User blog comment:Maki Kuronami/Extra Lesson: Attack on Grimm/@comment-4010415-20141017003357/@comment-24891101-20141017004414

Couple holes there: Grimm are functionally immortal, so a matter of a few years will not make much difference. And if the captive died from lack of negative emotions, then Grimm in the wild could not live long, far away from people.