I get what you're saying and it doesn't make a material difference, but a lifespan and a generation are quite different. My grandpa was born in 1928, when peni

I get what you're saying and it doesn't make a material difference, but a lifespan and a generation are quite different. My grandpa was born in 1928, when penicillin was discovered. There's a picture of him holding my brother's grandson. That's five generations in one lifespan, four of which could have been meaningfully impacted by the availability of a general antibiotic. Now are we going to start observing the influence of that on the human immune system in four generations? No. Forty? Maybe a little bump in the noise floor. Four hundred? Almost certainly yes.