One line of evidence is that all the names in the genealogies prior to Babel have meanings in Hebrew.
My first Hebrew professor, Dr. Robert L. Cate, did a lot of work in the development of the Hebrew language. For his doctoral dissertation, he constructed a hypothetical lexicon of proto-Hebrew, the Hebrew language as it existed before any written records. There are clues within the language as it existed in the written Bible times of what it looked like before.
Dr. Cate concentrated on how the verbs had formed. In Biblical Hebrew, all verbs have three consonants at the root. He found evidence of a two consonant root system underneath it. Many verbs that shared two consonants in their ground form (Qal, perfect, 3ms) and in the same order, would have related meanings. For example, bara' means "create," barak means "bless," and barar means "purify." All of those are primarily actions of God (in the case of "create," only God can truly create).
He gives many more examples, but I don't think his dissertation was ever made available online.