I’m just applying the “scientific method” to this situation. Thousands of years ago people relied on their observational skills and integrated relationship with nature to survive and thrive. The most elementary application of this was to determine what was edible and nutritive. Much of this knowledge was known even before modern day Homo sapiens. Eventually this skill allowed certain individuals to deduce potential medicinal value of certain plants. Undoubtedly experimentation was involved, most certainly on others. There were lots of failures, after all. And again, some of this knowledge was gained by trial and error before the advent of Homo sapiens.

But what of ancient peoples who ventured into new territories, often with completely different flora and fauna? They had to apply the scientific method without much stored wisdom. Exceptions would be similar plants that might be found in Amazonia as in Africa, but the people in Amazonia didn’t get there straight from Africa. So, they needed a process to determine what was edible, nutritive, and medicinal all along their journey. Pretty fascinating.

That’s my guess.