As nature is the source of all science, biodiversity is vital to scientific research, and there is no way to know what advancements may be lost with the extinction of a species. As long as we create, it is always derived from some type of nature, whether it be the nature of us, or a species or an ecosystem. The protection of species is important to human and scientific advancements, in general, including medicinal advancements.
Humans have learned about the world and even themselves through study done on animals. If an animal goes extinct that knowledge may be lost forever. For this reason it is vital to try to prevent the extinction of animals when possible. Different species offer different information to humans and any extinction is a loss to our ability to understand the world.