Humans have been driving other species to extinction for a very long time. Just since the last Ice Age some 255 species of mammals and 523 species of birds have gone extinct, and most of them due to human activity.
We move species to new regions and domesticate others. All of this can lead to the destruction of a number of unique life forms, so much so that current extinction rates may result in a sixth massive extinction, this one entirely our fault.
All that human activity doesn’t just destroy, though, and in fact a number of species have actually developed because of human activity. More new species of plants exist in Europe than have gone extinct over the last three centuries. The London Underground mosquito can no longer breed with above ground mosquitos, making it a new species (that was certainly an accident, since nobody actually likes mosquitos).
Humans create novel environments in which new species can develop, or we change existing ecosystems enough that species develop significant variation and can branch off into new species.
But these new species can’t replace those we’ve lost. London Underground mosquitos didn’t evolve to fill a niche left by an extinct blood-sucking insect–they just evolved. We can’t replace lost species, because they each had specific contributions to their native ecosystems. Every species is unique, and even when they fill niches similar to other species, they aren’t quite the same niches. Even if we were creating new species as fast as we were driving others to become extinct, it wouldn’t offset the damage; those new species would be square pegs for round holes. Or mosquito shaped pegs for black rhino shaped holes.
Conservation is still important, and essential to preserving existing ecosystems. But knowing that we also drive the development of new species is something we need to keep in mind as we work to preserve already endangered creatures.