The literature and music of a century or more ago is clearly not the work of marginally retarded minds, and its abundance indicates those who wrote it were not rare exceptions in a generally dull population. Consider genius in the past. Most people considered geniuses have IQs in the vicinity of 150, or 3 1/3 standard deviations above the mean IQ of 100. In a population with a mean IQ of 100, individuals with IQs of 150 occur with a frequency of about one in 2300 people—they're rare, but every medium-sized town has one or more, and even a small country with a population of one million has more than 425 such geniuses.
Now, in a population with a mean IQ of 70, which naïve interpretation of the Flynn effect would deem our grandparents to have had, genius-level IQs of 150 would be 5 1/3 standard deviations above the mean and occur, on average, in only one out of 20,396,324 people. If we take the Flynn effect as 3 IQ points per decade, then we'd expect a mean IQ of 70 around the year 1900. In 1900, the world population was about 1.7 thousand million, which would imply there were only 80 people with genius-level IQs in the entire world of 1900. The merest glance at the history of that era will reveal how ridiculous a supposition this is.
For the “Flynn effect” ideas and thoughts here is a link to the drop in IQ - Global IQ: 1950–2050
