Hereditary Changes Cannot Occur Without Reproduction
What does one do when one cannot seem to evolve quickly enough or at all? You guessed it, the species dies. Even more important than this is that sometimes a species will die off simply because it cannot reproduce. Loner animals, such as most species of Rhino, have seen this issue. For many years, poachers killed several rhino species in Africa. The Northern White Rhino, a very beautiful species of Rhinosaurus, was hunted by poachers for decades due to its horn.
Rhinos use the horn as a tool and weapon, which means its removal can be harmful in several ways. For example, even if it survives being shot by a poacher, it could still die from other predators that choose to attack. If it needs the horn for a tool purpose, especially when using it to obtain food, it could die from the lack of food resources. In any case, we know this same species of Rhino does not reproduce in large numbers.