The issue with your idea is that there is no way for the tribe to be able to parse between what we would consider obvious supernatural explanations and physical ones. The reason that humanism became popular is because of the advent of technology that allowed us to prove and disprove certain beliefs. God stopping the sun in Joshua makes no sense in a universe that runs on heliocentricity. Spontaneous generation makes no sense when you can isolate and sterilize something see that nothing grows on it. In a world where you only have Stone Age hunter-gatherer technology, how do you know that a volcano erupting or lightning striking isn't because some god or spirit did it? How can you prove otherwise? There's no way to test either Oog's hypothesis that Vulcan did it or Ugh's hypothesis that it was due to natural processes deep below the Earth's crust.

The thing is ancient people weren't stupid. Their beliefs in gods and spirits really were things that made logical sense to them. And in many cases the beliefs did have actual reasons behind them, they worked but not for the reasons that ancient people believed. For example the Chinese Mandate of Heaven may seem silly until you realize that widespread famine and disaster can easily be caused by governmental mismanagement instead of divine providence, and it could be taken as a sign the government is incompetent and must be deposed.

In many cases their beliefs became outdated and you had people desperately holding onto them through faith alone, but the original reason they were adopted was not because they were stupid. It was merely because they didn't have a complete understanding of the phenomenon. And to be honest more recent scientists aren't much better, what with historical researchers believing all sorts of dumb ideas that don't make it into the science textbooks (e.g., Newton and his mysticism).

Another question you have to ask is what purpose does this behavior serve? The scientific method became popular mostly among Western aristocrats who had enough resources and time that they could afford to sit down and run repetitive experiments to rule out all possible alternatives, or sit on their butt theorizing and writing equations. For a Stone Age society that is more concerned about day to day survival and is working a lot of the time, and who does not have a need for complex mathematics or have access to things like paper or parchment, what good does this behavior serve? In terms of day to day survival, the superstitious person will do just as well (if not better, due to higher caution) than the humanistic one.

Additionally, because of their Stone Age technology, your tribe would disregard a lot of ideas that thanks to science we know today are actually real, simply because they lack the technology to observe and visualize them. To put it another way, your tribe would scoff at the idea of DNA/genetics, space travel, other planets, continental drift, and evolution, because it cannot be explained by the physical phenomena that they are able to observe in their environment.

The issue with your idea is that there is no way for the tribe to be able to parse between what we would consider obviously supernatural explanations and physical ones. The reason that humanism became popular is because of the advent of technology that allowed us to prove and disprove certain beliefs. God stopping the sun in Joshua makes no sense in a universe that runs on heliocentricity. Spontaneous generation makes no sense when you can isolate and sterilize something see that nothing grows on it. In a world where you only have Stone Age hunter-gatherer technology, how do you know that a volcano erupting or lightning striking isn't because some god or spirit did it? How can you prove otherwise? There's no way to test either Oog's hypothesis that Vulcan did it or Ugh's hypothesis that it was due to natural processes deep below the Earth's crust.

The thing is ancient people weren't stupid. Their beliefs in gods and spirits really were things that made logical sense to them. And in many cases the beliefs did have actual reasons behind them, they worked but not for the reasons that ancient people believed. For example the Chinese Mandate of Heaven may seem silly until you realize that widespread famine and disaster can easily be caused by governmental mismanagement instead of divine providence, and it could be taken as a sign the government is incompetent and must be deposed.

In many cases their beliefs became outdated and you had people desperately holding onto them through faith alone, but the original reason they were adopted was not because they were stupid. It was merely because they didn't have a complete understanding of the phenomenon. And to be honest more recent scientists aren't much better, what with historical researchers believing all sorts of dumb ideas that don't make it into the science textbooks (e.g., Newton and his mysticism).

Another question you have to ask is what purpose does this behavior serve? The scientific method became popular mostly among Western aristocrats who had enough resources and time that they could afford to sit down and run repetitive experiments to rule out all possible alternatives, or sit on their butt theorizing and writing equations. For a Stone Age society that is more concerned about day to day survival and is working a lot of the time, and who does not have a need for complex mathematics or have access to things like paper or parchment, what good does this behavior serve? In terms of day to day survival, the superstitious person will do just as well (if not better, due to higher caution) than the humanistic one.

Additionally, because of their Stone Age technology, your tribe would disregard a lot of ideas that thanks to science we know today are actually real, simply because they lack the technology to observe and visualize them. To put it another way, your tribe would scoff at the idea of DNA/genetics, space travel, other planets, continental drift, and evolution, because it cannot be explained by the physical phenomena that they are able to observe in their environment.