"And the man knew Eve his wife" (Genesis 4:1). No creature had relations before Adam the first man. It is not written here "and he knew," but rather "and the man knew" - he made known to all the way of the world [the manner of human relations]. Another interpretation. "He knew" from what tranquility he had been removed. He made known what the serpent had done to him.
Adam Knew Eve and Made the Way of the World Known
Yalkut Shimoni on Torah 35:1
(בראשית ד א) וְהָאָדָם יָדַע אֶת חַוָּה אִשְׁתּוֹ, לֹא שִׁמְּשָׁה בְּרִיָּה קֹדֶם לְאָדָם הָרִאשׁוֹן, וְהוּא יָדַע אֵין כְּתִיב כָּאן, אֶלָּא וְהָאָדָם יָדַע הוֹדִיעַ לַכֹּל דֶּרֶךְ אֶרֶץ.