"Hmm, okay. Let me show you an example."
Glen pulls up a pictures of a mountain lion, lion, tiger, bobcat, and several breeds of domesticated house cat.
"These all have a common ancestor. These-" she gestures to the housecats, "were bred by humans. The rest came about on their own. On most worlds, species barriers are not set in stone. Any trait can change over time. Definitions of species are often fairly arbitrary, and based on someone's best judgement. "