Did you know humans are the only animals to have chins? They come in all shapes and sizes, but the most obvious difference from one chin to the next is whether they have a cleft or not. In those with a chin cleft, it can be very pronounced. Or it can be much more subtle, appearing simply as a small chin dimple.

Chin Cleft Development

The shape of your chin is determined before you're born. When a fetus develops, its jawbone starts growing on both sides of the head and meets in the middle of the chin.

In people who have a chin cleft, the two sides of the lower jaw don't completely fuse together, leaving a little space, or a cleft.

Clefts come in various shapes, from a vertical or Y-shaped crease to a round dimple.

The presence and shape of a cleft is only known to be cosmetic. As the chin serves no specific biological function, having a cleft or not has no impact on your everyday life aside from impacting your looks.

The Inheritance of a Cleft Chin

The genetics behind cleft chins used to be thought of as simple. Cleft chins were believed to be a dominant trait: if two parents had cleft chins, their kids could have a cleft or might not. And if two parents had smooth chins, their kids would always have smooth chins.

It's still more likely than not that if your parents both have cleft chins, you'll have one. And if both have smooth chins, you will too.

But it turns out a cleft chin is too complicated to be simply "dominant." Two parents without a cleft have kids with cleft chins way more often than predicted with this simple model.

The Science Behind Cleft Chins

The science behind cleft chins is complicated enough that no one can predict with 100% confidence whether someone will have a cleft chin or not—even if we look at all of their DNA. A further challenge to predicting cleft chins is that scientists have yet to study the human genetics of chin shape extensively. So there's still a lot they don't know.

AncestryDNA^® tests over 8,000 genetic markers identified by Ancestry^® scientists as associated with the cleft chin trait. But this is by no means the whole story. Lots of other parts of your DNA, as well as environmental factors, play a role in whether or not you will have a cleft chin too. Scientists evaluate the impact of genetic versus environmental influences on a trait with a measure called "heritability."

Fun Facts About Cleft Chins

We're all born with our chin shapes. That means everyone you know with cleft chins—and Hollywood legends like Rock Hudson, Kirk Douglas, and Humphrey Bogart—all had their chin clefts as babies. Later in life, as faces become thinner, cleft chins do in fact become more prominent.

Research suggests women with cleft chins are slightly less common than men with cleft chins. This may be why even today when you think of celebrities with cleft chins, you might tend to first think of actors like Ben Affleck or John Travolta, rather than Sandra Bullock or Blake Lively.

References

Cherney, Kristeen. "Cleft chin surgery: What is a cleft chin?" Healthline. September 18, 2018. https://www.healthline.com/health/cleft-chin.

"Dimple-Chinned Actors." IMDb. February 1, 2015. https://www.imdb.com/list/ls000237021/.

McDonald, John H. "Cleft chin: the myth." Myths of Human Genetics. December 8, 2011. https://udel.edu/~mcdonald/mythcleftchin.html.

Pickrell, Joseph K, Tomaz Berisa, Jimmy Z Liu, et al. "Detection and interpretation of shared genetic influences on 42 human traits." Nature Genetics. May 16 , 2016. https://www.nature.com/articles/ng.3570.

Razzaq Rabia, Safoora Kanwal, Shandana, et al. "Tongue rolling, folding, cheek dimple and chin cleft; study of morphogenetic traits in Quetta population." World Journal of Zoology. 2015. DOI:10.5829/idosi.wjz.2015.10.3.95205.

Yong, Ed. "We're the Only Animals With Chins, and No One Knows Why." The Atlantic. January 28, 2016. https://www.theatlantic.com/science/archive/2016/01/were-the-only-animals-with-chins-and-no-one-knows-why/431625/.