumer Research. The 2011 twin study discovered that “people seem to inherit the following tendencies: to choose a compromise option and avoid extremes; select sure gains over gambles; prefer an easy but non-rewarding task over an enjoyable challenging one; look for the best option available; and prefer utilitarian, clearly needed options (like batteries) over more indulgent ones (gourmet chocolate).” They also found an inherited fondness for chocolate, mustard, hybrid cars, science fiction, and jazz. Tendencies not heritable include “likings for ketchup and tattoos.”
“If you make impulsive choices you should blame your parents — it’s genetic!” shouts the news release, which purportedly follows a trait called “delay discounting.” The media loved this one.

"7 years of college, down the drain."
“7 years of college, down the drain.”

• The social mobility and educational attainment study used a “polygenic score” and was widely reported, although the abstract of the actual paper ends with the head-scratcher: “Factors connecting DNA sequence with life outcomes may provide targets for interventions to promote population-wide positive development.” It offers lots of large numbers with small effect. The trait “years of educational attainment” evokes John Belushi’s character in Animal House, bellowing “Shit! 7 years of college down the drain!” Presumably Mr. Blutarsky had damning variants of several of the “74 areas of the human genome associated with educational attainment” that the study helpfully found.

With all of this inspiration, I decided to adapt a real news release, with enough revision to fly under the search engine radar (I hope).

For Immediate Release

RESEARCHERS IDENTIFY GENETIC LINKS TO NOSE-PICKING

A multinational team has discovered 18 regions in the human genome that may house gene variants implicated in nose-picking, a highly conserved adaptive behavior to clear nasal passages.

Dr. Jerry Seinfeld and colleagues from Alfred E. Neuman University and the University of Papua New Guinea conducted a genome-wide association study using 5,243,593 SNPs on nearly 118,000 people, representing the Estonian biobank, the Inuit genome project, retirees in Santa Barbara, six Neanderthal genomes, the Sardinia Study of Aging, a group of Australian aborigines, and residents of Park Slope, Brooklyn. The team validated the significance of the 18 genome regions in an independent population of elite runners of Ethiopian descent, whose slim fingers might be hypothesized to facilitate probing of the nostrils.

Dr. Seinfeld
Dr. Seinfeld

The results are consistent with a study from 1976 that demonstrated an astonishing similarity in nose-picking behavior among 17 pairs of identical twins separated at birth but not among 11 pairs of fraternal twins, establishing a clear genetic link. The existence of nose-picking among several types of mammals that have different mutations in two of the studied genome regions indicates at least two independent origins of the habit.

“Our findings demonstrate that, even for a behavioral phenotype that is mostly environmental, a well-powered GWAS can reveal potentially relevant biological pathways,” said Dr. Seinfeld. However, the study, despite its breadth, is preliminary, he added. “Efforts to identify candidate genes residing in the 18 hot spots are underway. One possibility is the endocannabinoid system that underlies habitual behavior.” A follow-up study will compare the behavior among attendees of a Phish concert in Saratoga, New York (which I can report on) to nose-picking among an orchestra crowd a month later.

A WORD ON GENETIC DETERMINISM

It doesn’t take much to make news these days, and “blaming genes” is always an enticing topic. But with so many people not reading farther than a headline popping up on Facebook, the nuances of genetics, limitations of experimental design, and appropriate caveats are lost — such as confusing inheriting a behavior with imitating one. And that can be dangerous.

Should a young teen in a family of Republicans automatically vote for Donald Trump?

Does a study on a handful of overweight Asian-American college students who eat too many donuts mean that all Asians should eschew donuts?

And don’t get me started on the geneticization of shopping preferences, social mobility, and educational attainment.

It’s easy for me to poke fun at seemingly superficial and harmless studies, but what connects them is serious: genetic determinism, the idea that our genes control everything. They don’t. Assuming that genes explain all robs us of hope, motivation, control of our lives, and opportunity for change.

Discussion
  1. You ought to love this, from the New York Times;

    “Maternal inheritance also gave rise to the idea that there exists a “Mitochondrial Eve,” a woman from whom all living humans inherited their mitochondrial DNA.”

    http://www.nytimes.com/2016/06/24/science/mitochondrial-dna-mothers.html

    Sorry, I couldn’t resist. In a comment that I left on an earlier article of yours, I made the mistake of not expressing myself explicitly enough. Just sayin’, at least I know what the science says.

  2. Thanks! The New York Times oversimplifies and leaves out important info quite often. They also use teleological language for evolution, such as “evolved to” as if there’s some conscious thought behind natural selection. They also make the genetic code error (when they mean DNA sequence) and my favorite, variations on “stem cells give rise to all types of cells,” forgetting the self-renewal that is key to the very definition of stem cell.

  3. You imply that behavior geneticists who find an association between genes and behavior automatically jump to the conclusion of “genetic determinism: the idea that our genes control everything.” Nothing could be further from the truth. Behavior geneticists clearly recognize and explicitly acknowledge that the associated genes rarely explain over a small fraction of the trait variance leaving the environment to play a clear role in explaining differences in the behavior for traits that are polygenic rather than Mendelian.

  4. Actually, the behavioral geneticists and their papers go out of their way to qualify their findings, and many explicitly state that the associations are perhaps not that strong. It is the media, and especially the people who write the headlines and the news releases, who jump to conclusions.

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