Do people from indigenous cultures think as rationally as modern people?

Yes. Human beings have always been rational. People of earlier times did not think any worse than we do. They simply had less knowledge at their disposal.

The “modern man” who thinks more clearly than everyone before him does not really exist. A look at the Greek philosophers is enough. There is no thinker today who could replace Aristotle. And before him there was Socrates, who in turn speaks of even earlier thinkers. Many of them believed in God, and their reflection led them towards Him, not away from Him.

So people of earlier times were sensible people who drew sound conclusions. What was limited was only the material available to them. As knowledge grew, their minds were able to draw larger and more subtle conclusions. The same is true of people who live in simple communities today. Their minds are not lesser. Their access to knowledge is simply different.

What is remarkable is the distance between the human mind and the minds of animals. It is so vast that no bridge of small steps can be seen to explain it. Whoever reflects on this is led to God. The human mind is a special gift that all human beings have received alike. The second verse above shows that God considered every people capable of understanding His message.

One might even ask whether the mind is declining in some respects today. A mind only shines when it is committed to truth and justice. Where deception and contradiction are growing in politics, in the economy and in religion too, clever thinking does not become better but more dangerous. So there is no reason to look down on people of earlier times or on indigenous peoples.