The idea that a person's smile remains the same throughout their life is an overly simplistic view of the development of facial expressions. While it is true that there can be certain underlying features of a person's smile that remain the same, there is a significant amount of variation that occurs over the course of someone's life.
First, the physical shape of someone's mouth and teeth can change over time. As we age, our teeth may yellow, chip, or fall out altogether, altering our smile's appearance. In addition, our facial muscles can lose elasticity, making our smiles appear less vibrant than they were when we were younger.
Second, our smiles can also be affected by our emotional state. People's smiles tend to be different when they are feeling happy versus when they are feeling sad or angry. It is quite possible for someone to have a different expression when smiling in their early childhood compared to when they are older.
Finally, our environment can also play a role in how we express ourselves. Growing up in a different culture or environment can lead to different expressions of joy and happiness, which can be reflected in a person's smile.
In conclusion, it is evident that a person's smile can change over the course of their life, so it is inaccurate to state that it remains unchanged. One's smile can vary depending on the physical changes of their mouth, their emotional state, and their environment.
