The superior oblique muscle

Part of an irreducibly complex system

The superior oblique muscle is one of the six external muscles on each eye. It has a fascinating and unique anatomy. Arising from an attachment in the bony orbit, its tendon goes forward and through a loop attached to the orbit called the trochlea and then, slung on the trochlea, it doubles back to be inserted on the top of the eye. When it contracts it moves the eye downwards and tends to rotate it inwards. In its function it is always in opposition to the inferior oblique muscle, which lies under the eye and which moves the eye in an equal and opposite direction. Neither muscle can act without being in tension with the other. The superior oblique muscle, like all the other eye muscles must act in harmony and in tandem with the other 5 external muscles of each eye.

 

The control of eye movements is not fully understood and is immensely complex. Even when fixing your gaze on an object the eyes must have a slight shivering movement so that the image on the retina is not stationary. If stationary then the image will rapidly fade.

 

While reading this article try bending your head towards one shoulder. Your eyes will compensate for this movement so that your gaze remains steady on what you are looking at. This is primarily done by a reflex nervous connection between the vestibular canals in your inner ear (which detect the movement of your head) and the eye muscles. All the eye muscles must work together to achieve this. You are unconscious of what is happening but it is a wonderful and poorly understood mechanism.

The image you see is a composite of the input from both eyes. Any defect of the external eye muscles will cause double vision. To achieve a single image, particularly for close objects, requires binocular coordination of the eyes; the eyes are positioned at slightly different angles to achieve a single image.

Why is this important for discussing intelligent design? It is important because there is no evolutionary mechanism to produce a muscle like the superior oblique. It is irreducibly complex. There are no intermediate steps in evolutionary terms, as I will explain in this article. Much of what I write could be applied just as well to the other parts of the eye.

Firstly, look at its anatomy. To work as an effective muscle it must loop through the trochlea and back on itself to attach to the eye ball. It must have a minimum of a bony attachment in the orbit, a trochlea to pass through and an insertion into the top of the eyeball, an intimate connection to the nervous system and a blood supply. Its attachments must be precisely positioned to have any use. Without the trochlea it would not work. All must be in place perfectly for it to function.

Then see how it must work in harmony with the other muscles of the eye. It has to have dynamic tension with the inferior oblique muscle. It must be connected via the nervous system to a variety of centres that allow it to function together with the other muscles. There is the vestibular apparatus that we have mentioned, the unconscious micro movements that allow you to gaze at one object, the binocular coordination of look at close objects and of course the action of voluntary moving of your gaze.[1]

For the Darwinist there must be a possible series of intermediate steps all leading to something as complex as the superior oblique muscle. No evolutionary thinker would think it could arise de novo, as it is now. The first step must be simple and only require some mutation to create a novel structure. Then each subsequent step must have an improvement or survival value for it to be selected and passed on to future generations. The problem is that the superior oblique is not just complex but must have a minimum degree of specific attributes to function at all. I have listed these minimum attributes above. How could some series of random mutations bring these about? The muscle cannot function without its precise attachments, the trochlea through which its tendon passes, its dynamic tension with the inferior oblique muscle, and its immensely complex connection to the brain which controls its movements in harmony with all 5 other muscles of that eye (as well as all 6 muscles of the other eye). Remove any of these and there is complete and total breakdown of vision.

Eyes of various types have arisen many times in the animal kingdom. The ‘camera’ type eye, which we possess, has arisen separately many times. There is no smooth trajectory from simple to complex seen in the fossil record[2] or as propounded by Richard Dawkins in his book The Blind Watchmaker[3]. In that book there is a remarkably naïve and entirely ‘made up’ story of gradual changes leading to the human eye.

The very first eyes, which we find in the lower Cambrian strata, about 530 million years ago are superb compound eyes seen on the trilobite.[4] They appear abruptly. They are magnificently engineered. And when vertebrate eyes appear in the fossils they do so abruptly also.

Should we not call for more transparency and hard evidence in the scientific discussions about eye evolution?

A much quoted sentence in Darwin’s great work ‘On the origin of species’ is the following:

To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree.[5]

Now the quote should be taken in context and that context includes Darwin’s eventual belief in his own theory. I would strongly recommend reading the whole book. But his quote nevertheless does have more resonance than the Darwinist will admit; and even more so now that we understand what mutations can and cannot achieve and the rich fossil record we have today.

 

References

[1] Oyster, Clyde. 1999. The Human Eye. Structure and Function. Sinauer.

[2] Land & Nilsson. 2002. Animal Eyes;. Oxford

[3] Dawkins Richard. 1986. The Blind Watchmaker. Longman

[4] Clarkson E.N.K. 1998. Invertebrate Palaeontology and Evolution. Blackwell

[5] Darwin, Charles. 1859. On the Origin of Species. John Murray

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