YAM

Not, not Yam the Semitic deity of the sea, appointed divine kingship by his papa El until Yam was killed by his enemy Baal, but Yet Another Missing Link.*

Flatfish (for example, the quite delicious, but now threatened Dover Sole) are born - similar to other fish - bilaterally symmetric, with one eye on each side of the body. However, at an early stage of development, the left eye migrates to the right side of the head.

The highly asymmetrical nature of flatfish (Pleuronectiformes, or "side swimmers") skulls has been used as ammunition by both scientists - who claimed sudden evolutionary changes - and creationists who continue to argue against (at least macro-) evolution.

But now, a University of Chicago evolutionary biologist has found evidence of transitional fish forms that support the hypothesis that this asymmetrical eye position evolved over thousands to millions of years.

For more details, I refer you to The eyes have it at Nature and A Wandering Eye at Science News (don't forget to check out the two short videos there).

I would also be remiss if I didn't reference The Bat, the Bird, and the Flatfish by Jewish Atheist.

(*Note that "Missing link" usually refers to human transitional species. I just thought that poetic license should rule over using YATS or YAML.)