Depends on how far back you go. For a Roman, mental multiplication was exceedingly difficult. Clearly this implies that there was a period of upward trend. If we believe that we're dumber than some of our forefathers, then there must have been a peak at some point in the past (or perhaps even multiple peaks, but we don't have enough evidence to suspect more than one, so let's assume it's an approximately parabolic trajectory).

Obviously, it was the men and women of the 1950s, who built computers and airplanes from nothing with little more than their wit, a grease pencil, and some twine, who were of the utmost in mental capacity and grit.

Since we're only 60 years from 1950, whereas 1869 is 81, we must be smarter than them. In fact, we're about as smart as people were in 1890. Ten years ago, we were as smart as people in 1900, but sadly such intelligence is ten years gone.

A corollary: in another 21 years, people will look back at this exam and just barely understand it. A few years after that, all hope is lost.