Why do we laugh? We laugh when someone cracks a joke. But what is it that actually brings laughing when some jokes a lot? Apart from laughing, we smile. If so what is smile?
From the evolutionary biology point of view, laughing and smiling are two completely different reactions to different situations. Smiling is basically used as a tool for communication when we are not intended to have elaborated talking. Smiling is observed in children from 6 weeks of their birth so as to identify the unknown person’s response. Children on seeing any one first put a friendly smile on their tender lips and observe the reply from the other. If the stranger smiles back at him then the child will be in comfortable situation. Children also smile to communicate with their well known to greet or welcome them. Hence smile is evolved on human faces as one of the finest way of communication when speech is not active. We smile when we are expressing positive emotions and the positive emotions are differing from individuals including the associated facial muscular actions in wide variety. As such the actual neurobiological sequence of reactions occurring in the brain for the cause of smile is still unknown. Not only humans but animals also smile or even laugh, exposing their teeth differently in different situations. Even humans also smile at animals when they greet or affectionately tame them. Hence smile is ultimately evolved as a universal facial expression.
What is laughing? Laughter is the involuntary audible reaction to adjust our psyche when an unexpected situation is experienced. But the unexpected situation should be on the lighter vein than painful. For example we laugh when any one slips down before us. But if the man is seriously injured with blood due to slipping then we do not laugh but we will be in hurry to save him. That means laughter is the resultant reaction to adjust our psyche for sudden unusual or surprising harmless actions we witness. Joke is something that puts us in confusion and surprising state momentarily due to incoherence of the jovial situation with preoccupied logic in the brain. Hence our body immediately reacts as laughter to relieve our psyche from the disturbed situation. It is found that laughter improves our mental health and makes us feel comfortable. This is because of the release of endorphins during laughing in our body due to activation of prefrontal cortex and also the involvement of the limbic system (the seat of emotions) in the brain. The laughter can also be caused due to severe disturbance to the psyche and this is generally observed in mad people. Laughter can also be caused due to stimulation of relevant nerve cells in the brain by injecting substances externally, for example, the nitrous oxide, commonly known as the laughing gas. But such methods are found to be deleterious. Besides this, laughter is sometimes contagious. If any one sees a person laughing unusually, it provokes him to laugh. This is because of the same reason. On seeing the unusual laughing of the other person, the person is thrown into the sudden confusion or illogical state and reacts to it by laughter. But if the laughter results in too much non sense, then the observed person may also be annoyed! Apart from this, laughter is known as best medicine and is made to practice regularly in some yoga classes as a part of exercise. Surprisingly, this is not done by cracking jokes, but, the participants are made to laugh voluntarily and loudly. This comforts the movement of facial muscles and dilates the blood vessels facilitating the free flow of blood thus aids in having good health.