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Tongue Rolling and 5 Other Oversimplified Genetic Traits

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Can you roll your tongue? If so, you’re part of the majority. Between 65 and 81 percent of people on Earth have this strange and seemingly arbitrary talent. But why can some do it while others can’t? The most common answer, the one often taught in elementary schools and museums, is that it’s all about genetics. The story goes that, if you inherited a dominant variation of the “tongue rolling gene” from one of your parents, you too will inherit this party trick. In other words, if you can’t do it, blame mom and dad.

But John H. McDonald, a professor in the University of Delaware department of biological sciences, calls B.S. “If that were true, you could never have two non-rolling parents that having a tongue-rolling kid,” he says. “Yet people have looked at families and find you do see that.”

According to McDonald, teachers and textbooks have been over-simplifying this story for decades. The genetic theory of tongue-rolling can be traced back to a 1940 study by a scientist called Alfred Sturtevant that was quickly debunked. “By the early 1950s, people knew pairs of twins where one could roll and one couldn’t,” McDonald says. “That pretty clearly tells you it’s not all genetic. Yet I ask even today my students ‘how many of you have been told that tongue rolling is a simple genetic characteristic?’ and most raise their hands.”

The truth is a bit more complicated. McDonald says that in some cases, the environment plays a part. It's “nature vs. nurture” in action—many people can break genetic bounds and teach themselves the sacred art of tongue rolling. In other cases, it could just come down to a developmental quirk, like your position in the womb, he says.

So why has this rumor persisted? “It would be really nice to have a biology experiment you can do just by looking around the room,” McDonald says. But spreading these kinds of inaccuracies can be really dangerous. “It is an embarrassment to the field of biology education that textbooks and lab manuals continue to perpetuate these myths,” he writes. “If students took it seriously, a large proportion of students would look at mom and dad and conclude that the mom was sleeping around and dad wasn’t really their dad.”

Tongue-rolling isn’t the only genetic trait we’ve oversimplified. Here, a few other examples McDonald says he's debunked.

1. Hand-clasping

The myth: Whether you put your left thumb on top or your right thumb on top when you clasp your hands is determined by a single gene.

The reality: Even identical twins have different preferences for how to clasp their hands, indicating that there isn’t a “left thumb on top” gene.

2. Eye color 

The myth: Blue eyes are determined by a single recessive gene. A brown-eyed kid cannot have two blue-eyed parents.

The reality: “Eye color is determined by variation at several different genes and the interactions between them,” McDonald says. “This makes it possible for two blue-eyed parents to have brown-eyed children.”

3. Hair color 

The myth: Red hair is determined by a single gene that yields to other colors. Two red-headed parents cannot have a non-red-haired kid.

The reality: There are many variations in the gene that controls red hair pigment, and this gene can be influenced strongly by genes that control brown hair. Indeed, two parents with red hair can have kids with brown or blonde hair.

4. Attached earlobes 

The myth: Everyone has one of two kinds of earlobes: attached (connecting directly to the side of the head) or unattached (a slight separation causing the lobe to dangle). A single gene decides the fate of your earlobes.

The reality: Our earlobes don’t fall into two categories. Instead, there’s a sliding scale between attached and free. Two of the early studies on attached versus unattached earlobes disagreed on which was the dominant trait, showing that the genetics involved aren't as simple as many have been taught.

5. Hitchhiker’s thumb 

The myth: Your thumb is either straight or bent at the knuckle. The latter is called hitchhiker’s thumb, and whether or not you have it comes down to a variation in a single gene. “If the myth were true,” McDonald writes, “two parents with hitchhiker's thumb could not have a child with a straight thumb.”

The reality: There can be no clear-cut definition of a hitchhiker’s thumb because thumb flexibility ranges dramatically from person to person. “It’s completely arbitrary where you draw the line between straight and angled,” McDonald says. Parents with bent thumbs can produce kids with straight thumbs.

The moral of the story? Genetics are complicated. If you really want to see basic genetic traits in action, McDonald suggests looking at cats instead of humans. “Cats do have a number of traits—long versus short hair, orange versus black hair, white boots or not that—that are nice, simple, one gene-traits,” he says. “Everyone either has a cat or knows someone else’s cat.”

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Space
Look Up! The Orionid Meteor Shower Peaks This Weekend
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Ethan Miller/Getty Images

October is always a great month for skywatching. If you missed the Draconids, the first meteor shower of the month, don't despair: the Orionids peak this weekend. It should be an especially stunning show this year, as the Moon will offer virtually no interference. If you've ever wanted to get into skywatching, this is your chance.

The Orionids is the second of two meteor showers caused by the debris field left by the comet Halley. (The other is the Eta Aquarids, which appear in May.) The showers are named for the constellation Orion, from which they seem to originate.

All the stars are lining up (so to speak) for this show. First, it's on the weekend, which means you can stay up late without feeling the burn at work the next day. Tonight, October 20, you'll be able to spot many meteors, and the shower peaks just after midnight tomorrow, October 21, leading into Sunday morning. Make a late-night picnic of the occasion, because it takes about an hour for your eyes to adjust to the darkness. Bring a blanket and a bottle of wine, lay out and take in the open skies, and let nature do the rest.

Second, the Moon, which was new only yesterday, is but a sliver in the evening sky, lacking the wattage to wash out the sky or conceal the faintest of meteors. If your skies are clear and light pollution low, this year you should be able to catch about 20 meteors an hour, which isn't a bad way to spend a date night.

If clouds interfere with your Orionids experience, don't fret. There will be two more meteor showers in November and the greatest of them all in December: the Geminids.

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science
11-Year-Old Creates a Better Way to Test for Lead in Water
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In the wake of the water crisis in Flint, Michigan, a Colorado middle schooler has invented a better way to test lead levels in water, as The Cut reports.

Gitanjali Rao, an 11-year-old seventh grader in Lone Tree, Colorado just won the 2017 Discovery Education 3M Young Scientist Challenge, taking home $25,000 for the water-quality testing device she invented, called Tethys.

Rao was inspired to create the device after watching Flint's water crisis unfold over the last few years. In 2014, after the city of Flint cut costs by switching water sources used for its tap water and failed to treat it properly, lead levels in the city's water skyrocketed. By 2015, researchers testing the water found that 40 percent of homes in the city had elevated lead levels in their water, and recommended the state declare Flint's water unsafe for drinking or cooking. In December of that year, the city declared a state of emergency. Researchers have found that the lead-poisoned water resulted in a "horrifyingly large" impact on fetal death rates as well as leading to a Legionnaires' disease outbreak that killed 12 people.

A close-up of the Tethys device

Rao's parents are engineers, and she watched them as they tried to test the lead in their own house, experiencing firsthand how complicated it could be. She spotted news of a cutting-edge technology for detecting hazardous substances on MIT's engineering department website (which she checks regularly just to see "if there's anything new," as ABC News reports) then set to work creating Tethys. The device works with carbon nanotube sensors to detect lead levels faster than other current techniques, sending the results to a smartphone app.

As one of 10 finalists for the Young Scientist Challenge, Rao spent the summer working with a 3M scientist to refine her device, then presented the prototype to a panel of judges from 3M and schools across the country.

The contamination crisis in Flint is still ongoing, and Rao's invention could have a significant impact. In March 2017, Flint officials cautioned that it could be as long as two more years until the city's tap water will be safe enough to drink without filtering. The state of Michigan now plans to replace water pipes leading to 18,000 households by 2020. Until then, residents using water filters could use a device like Tethys to make sure the water they're drinking is safe. Rao plans to put most of the $25,000 prize money back into her project with the hopes of making the device commercially available.

[h/t The Cut]

All images by Andy King, courtesy of the Discovery Education 3M Young Scientist Challenge.

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