Scientists have found that swearing most likely originates in the right hemisphere of the brain, and within that half, in the “primitive” part of the brain, the limbic system. The right half of the brain [which] is responsible for nonpropositional or automatic speech, which includes greetings, conventional expressions such as ‘not at all,’ counting, song lyrics, and swearwords. Propositional speech—words strung together in syntactically correct forms to create an original meaning—occurs in the left hemisphere.

But the evidence for this conclusion is weak, in my opinion.