When referring to the Amazonian forest, some people refer to it as a heaven for biodiversity, the green lung of the planet and also a wonder of nature That's not hard to understand why.
Words may be useful to describe all the breathtaking diversity that can be found in this area. Because of that, scientists were always curious how it all happened, and how this land became the capital of biodiversity.
To find the answer to this question, Dr. Scott Solomon, who is a professor at the University of Texas conducted a study. He collected genetic samples of several leafcutters and tested them in order to discover the mystery behind its diversity. One of the hypotheses that was proven to be valid was the Pleistocene refugia one.
This states that 21.0000 years ago there was a decrease in rainfall which had an impact on many species from the Amazonian forest. Because of that only a few of them were capable of surviving. What happened next is that the single species got separated in several multiple ones which all evolved differently based on the environment.
The result demonstrated that starting from one single species it ended with several ones totally different from the initial one. The second hypothesis which was found as a good answer to the main question was the "riverine barrier" one. It has a lot in common with the first theory as both of them are in favor of the precipitation of allopatric speciation. What this means is that the Amazon together with its tributaries rivers are enough in order to divide a single species into multiples ones because of the genetic drift and the selection pressure.
The study was able to bring us only a few reasons why all this happened. Definitely the flooding that took place thousands of years ago and the climate change had a huge impact on biodiversity but still, there might be other factors which remain unknown.