Just as new species are constantly evolving, old ones are going extinct. Such background level extinctions are the consequence of natural selection, when species can no longer cope due to changes in their ecosystems to which they can’t adequately adapt. One of those changes is the evolution of new species. The march of evolution is not, however, some sort of progress, in which species are becoming better and better. This is teleological thinking, like the Great Chain of Being (), and has no scientific value.
There’s also no evidence for built-in senescence or obsolescence of species, which makes sense: there’s no way to select for such a trait, just as there’s no way to select for a trait ahead of time that would be a useful response to a future, novel challenge. We can also rule out the idea that species can acquire traits through the life experience of individuals. There’s no mechanism whereby your offspring can be made stronger through inheritance of a strength you’ve acquired by pumping iron, because there’s no way to program your genes to specify the acquired property.