Depends what we call 'intelligence'. As far as I know intelligence is remarkably difficult to adjust upwards in the technical sense. But, practically, we can train young people not to do stupid things so they will act more intelligently in the common sense of the word.
One fun example might be the anti-usury stance of the Catholics back in the (I'm told) the 12th century. A society that can't charge interest on its debts is a society where people will behave stupidly compared to a society where people can lend money profitably - people will just walk by situations that they can identify as big win-win scenarios and rationally not pursue them. But it isn't linked to individual intelligence as much as how what people are raised to believe.
When you were a farmer with a failed harvest, that loan wasn't a win-win, it was a debt trap, because economic growth was hard to come by. In today's fossil fuel powered society, growth is much easier to come by, so the advantages are downright obvious.
That doesn't seem like an easy position to defend. In the pre-modern era, the baselines are so small that a 5% growth rate was possible to achieve with even primitive tools. And a smart person could found entire fields of science with a decade of study of common phenomenon. The world was rich with growth opportunities.
It'd have been much easier to grow if they'd had social structures that allowed it. The lawmakers at the time just didn't realise how much damage inefficient and poorly organised financial and property systems were doing to the general wellbeing.
If nothing else, well developed structures around loans would make it easier for the early societies to discover that fossil fuel was a huge source of growth.
In the context of loans, though? The point of a loan is to enable someone to do something they couldn't do under normal economic constraints.
Crop failure could be a matter of literal life and death. I can imagine the most forward-thinking community in a country coming together and funding the smartest guy they've ever heard of to figure out how to stop that. Or any of a number of other growth areas.
One fun example might be the anti-usury stance of the Catholics back in the (I'm told) the 12th century. A society that can't charge interest on its debts is a society where people will behave stupidly compared to a society where people can lend money profitably - people will just walk by situations that they can identify as big win-win scenarios and rationally not pursue them. But it isn't linked to individual intelligence as much as how what people are raised to believe.