Considering that people with IQs below 70 are today considered to be suffering from an "intellectual disability" that's a remarkable claim.* (Jargon watch: The intellectually disabled used to be called mentally retarded and before that they were called moronic.) So if these data are right, chances are that your great grandparents were morons. However, as New Zealand political scientist James Flynn points out in his new book, Are We Getting Smarter?: Rising IQ in the 21st Century, average IQs have been going up at the rate of about 3 points per decade over the past century. Flynn identified this ubiquitous trend (now named the Flynn Effect) back in the 1980s when he realized that the regular renorming of IQ tests suggested that an American with an average IQ of 100 today would score 115 on a 1950s IQ test. 

In today's New York Times, columnist Nicholas Kristof summarizes Flynn's findings this way:

The average American I.Q. has been rising steadily by 3 points a decade. Spaniards gained 19 points over 28 years, and the Dutch 20 points over 30 years. Kenyan children gained nearly 1 point a year.

Those figures come from a new book by Flynn from Cambridge University Press called “Are We Getting Smarter?” It’s an uplifting tale, a reminder that human capacity is on the upswing. The implication is that there are potential Einsteins now working as subsistence farmers in Congo or dropping out of high school in Mississippi who, with help, could become actual Einsteins.

The Flynn Effect should upend some of the smugness among those who have historically done well in global I.Q. standings. For example, while there is still a race gap, black Americans are catching up — and now do significantly better than white Americans of the “greatest generation” did in the 1940s...

Flynn argues that I.Q. is rising because in industrialized societies we give our brains a constant mental workout that builds up what we might call our brain sinews...

But Flynn argues that modern TV shows and other entertainment can be cognitively demanding, and video games like those of the Grand Theft Auto series probably require more thought than solitaire.

In my column, "Are Smart Countries Richer or Are Rich Countries Smarter?," I reported some of the findings of American Conservative publisher Ron Unz that explored how the Flynn Effect has long been boosting the intelligence of various immigrant groups so that many now score higher IQ averages than the IQ average of "old stock" Americans. Among other things, Unz attributes rising IQs to the salutary effects on intellectual development of increased urbanization.

In addition, a Wired article last year pointed out that the smartest are also getting smarter over time. Surely, if you're reading Reason, it would suggest that your IQ score is at least two deviations above the current median, right?

*Perhaps this explains why some segments of the population were so stupidly attracted to Communism and Nazism in the early 20th century.