Some have alleged that if God used evolution to bring about life on Earth, that He must not be all-good because that would mean there has been a tremendous amount of animal suffering, and moreover, since God could have created life without using evolution, that He chose the crueler means to bring about life on Earth. A crucial premise in this argument is that animals are self-aware of pain as subjects, but the verdict is still out on this and there are plausible reasons to regard this premise as false. Thus, we would have an undercuttting defeater for this version of the problem of evil. The following link will take you to the SEP entry on Animal Consciousness to see what I mean:
http://plato.stanford.edu/entries/consciousness-animal/
http://plato.stanford.edu/entries/consciousness-animal/