Rashi (Gen. 2:23) quotes a midrash and states: "Adam mated with every [species of] domesticated animal and wild animal but his appetite was not assuaged by them, until he discovered Eve." This is, to put it mildly, a startling suggestion. While it is based on textual clues, it still offers an historical scenario that seems quite difficult to accept (note the non-literal translation in the Metsudah Rashi). In two recent articles, Dr. Eric Lawee addressed the commentarial literature on this Rashi ("From Sepharad to Ashkenaz: A Case Study in the Rashi Supercommentary Tradition" in AJS Review 30:2 ; "The reception of Rashi's 'Commentary on the Torah' in Spain: The Case of Adam's Mating with the Animals" in JQR 97:1 ).
Early Literal Approaches
As Dr. Lawee points out, there are a minority of supercommentators* who take this midrash literally while the clear majority do not. R. Yechiel of Paris, in his disputation, took it literally, and so did Chizkuni.
Early Non-Literal Approaches
However, four supercommentaries from pre-Expulsion Spain -- the glosses to Rashi (incorrectly) attributed to Ra'avad, a colleague of Profet Duran, R. Shem Tov Ibn Shaprut and R. Shmuel Almosninu -- understood it non-literally. The pseudo-Ra'avad says that the entire episode is a sod (philosophical or mystical secret), R. Shmuel Almosninu and the colleague of Profet Duran explains that Adam investigated the nature of every species, and R. Shem Tov Ibn Shaprut said that Adam's cohabitation occurred only in his intellect. R. Moshe Ibn Gabbai (in his Eved Shlomo) wrote that this midrash cannot be taken literally because the Noahide laws would have prohibited Adam from mating with animals. Rather, he studied with his intellect the natures of the animals. His son-in-law, R. Aaron Aboulrabi, wrote a supercommentary on Rashi and reached the same conclusion. R. Yitzchak Arama (in his Akedas Yitzchak), R. Yitzchak Abarbanel and R. Moshe Alshich also understood the midrash this way. So far, among the Sefardim.
Later Non-Literal Approaches
R. Yom Tov Lipman Muelhausen of Prague, the author of Sefer Nitzachon, explained Rashi's comment as meaning that Adam went out to see if any of the animals lacked a partner, and found that they did not. R. Shlomo Luria understands Rashi as explaining the midrash as meaning that Adam literally mated with the animals, but then very cautiously suggests that Rashi misunderstood the midrash and that it really means that Adam approached them "in thought". R. Chaim Ben Betzalel, the Maharal's older brother and the author of the Be'er Mayim Chaim supercommentary, understands Rashi as saying that Adam mated with the animals "in thought" to see which would be appropriate for him. The Maharal (in his Gur Aryeh and Be'er Ha-Golah) explains in his symbolic philosophical way that Adam did not mate with the animals but rather was Form looking for Matter among them. R. Mordechai Yaffe, the Levush, dismissed the Maharal's explanation as being overly philosophical and instead explained that Adam arrived at a deep understanding of each animal. R. Yissachar Ber Eilenburg, in his Tzedah La-Derekh, explained that Rashi "came upon the nature of each beast and animal in his thought, mind and intellect."
Later Literal Approaches
However, R. Eliyahu Mizrachi, in his classic supercommentary (Gen. 4:1), took Rashi literally. The Maharsha (commentary to Yevamos 63a)also took it literally, as did R. Ya'akov ben Binyamin Aharon Slonik in his Nachalas Ya'akov supercommentary. R. David Ha-Levi, the Taz, takes great pain to explain this Rashi literally in his Divrei David supercommentary.
And finally, R. Shabsai Ben Yosef Bass, the author of the Sifsei Chakhamim compendium of supercommentaries, seems to prefer the non-literal explanation of Rashi.
* A supercommentary is a commentary on a commentary.
(I had been holding onto this for months and waiting for Parashas Bereishis, but I forgot. Better late than never.)