The Flynn effect — where tested intelligence increased over past generations due to better health and more education — is said to be slowing.

Of course, such findings are difficult to assess because they are subject to value judgments. But David Robson, author of The Intelligence Trap: Why smart people make dumb mistakes (2019), offers some useful observations, including asking what does the Flynn effect really measure?:

James Flynn himself has argued that it is probably confined to some specific reasoning skills. In the same way that different physical exercises may build different muscles – without increasing overall “fitness” – we have been exercising certain kinds of abstract thinking, but that hasn’t necessarily improved all cognitive skills equally. And some of those other, less well-cultivated, abilities could be essential for improving the world in the future…

You might assume that the more intelligent you are, the more rational you are, but it’s not quite this simple. While a higher IQ correlates with skills such as numeracy, which is essential to understanding probabilities and weighing up risks, there are still many elements of rational decision making that cannot be accounted for by a lack of intelligence.

Consider the abundant literature on our cognitive biases. Something that is presented as “95% fat-free” sounds healthier than “5% fat”, for instance – a phenomenon known as the framing bias. It is now clear that a high IQ does little to help you avoid this kind of flaw, meaning that even the smartest people can be swayed by misleading messages.

David Robson, “Has humanity reached ‘peak intelligence’?” at BBC Future (July 9, 2019)

Apparently, intelligence does not cause us to be less influenced by cognitive biases like these:

• temporal discounting — We grab short-term gains in place of long-term benefits. For example, we insist on a particular new traffic control system because it is popular (thus we are popular too) when a different new system would perform better over the long run (but requires long-term investment).
• confirmation bias — In a pro vs. con discussion, we pay more attention to evidence that supports our current views than evidence that doesn’t. We don’t even look for evidence that tests our views. For example, if we already believe that the popular new traffic control system is a must, we focus on the traffic studies that support our views and ignore the ones that do not.
• sunk cost bias — We continue to invest in something that is clearly failing because facing reality after all this time is just too painful. For example, we continue to support the new traffic control system even though it has multiplied our traffic problems because, by now, the lesson is too much of a wallop to our egos.

Robson says, general critical thinking skills don’t necessarily improve with IQ either,

Besides a resistance to these kinds of biases, there are also more general critical thinking skills – such as the capacity to challenge your assumptions, identify missing information, and look for alternative explanations for events before drawing conclusions. These are crucial to good thinking, but they do not correlate very strongly with IQ, and do not necessarily come with higher education. One study in the USA found almost no improvement in critical thinking throughout many people’s degrees.

David Robson, “Has humanity reached ‘peak intelligence’?” at BBC Future (July 9, 2019)

If so, even if the Flynn effect continued, it wouldn’t necessarily lead to better decision-making or a better society. Conversely, if it stalls or reverses itself, the outcome might not necessarily be a worse one. The key factor here is wisdom, not intelligence. Wisdom causes us to reflect on our choices; intelligence only enables us to, say, build better spacecraft so that we are making the same (maybe bad) decisions in outer space instead of at home.

And wisdom is one of those things, like human consciousness, whose existence we can observe — but truly explaining them is very hard. So, even if we have reached “peak intelligence,” it might not matter as much as we think.

New Zealand-based James Flynn, originator of the Flynn effect, believes that “environmental factors play a greater role in intelligence than genetics does.”

It’s called the “Flynn effect” — the fact that each generation scores higher on an IQ test than the generation before it. Are we actually getting smarter, or just thinking differently? In this fast-paced spin through the cognitive history of the 20th century, moral philosopher James Flynn suggests that changes in the way we think have had surprising (and not always positive) consequences. (March 2013)

In any event, it does not follow that a continually improving environment would mean a continuing increase in intelligence. Everything in this frame of reality has its limits.

You may also wish to read: Is the octopus a “second genesis” of intelligence? Can its strange powers provide insights for robotics or the human mind?

and

The real reason why only human beings speak. Language is a tool for abstract thinking—a necessary tool for abstraction—and humans are the only animals who think abstractly