The researchers settled on a spectrum of ways that organisms can tolerate humans. A “domestic” population is adapted to a human-associated niche.

Now, scientists from the University of Calgary have analyzed the emissions of these photons in mice before and after death, showing how they quickly dim as a result of an organism’s passing.

And bedbugs require a human host—or a bat living near a human. ( Ancient DNA shows cats domesticated themselves .) The researchers settled on a spectrum of ways that organisms can tolerate humans.