Still not understanding how #3 is not an argument. If linguists are doing comparative analyses of traditional languages, there is a reasonable “assumption” that there are languages across multiple eras and cultures. That definitely supports human communication being universal. It’s a horrid argument, don’t get me wrong. It doesn’t prove that all cultures and eras everywhere have have language, and it is after all based on an assumption. But it still supports the conclusion. It’s truthfulness does make communication universality more true, as LACK of comparative analyses would strengthen the idea that human communication is NOT universal.