Without cherry-picking extreme examples too much, thalidomide was used as a drug to treat morning sickness, and pregnant women who were taking it were sometimes giving birth to children who did not have arms or legs.

A number of things have been found to be incorrect over time.

Where once, being transgender was viewed as a mental illness, nowadays, it is recognised differently. I say that the true determinant of a person's gender is what's between their ears not between their legs.