A cleft chin is also called a dimple in the chin, a chin cleft or even less elegantly termed a butt chin. It is a small to large indentation in the chin that is actually genetically determined and is caused by failure of the lower jawbone to completely fuse together at the center point. This doesn’t cause problems for most people with a cleft chin; it merely causes variance in appearance. You’ll often see that parents with cleft chins tend to produce children with the same marking. Cleft-chinned parents may or may not pass along the trait to their children, and some children will be born with cleft chins to parents without the trait.
The cleft chin is an interesting study and example of how genetics can work, and how inherited genes sometimes fail in expression. Theoretically, parents who both have cleft chins would immediately pass this on to children, since it is a dominant trait. There are two reasons why this might not occur, because genes dictating the cleft can be affected by variable penetrance. Variable penetrance means that even a dominant trait may not be expressed. This may be caused by the environment — something in the fetal environment caused the jawbone to fuse completely. It also may be caused by something called modifier genes, which affect the function of the genes responsible for the cleft chin.
If the modifier genes suppress the gene controlling incomplete fusion of the jawbone, then the cleft would not be expressed. Alternately, two parents without cleft chins may both have had modifier genes, resulting in jawbone fusion. Their children might lack these modifiers and all have clefts despite that fact. The point is, whether or not parents have clefts, children may or may not have them. Variable penetrance can cause a little confusion, but explains why the cleft isn’t always inherited, or may appear among children whose parents don’t have clefts, though this is rare.
Cleft chins have certainly existed for a very long time. Homo sapiens fossilized remains discovered in France in the caves of Isturitz are carbon-dated back tens of thousands of years and show prominent clefts. The cleft chin also predominates in literature.
Villains often have deep clefts, and so do heroes. We also love our current and past actors with cleft chins, such as Cary Grant, Kirk Douglas, Michael Douglas, John Travolta, Jude Law, and Sir Ian McKellen. It should be noted that many of these actors have played both villains and heroes, and the cleft chin seems to be one of those adaptable facial traits that can lend itself to dramatic expression in different ways.