Rambam, Mishneh Torah, Shechitah 10:12-13

The following, except for the Hebrew, is from a comment I have posted to Lakewood Yid's blog article at http://lakewoodyid.blogspot.com/2006/09/rambam-ignore-evidence.html.

הלכות שחיטה פרק י

יב ואין להוסיף על טריפות אלו, כלל: שכל שיארע לבהמה או לחיה או לעוף חוץ מאלו שמנו חכמי הדורות הראשונים, והסכימו עליהן בתי דיני ישראל--אפשר שתחיה. ואפילו נודע לנו מדרך הרפואה, שאין סופה לחיות. יג וכן אלו שמנו ואמרו שהן טריפה--אף על פי שייראה בדרכי הרפואה שבידינו שמקצתן אינן ממיתין, ואפשר שתחיה מהן, אין לך אלא מה שמנו חכמים, שנאמר "על פי התורה אשר יורוך:

This Rambam says the following to me: Chazal wouldn't have said an animal can live with a certain injury unless they had reason to think it could - presumably meaning evidence that an animal with such an injury had indeed lived. Therefore, even if we can't explain it, we have to go with their empirical evidence.

However, it's much harder to understand how we could be witnessing a tereifah live more than a year. Maybe we're not so good at keeping non-tereifot alive, and so even though Chazal could sustain them for a year or more, we can't. But how do we explain a tereifah that lives beyond a year? Chazal couldn't sustain the animal, but we can?

Rambam's implicit answer is that this is indeed the case, but hilchot tereifot are nonetheless already etched in stone (perhaps because the 2000 years of Torah that the Chazon Ish spoke of have ended), and so, "Ein lecha ela mah shemanu chachamim." The halacha they established is permanent, as per "Al pi hatorah asher yorucha."

That doesn't, however, mean their science was right. Just as Rabbi Eliezer was theoretically right in the case of tanur achnai, but the halacha nonetheless follows Rabbi Yehoshua, so too in this case certain animals may really - medically speaking - not be tereifot, but since they have been established as tereifot by the halachic process, they are halachically tereifot, period.