"If you see or hear someone being lenient and pronouncing it kosher… do not listen to him, do not be drawn to him and let there not be something like this in Israel. Anyone who proclaims such a thing to be kosher appears in my eyes as someone who is raising suspicion on the words of the Sages. I am writing at length on this matter so that a line should be drawn for you and for everyone that fears and trembles at the word of God – and the sanctified words of the Sages of Israel should not become as a broken fence for every fox to breach! …That which the Sages listed in these principles can never, under any circumstances, become permitted… And since this is so, even if many were to come and say that they have seen [animals with these defects living longer than twelve months] we would deny it, such that the words of the Sages should be established, and we should not raise suspicions on the Sages’ words by establishing the words of these people… Let this person testifying and a thousand like him be invalidated, rather than invalidating a single thing from that with the holy Sages of Israel have agreed upon, the prophets and the descendants of prophets, and the words that were spoken to Moses at Sinai… the conclusion of the matter is that it is better to chase after arguments in order to establish [the Sages’] words rather than to dispel their holy, true and established words in favor of establishing the empty words of these people… Everyone needs to preserve the principles that are transmitted through the People of Israel--and even if all the winds in the world were to blow, they will not move us from this place." (Responsa 1:98)
Even though the testimony of two witnesses is considered extremely powerful in Jewish law, Rashba insists that that we would dismiss the testimony of a thousand witnesses who claim to have seen an animal with one of these defects living for more than a year.
Seven hundred years later, however, Rav Moshe Feinstein wrote the following remarkable words:
"…even the Rashba, were he to be alive today, and likewise now that he is in the World of Truth in Gan Eden, would agree that some of those listed in the Mishnah and Talmud as being tereifos are, in fact, able to survive…" (Igros Moshe, Choshen Mishpat vol. II 73:4, p. 308)
This is a remarkable development! The Rashba insisted that all evidence to the contrary must be dismissed, if necessary by way of "chasing after" arguments (i.e. contriving forced arguments). But seven hundred years later, Rav Moshe says that it's just not possible. The evidence is too strong. (Rav Moshe continues to state that Chazal's laws still stand regardless, for reasons that I have discussed in Sacred Monsters.)
There is another, similar, change that took place in a different area of halachah. In the eighteenth century, there was widespread fear that people were being buried alive due to their being mistakenly diagnosed as dead before they had actually expired. Many physicians of that era insisted that cessation of breathing does not suffice and that a thorough medical examination was required. A question arose as to whether a kohen could be the doctor to examine a corpse and certify that death had taken place. R. Tzvi Hirsch Chajes ruled that it was permissible, arguing that the absence of respiration did not conclusively mean that the person was dead and thus the doctor could potentially be saving a life. Chasam Sofer, on the other hand, firmly opposed the idea that a person who was not breathing could be considered even possibly alive:
"When respiration has ceased, one does not further violate Shabbos (in a rescue attempt); and this is necessarily a rule for all deaths, for it is the definition which is accepted in our hands from the time that we became a congregation of God and a holy nation. And even if all the winds in the world were to blow against us, they would not budge us from the position of our holy Torah." (Responsa Chasam Sofer, Yoreh De’ah #338)
This time, it only took two hundred years for the winds to budge us. As Rav Shlomo Zalman pointed out, the cessation of respiration should no longer be used to determine death, since it can be reversed:
"With regard to the fundamental words of Chasam Sofer, in my humble opinion it appears that just as with regard to the law that an eight-month fetus is like a stone and one does not transgress Shabbos on its behalf, certainly the rule has changed in our time, and forfend to rule in that way (of the Gemara)… and one is forced to say that only in the times of Chazal was the fetus given the status of a stone, because at that time they did not know how to enable it to survive, unlike in our time… So, too, in my humble opinion it appears clear that in our time, it is impossible to decide that someone as already died except via the latest techniques which establish the boundaries between life and death. And forfend to rely in our time just on the signs of breathing and suchlike, more than other checks, and to rule with someone under a collapsed building on Shabbos that if his breathing has stopped, and his heart has stopped beating, that he should be left under the rubble and Shabbos not be transgressed on his behalf…" (Shulchan Shlomo, vol. II, pp. 34-35)
Of course, irreversible cessation of breathing can still be used to determine death; but that is not what Chassam Sofer was saying. He was saying that all cessation of breathing is by definition irreversible. (See this post for further discussion regarding his view.)
And so we have two of the most famous and powerful rabbinic statements against accepting the scientific advances of their era, both dramatically claiming that all the winds in the world would not change their position. And in both cases, later rabbinic authorities acknowledged that the winds really have blown very strongly indeed, and that the counter-evidence can no longer be rejected.
There's a lesson here...