Symmetrical versus asymmetrical globe placement: It's no fluke

Key Points

As you are no doubt aware, the competing theory of "intelligent design" has been proposed as an alternate explanation. My own view as a scientist is that the resulting controversy and debate has been healthy and has resulted in new opportunities to prove or disprove parts of Darwin's theory.

Two of these curiosities, interestingly, relate to the eye. One concern is how a highly complex organ such as the eye might develop if there are not intermediate forms of rudimentary eyes that confer a survival advantage to the organism.

But they don't start out life this way. When born, they have one eye on each side of the head. Then, as they mature, one eye amazingly migrates to join its fellow, and they become the funny-looking adults we know and love (to eat, within hours of being caught, cooked on the grill wrapped in heavy-duty aluminum foil with butter, fresh ground pepper, and lemon slices until white and flaky, accompanied by a not-too-oaky chardonnay).

Moving an eye around, as you might imagine, is no small matter. It involves remodeling of hard and soft tissues, and at least one gene has been identified that seems to be involved in making this happen.¹

But how could-and why would-evolution result in such a situation if there were no intermediate forms (animals with partial migration of the eye) or survival advantage from such partial migration?

I must admit that this struck me as quite the conundrum until I saw in a recent issue of Scientific American that an intermediate life form recently has been discovered.² The 50 million-year old fossils of this flatfish possess asymmetrical skulls. The hypothesized advantage is that having the oddly shaped skulls helped this carnivore catch its meals.

Considering that there are humans with disorders characterized by eyes being too close together or too far apart, having a full understanding of how this all works would seem to have implications for helping patients.

My favorite aspect of the flounder story involves my friend Karen, who is a gynecologist in practice in southern California. I have a witness to this event and Karen's permission to share it. Karen is very pretty (a feature typical of the spouses and significant others of ophthalmologists). The anecdote: while in medical school at the University of California, Davis, Karen was listening to one of her professors lecture on the topic of embryology. The professor told the story of how the young flounder one day experiences its eye moving across its head. Not growing up near the ocean or having fished, she was hearing about this phenomenon for the first time, and the description and photos naturally made quite an impression on Karen. "Oh no," she exclaimed in the middle of the lecture room. "I hope that never happens to me!"

Peter J. McDonnell, MD director of the Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, and chief medical editor of Ophthalmology Times. He can be reached at 727 Maumenee Building, 600 N. Wolfe St., Baltimore, MD 21287-9278 Phone: 443/287-1511 Fax: 443/287-1514 E-mail: pmcdonn1@jhmi.edu

References

1. Bao B, Yang G, Liu Z, Li S, Wang Z, Ren D. Isolation of SFRS3 gene and its differential expression during metamorphosis involving eye migration of Japanese flounder Paralichthys olivaceus. Biochim Biophys Acta. 2005;1725:64-70.

2. Choi CQ. Evolution. Not so rapid eye movement. Sci Am. 2008;299:34.