The Gosepl According to Darwin III

In this week's Gospel reading, the great prophet tells how the hands of our magnificent Creator have worked upon functionally duplicitous organs to give rise to new structures with new functions, in all their wonder and perfection. Indeed, this is revealed as the very mechanism that He used to carefully craft the swimbladders of our fish ancestors into the perfect yet peculiar structure of the human lungs, and provides us with an explanation for the mystery of the gill slits of the human embryo. Not only this, but Darwin in his infinite wisdom also foreshadows the discovery that our genes themselves are created by this very same process of duplication and refinement, made over a century later by the Disciples of molecular biology.

"If it could be demonstrated that any complex organ existed, which could not possibly have been formed by successive, slight modifications, my theory would absolutely break down. But I can find out no such case... We should be extremely cautious in concluding that an organ could not have been formed by transitional gradations of some kind...

Again, two distinct organs, or the same organ under two very different forms, may simultaneously perform in the same individual the same function, and this is an extremely important means of transition: to give one instance, -there are fish with gills or branchiae that breathe the air dissolved in the water, at the same time that they breathe free air in their swimbladders, this latter organ being divided by highly vascular partitions and having a ductus pneumaticus for the supply of air...In all such cases one of the two organs might readily be modified and perfected as to perform all the work, being aided during the progress of modification by the other organ; and then this other organ might be modified for some other and quite distinct purpose, or be wholly obliterated.

The illustration of the swimbladder in fishes is a good one, because it shows us clearly the highly important fact that an organ originally constructed for one purpose, namely, flotation, may be converted into one for a widely different purpose, namely, respiration. The swimbladder has, also, been worked in as an accessory to the auditory organs of certain fishes. All physiologists admit that the swimbladder is homologous, or "ideally similar" in position and structure with the lungs of the higher vertebrate animals: hence there is no reason to doubt that the swimbladder has actually been converted into lungs, or an organ used exclusively for respiration.

According to this view it may be inferred that all vertebrate animals with true lungs are descended by ordinary generation from an ancient and unknown prototype, which was furnished with a floating apparatus or swimbladder. We can thus, as I infer from Owen's interesting descriptions of these parts, understand the strange fact that every particle of food and drink which we swallow has to pass over the orifice of the trachea, with some risk of falling into the lungs, notwithstanding the beautiful contrivance by which the glottis is closed. In the higher Vertebrate the branchiae have wholly disappeared-but in the embryo the slits on the sides of the neck and the loop-like course of the arteries still mark their former position. But it is conceivable that the now utterly lost branchiae might have been gradually worked in by natural selection for some distinct purpose: for instance, Landois has shown that the wings of insects are developed from the tracheae; it is therefore highly probable that in this great class organs which once served for respiration have been actually converted into organs for flight."

A Reading from The Book of Darwin

- Charles Darwin,
The Origin of Species By Means of Natural Selection or The Preservation of Favored Races in the Struggle For Life, Chapter VI - Difficulties of the Theory. Modes of Transition

The Gospel According to Darwin II

On this, the holiest of days, the birthday of our prophet Charles Darwin, we celebrate with a reading from the divine scriptures. In today's Gospel reading it is revealed how the tool of natural selection was patiently wielded by the almighty Creator to sculpt the perfect structures of life.

"It is scarcely possible to avoid comparing the eye with a telescope. We know that this instrument has been perfected by the long-continued efforts of the highest human intellects; and we infer that the eye has been formed by a somewhat analogous process. But may not this inference be presumptuous? Have we any right to assume that the Creator works by intellectual powers like those of man? If we must compare the eye to an optical instrument, we ought in imagination to take a thick layer of transparent tissue, with spaces filled with fluid, and with a nerve sensitive to light beneath, and then suppose every part of this layer to be continually changing slowly in density, so as to separate into layers of different densities and thicknesses, placed at different distances from each other, and with the surfaces of each layer slowly changing in form. Further we must suppose that there is a power, represented by natural selection or the survival of the fittest, always intently watching each slight alteration in the transparent layers; and carefully preserving each which, under varied circumstances, in any way or in any degree, tends to produce a distincter image. We must suppose each new state of the instrument to be multiplied by the million; each to be preserved until a better one is produced, and then the old ones to be all destroyed. In living bodies, variation will cause the slight alterations, generation will multiply them almost infinitely, and natural selection will pick out with unerring skill each improvement. Let this process go on for millions of years; and may we not believe that a living optical instrument might thus be formed as superior to one of glass, as the works of the Creator are to those of man?"

- Charles Darwin,
The Origin of Species. Chapter VI - Difficulties of the Theory. Organs of extreme Perfection and Complication.

Happy Birthday Charles.