What if it happened "naturally", as a result of workers infecting thousands of mice and killing the ones that stayed healthy, then reinfecting new mice from the

What if it happened "naturally", as a result of workers infecting thousands of mice and killing the ones that stayed healthy, then reinfecting new mice from the remainder, over and over for many generations? Or you did the same except used tissue samples instead of live mice? Yes, you merely allowed evolution to "uncover" it, but if you paid for this work you certainly helped it along.