Question

The following question was once posed to me: Based on the Gemara in Brochos 35a which says that we don't make a blessing on olive oil because it's a mazik, what happens if science proves that it's not a mazik? I don't remember the answer given, but he did mention that Chazal can be wrong. Is this true? I asked somebody else and they answered: If Chazal argue with each other, they cannot both be correct. Either one is right and one wrong, or both are wrong, but they cannot both be right if they are in opposition. Therefore, Chazal are fallible as all humans are. Even Moses made mistakes. For some reason or another, though, that doesn't sound right.

Answer

It is not a matter of right and wrong, it is a matter of times that have changed, and nature has changed. There are mutations of olives, and other plants, which causes size and taste to change. Chemicals, age, environment and many other factors have an effect on humans, animals and plants.

This idea of change applies to many Halachic concepts -- e.g. the list of Treifot (animal diseases), the size of an olive and egg (regarding how much matzah to eat on Passover, for example), and many other applications. (source: "Chatam Soffer" O.C. 181; "Igrot Moshe" Y.D. I 2,215; II 74, 146)