All languages share some common features at their core, but they also differ in things like pronunciation and word order. The document discusses three hypotheses for why languages share universals: that all languages descended from a single protolanguage (monogenesis), that they influence each other through language contact, and that linguistic abilities are innate to humans (innateness). It provides examples of both absolute universals found in all languages, like the distinction between vowels and consonants, as well as statistical universals that are predominant but not universal, like subjects tending to precede objects.