Why do some people get dimples?

Cheek dimples are caused by the facial muscles called zygomaticus major. It connects the corners of our mouth to the face. When we are happy, the zygomatic muscles contracts and pulls the skin. However, in some cases, this long continuous muscle divides into two bundles. One is connected to the upper lips and other end is connected to our lower jaw and when we laugh, these bundles contracts and causes dimple on our cheeks. However the Chin dimples are occur because the two jaw bones in the chin failed to fuse during the embryonic development.