If you mean “why do we laugh”
It is hypothesized that laughter developed in great apes as a way to diffuse socially tense situations. As our ancestors became more social and living in groups, it became more crucial to be able handle social problems even before speech developed. Laughter is believed to be a way individuals can acknowledge and try to move past an embarrassing or tense situation. Laughing together also builds bonds.
If you mean “what are the mechanical/chemical systems that happen in our bodies to create laugher” I haven’t the slightest clue.
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