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Dimples! They're so cute, but surprisingly mysterious! What causes them naturally and how can we make them happen?

Hosted by: Hank Green
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Sources:
https://www.google.com/patents/US2091276
https://link.springer.com/article/10.1007/BF02449856
http://onlinelibrary.wiley.com/doi/10.1002/ajmg.1320360337/full
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2238342/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3385407/
https://www.ncbi.nlm.nih.gov/pubmed/9810983
https://www.ncbi.nlm.nih.gov/pubmed/9725574
https://www.ncbi.nlm.nih.gov/pubmed/24317251
https://www.ncbi.nlm.nih.gov/pubmed/7958797
http://udel.edu/~mcdonald/mythdimples.html
http://omim.org/entry/126100

Images:
https://commons.wikimedia.org/wiki/File:Buccinator_muscle_lateral.png
https://commons.wikimedia.org/wiki/File:Sobo_1909_260_-_Zygomaticus_major_muscle.png
https://en.wikipedia.org/wiki/Joseph_Gordon-Levitt#/media/File:Joseph_Gordon-Levitt_Mar_2009.jpg
https://commons.wikimedia.org/wiki/File:AdamLevine2011.jpg
Hank: Dimples! We tend to think of them as cute or attractive... I mean, can you picture Joseph Gordon Levitt without them?! But considering how coveted these facial features can be, we know surprisingly little about them.

Cheek dimples aren’t exactly at the top of many researchers’ priority lists, which I suppose is how it should be. But we’re not even quite sure what they are. And if you think they’re inherited, well... yes, but not necessarily the way you think.

We do know that they’re fairly common. Studies in different populations have found that anywhere between 10 and 40 percent of people have dimples. As for why you, your friend, or yes, Adam Levine, have these adorable features, anatomical studies suggest that it has to do with a variation in a muscle of the face called the zygomaticus major.

This funny-sounding muscle is indeed that -- it helps us smile! It connects the corners of the mouth to the cheek bones just under the eyes. When we’re feeling happy, or just faking it, that muscle contracts, pulling the corners of the mouth upward into a big grin.

But sometimes, instead of staying as one, continuous muscle all the way from the cheekbone, the zygomaticus major splits into two, and attaches in two spots, with one part connecting to the usual spot just above the corner of the mouth, and the other attaching slightly below. This variation is called a bifid. When this happens, the lower section also sometimes connects to some cheek skin. So, when bifid zygomaticus major muscles contract, it’s thought that the lower part pulls on that skin, causing it to buckle, creating a dimple.

But it’s hard to say for sure that the bifid muscle is the reason people have dimples, because the anatomical studies that have looked into this question were done on cadavers, and they’re not exactly doing a bunch of smiling at that point.

Dimples are also somewhat confusing when it comes to how they might be inherited. They’re often touted as an example of a dominant genetic trait, where a child has a 50 to 100% chance of having dimples if one of their parents does. Sometimes, dimples are even used in classrooms when teaching about genetics. Few studies have actually been done on the heritability of dimples.

One study, done in Russia in the 1990s, looked at 75 families for a variety of physical traits, including the presence of cheek dimples. The results suggested that dimples were a dominant trait controlled by one gene, but researchers also noticed that inheritance changed depending on whether a person was male or female.

More recently, the gene-profiling company 23andMe did its own investigation into dimple genetics, which found that dimples were associated with nine different genes. Complicating matters even more is the fact that dimples can come and go over time. In some people, dimples only show up in adulthood. While in others, those cute divots only show up when they’re children.

So, dimples could still be largely genetic, but these patterns suggest multiple genes could be involved, and that environmental factors matter, too. For instance, whether dimples show up could be related to the amount of fat in the face, or the elasticity in the skin, both of which could be tied to age or sex.

And of course, these days not everyone who you think has dimples has them naturally. Some people get dimple piercings to get that look, or resort to cosmetic surgery. Even though we don’t have a great sense of what a natural dimple is, plastic surgeons have figured out how to make them in the operating room.

One procedure attaches skin to the underlying muscles. But instead of using zygomaticus major, surgeons tether skin to the buccinator muscle, which is one of the key cheek muscles that helps you chew food. Alas, this technique isn’t always permanent, and the dimples can fade. But if you really want the dimples, at least you’ve got options.

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