Blame Dizpop.

Specifically blame Dizpop the mouse, a rodent magician who lived back when everything grew on trees and Man was still running around half-naked and furry. He was a clever mouse and as stated before, a magician of no small talent. He could turn apples to oranges, make the trees blue and the water yellow, make flowers bloom in winter and make nuts and berries double in size. Being a mouse, most of his talents were used to find food and protect the other mice from fierce sabretooth cats and wicked wolves.

After a while most of the predators had moved on to easier prey, leaving the valley that Dizpop lived in un-stalked and un-prowled. As you can imagine, it didn't take long for the other animals to figure out that this area was a safe place to live. They started arriving from all directions, eating the food and stepping in the water, taking the best sleeping spots and keeping the mice up with their noise each night.

The worst offenders were the Oliphants, relatives of elephants. They had the largest tusks, the longest trunks, the fastest-swishing tails and the furthest-seeing eyes. They were, in short, the biggest creatures in the valley. Day after day they would nearly inhale the food. Night after night they would sleep in the best spots, or worse, stay up wandering about dizzily, drunk on fermented fruit from the highest branches of the fruit trees. The Oliphants were such an annoyance that the mice decided to leave their safe valley and look for somewhere with fewer Large Animals in general. They called on Dizpop to tell him of their plan...

...and just as they reached his burrow, an Oliphant, extremely drunk, wandered past and stepped on the head mouse in charge of the relocation. Squish went the poor mouse, and squash went the three mice next to him, and that was enough. Dizpop squeaked and muttered and puffed himself up, lights flashing off his fur and his eyes glittering brightly enough to get the drunken Oliphant's attention.

"See here," said Dizpop in a magically magnified voice, "see here, you can't go around squishing and squashing! It's just Not Done!"

The Oliphant looked around, then down at the ground. He picked up one of his great big feet and eyed the sticky mass that came up with it, sniffed it once, and went to put his foot back down. Instead he over-balanced and fell with a resounding thump on the rest of the mice gathered there, leaving only Dizpop (now floating in mid-air) un-squished. With a squeaky roar and a puff of smoke Dizpop disappeared.

The next morning when the Oliphants got up to find breakfast, as they did every morning, they were met at the best fruit tree by a startling sight. There was Dizpop, perched on the highest branch. On all the other branches were the mice who hadn't been at the squishing last night, squeaking amongst themselves and eyeing the Oliphants with extreme dislike.

"Here now, what's this about?" asked one of the Oliphants. Another one chimed in, "Yes, why're you in our trees?" At that the mice begin to mutter instead of squeak and Dizpop, his voice magicked into a roar again, spoke.

"Your trees? YOUR trees? Oh, no. These trees, and this valley, and EVERYTHING in it isn't yours. You eat all the good food, you foul the water, and now you've squished our friends and our family. Enough is enough."

With that the mice began chanting, louder and louder, until they too were roaring. The Oliphants murmured, and spoke, and then they too were roaring as they charged the tree, intending to knock it over and squish all the arrogant mice in it. They ran faster, and the mice chanted louder...

...and as they ran, something happened! With each step they grew smaller and smaller and smaller... until they were as small as the mice. Silky fur and tiny eyes and a hint of a tail replaced four huge feet and the baggy fur-covered skin. Sharp teeth for gnawing replaced tusks for lifting. The trunk shrank, the eyes brightened. By the time the Oliphants reached the tree they were completely transformed.

"Now," said Dizpop, "you might suffer the same fate we have. You are small and furry, helpless and weak. However!" he looked out at the animals who had gathered at the edge of the fruit grove, watching silently. "However," he continued, "I will be kinder to you than you ever were to us. From this day forth, any of your cousins and brothers who dare to step on even ONE of you will find themselves brought down to your level. Literally."

The Elephants in the watching crowd looked quite nervous and one of them called out, "How are we supposed to tell which ones are them and which ones are you?" Dizpop merely grinned and replied, "Guess you'll have to avoid squishing any of us, just in case."

The tiny Oliphants scampered off, as did the mice... and the Elephants now avoid all small rodents, afraid that one of them might be one of the Oliphants, or as we now know them: Shrews.