Engraven on your countenance

Do you realize that what you do affects how you look? There are the obvious examples of eating unhealthy food making you fat, or exercising to build muscle, or not getting enough sleep gives you bags under your eyes. Do you think it also works on the non-obvious actions we take? Does committing sin or following the commandments actually affect your countenance? Apparently it does!
Some researchers at Cornell performed a couple of experiments on the subject. They compiled similar photos of people, half of which were convicts, and half of those were for violent crimes. They then asked people to rate whether they thought the person had committed a crime and whether it was violent or not. They found a significant effect that people were able to identify the criminals based solely on their face. The people who thought they could identify the pictures as mug shots did worse than those who just went with their gut instinct. They only speculate on the correlation vs causation issue. But based on experience and knowledge of the gospel, I would lean toward the causation side of the argument. They recommend following your gut instinct when you see people and get a bad vibe. Somehow you know something is off, and your self-preservation instincts kick in.

The idea is also explored in Oscar Wilde's "The Picture of Dorian Gray," where a young nobleman (Dorian) has a picture drawn of himself. The man engages in a life of sin, but the picture takes the effects of the sin rather than the man. When Dorian sees the picture as a glimpse into his soul, he goes into a rage and later drives a knife into the picture, which breaks the spell and reverses the roles. The picture shows him as he once was before the life of sin, and he has the knife in his disfigured, wrinkled body. So the concept of sin affecting your countenance has been around for a while.
Well, I guess it goes back a little longer. In speaking of the sins that Judah and Jerusalem will commit, "the shew of their countenance doth witness against them; and they declare their sin as Sodom, they hide it not." (Isa. 3:9) On the other hand, a life of righteousness will show on your countenance as well. Alma told the people of Zerahemla that "I say unto you, can you look up, having the image of God engraven upon your countenances?" 
When you think no one will find out, it becomes much easier to commit sin. Knowing that there is an actual change in your appearance that is detectable by others might change that. Scientists cannot yet determine exactly what changes in our countenance, but something does change and people somehow know it at a sub-conscious level. I imagine that God knows this change perfectly. Somehow all of our actions are engraven on our souls and will be detectable at the judgement day. Its kind of scary to think about it, but it can also help inspire us to do better. Elder Oaks said "The Final Judgment is not just an evaluation of a sum total of good and evil acts—what we have done. It is an acknowledgment of the final effect of our acts and thoughts—what we have become."  Our actions help define what we are, and what we are is how we are judged at a gut instinct level by others and ultimately by God at the last day.