of mice and design

Dembski points to this article to ask, "How much intelligence is required to build self-repairing systems?" (An interesting, albeit loaded, question.) The exciting discovery:

Scientists have created "miracle mice" that can regenerate amputated limbs or damaged vital organs, making them able to recover from injuries that would kill or permanently disable normal animals.

The experimental animals are unique among mammals in their ability to regrow their heart, toes, joints and tail.

Since Dembski hasn't, I'll consider the metaphysical implications. Let's assume that self-repair is, in fact, designed. Some immediate questions, then. Why can fish and amphibians regrow organs and limbs, while mammals--never mind humans--can't? Is it an inscrutable whim, a design constraint, a purposeful omission?

To press the theodicy question, what might be the motives of an omnibenevolent designer to deny such radical self-healing capabilities to otherwise favored beings?

Some potential answers. First, if the designer's motives are entirely inscrutable, inquiry stops there. Second, self-repair isn't an obvious design constraint; witness the healthy functioning of the amped-up mice. Third, I can imagine a creationist response to the third possibility--self-repair is a postlapsarian loss--but if so, again, why fish and amphibians weren't affected is a mystery.

As to the theodicy question (which I grant is packed with certain assumptions), I leave that to the theodicists.