The environment (which comprises other species) is constantly testing the “truth” of a species, and if they fail to survive, then they have failed the test. New genetic mutations means new species are gradually produced, which is what makes it possible for “evolution” to take place.
The same principle works in epistemology. In order for knowledge to evolve, we must continually generate new ideas, then consciously test them against the existing body (environment) of knowledge. Sometimes, new ideas can be so powerful that they can even radically change the existing body of knowledge. As far as we can tell, “Survival of the Fittest” is an undeniable mechanism through which everything (even abstract ideas) evolves.
People who deny evolution in nature, are also denying evolution in the sphere of knowledge.
This sort of “evolutionary” epistemology was famously addressed by Karl Popper, who successfully explained how the Scientific Method tends to improve our knowledge of the natural world. The epistemological framework is called Critical Rationalism.