Chapter Eight - Lessons from the Embryo
THE fact that all the larger animals start from ova, or eggs, was first
published to the world in 1651 by William Harvey, the discoverer of the
circulation of the blood. But further knowledge of the stages in the development
of the embryo was long delayed, until K. E. von Baer (1792-1876), about
a hundred years ago, worked out the first comparisons between the developing
embryos of man and the various classes of animals. That they all start
alike and for many stages of their growth continue to behave in the very
same fashion, appeared so remarkable that during the second quarter of
the nineteenth century this fact gave rise to a great deal of speculation
as to the reasons for this similarity.
|Like Louis Agassiz (1807-1873) his contemporary, von Baer to the end of his long life rejected the theory of organic evolution. But long before he died the rather meager facts of embryology, as then known, had given rise to what is usually called the "recapitulation theory," which in the hands of Ernst Haeckel and others rapidly became by all odds the most popular argument in favor of the evolution theory. If within recent years this line of argument has much declined in favor among leading scientists, it has been because more recent discoveries in biology and embryology have tended to spoil the argument as contributing any support to the general doctrine made so familiar by Charles Darwin.||
A detailed description of the developing ovum is not essential for our present purpose. It may suffice to say that the one cell first goes through a complicated process of division and becomes two; each of these divides and thus there are four; then eight; then sixteen. Soon the developing embryo comes to look much like a mulberry, a round ball composed of a great many individual cells. Next the ball becomes like a hollow sphere, the cells composing merely the shell of this sphere. This is termed the blastula stage of the embryo; and it is a very interesting fact that all the higher forms of life develop thus far in the very same way, each passing through this blastula stage.
By the next processes of growth one side of this hollow sphere bends inward, forming a slight groove or depression, this depression becoming deeper until the two sides around it unite, thus forming a sort of double-walled sphere, which is now called the gastrula. With further development the gastrula lengthens out a little and becomes a short double-walled tube, with much more complicated processes a little later. We need not describe these next stages; but it must be noted that all of the higher animals, including reptiles, birds, mammals, and man, always pass through this same gastrula stage; and only afterwards do they gradually become more and more different from one another.
Why are all these animals alike in their early stages? Many people have
said that this resemblance is because the higher forms have all been evolved
from the lower kinds of animals, and that in its development the horse,
the dog, or the man must always pass through, of course very rapidly, the
stages through which its ancestors passed in the long ages of the past
when it was evolving to its present position. This is the famous "recapitulation
theory," which said that each of the higher animals repeats or recapitulates
some or most of the stages that its long line of developing ancestors went
through. And the evolutionists long pointed to these striking facts of
embryonic development as one of their strongest proofs of the theory of
A Better Explanation
But is there not a better and a more rational explanation than this whimsical one of recapitulation? All the higher animals start alike from a single fertilized cell, the ovum. How could any of them reach the higher stages of structure without all passing through many of their earlier stages side by side, or running parallel to one another?
For comparison, take the many lines of railway running Westward from Chicago. For considerable distances these roads run parallel to one another; but gradually some of them turn toward the south, some of them toward the north, while others keep on westward. Of these last, those going clear through to the Pacific Coast will keep together, or parallel to each other, for much longer distances than will those going to Texas or to Similarly, we might expect that the embryos of the higher animals, such as the dog, or the horse, or the elephant, will resemble the human embryo for a much longer period than will the embryos of the starfish, the frog, or the chick. The insect and the vertebrate would naturally begin to diverge from each other somewhat early in their development; though two insects, such as a house fly and a grasshopper, or two mammals, such as a dog and a horse, will maintain their resemblance to each other for a much longer period.
These facts follow from necessary first principles; they are of the very nature of things, and could not well be otherwise. As all the higher forms start alike from a single cell, a hundredth of an inch or so in diameter, all these cells or ova of the cat, the dog, the horse, the ape, or of man being at first so nearly identical that no powers of the microscope seem to show much difference between them, save in the number of the chromosomes they contain in the nucleus, or slight differences in the size of the ova themselves, -- since they all thus start alike, how could they develop into the higher forms without running more or less parallel to each other for some time, gradually diverging more and more from the common or average type?
This is all there really is to this wonderful "recapitulation" process, which in the latter decades of the nineteenth century was so very much overworked by Haeckel and his disciples as an argument for organic evolution.
The Fallacy in "Recapitulation"
Of course, these evolutionists had much more to their argument than the facts we have just given. They had three sets or series to compare. These three series were as follows:
1. The individual development of a single animal from the ovum to maturity.
2. The classification series, composed of all the typical animals arranged in a series, from the one-celled type up to one of the higher animals, or man.
3. The geological series, which also starts with rather small, lowly organized forms, and runs up to the higher or more highly organized types, man last of all.
The first of these series is an actual fact; it represents a real historical development. The second of these series is purely artificial; but it is a very natural one, and is a convenient one for purposes of scientific study. But up until quite recent years the geologists stoutly maintained that the third also represents just as true a natural order, just as much a real historical fact, as the lirst one, only a much longer one. Within the past few years, however, it has been proved that the third is just as truly an artificial series as is the second. Indeed, it is much like the second; for it simply represents the floras and faunas of the ancient world, found as fossils in the rocks from all over the globe. And the work of geologists in putting these fossils together into a series is just as much an artificial act as is the similar work of thc zoologist or the botanist in arranging the corresponding living forms into a series from the little to the big, from the simple to the complex in structure.
We are now able to get our bearings with reference to this argument
from "recapitulation." We see that the evolutionists are really comparing
one natural or real series of facts (No. 1), with two wholly artificial
series (Nos. 2 and 3), which as serial orders have each only a purely artificial
or constructive existence. The individual units of the classification series
and of the geological series really exist, of course; but the arrangement
of them in a serial order or line, one after another, is an arbitrary act
of the one making the arrangement. And hence, while these comparisons are
interesting and convenient for purposes of comparative study, the results
of such comparative arrangements of the facts of the modern animals and
of the ancient animals, with the one real historical order: namely,
that of the embryonic development of the individual, cannot prove
anything in favor of the theory of organic evolution. In fact, this "recapitulation
theory" never did prove anything at all except the ease with which people
can fool themselves and others by mere tricks of logic.
||Now I know that some friends of the evolution theory will protest that this matter of the "recapitulation" argument is not by any means as simple -- and as silly -- as I have here represented it. They will begin to talk about the "gill slits" in the human embryo, the "tail" it is alleged to show, and a number of other alleged "vestigial" parts or structures, some of which "persist" throughout life.|
The space here at my command will not permit me to do more than briefly to refer to a few general principles in this connection, referring the interested reader to my recently issued "The Phantom of Organic Evolution" (1924) for a more complete treatment of these topics.
What about the "Gill Slits"?
The so-called bronchial arches, or "gill slits," which are depressions or grooves below the head of the embryo, never actually open into the larynx, as do the real gill slits of fishes; nor do they ever have anything to do with the breathing organs, as do the true gill slits of the sharks and other fishes. The upper one of these arches finally develops into the upper jaw, the second into the lower jaw, and the others develop into the various organs around the neck. They are necessary as preparatory stages for the structures to follow from them. Their fancied resemblance to the gill arches or gill slits of fishes has been much overstated by evolutionists; and this idea that they are the useless relics of a fish-stage through which man once passed in his upward evolution has been much promoted by inaccurate or even fraudulent diagrams (mostly "made in Germany") which have been copied from one book to another, often without the writers of the books knowing the real facts in the case.
Similar remarks could be made regarding the so-called "tail" of the
human embryo. Its use by some half-informed advocates of the evolution
theory as an argument, is not an evidence of much thinking or much embryological
information on their part. Several of the ductless glands of the human
body, such as the thyroid, the pineal, and the pituitary, were once pointed
to by the evolutionists as useless relics or vestiges of man's inheritance
from his animal ancestors. Modern discoveries in physiology have put a
stop to this argument. But until these discoveries of the real uses of
these organs, this argument of the evolutionists was among the most effective
they had along this line.
Big Strawberries on Top
If we return to a consideration of the present status of the "recapitulation theory," we shall find that it has but few defenders among biologists of the first rank. Adam Sedgwick admits that there is a general resemblance between the embryo and the larval stage of certain animals; but he adds that "this resemblance, which is by no means exact, is largely superficial and does not extend to anatomical details."
Dr. Percy Davidson, of Leland Stanford Junior University, has written a treatise entitled: "The Recapitulation Theory and Human Infancy" (1914). It is a mine of information regarding this whole subject. But in his summary of the present situation Davidson says:
"From these authoritative statements it appears that the facts of embryonic resemblance fail to support recapitulation in all three of its main implications.
"The order of appearance of characters is not uniformly, or even commonly, that required by recapitulation, which is first those representative of the order, and then in succession, of the family, genus, and species. . . .
"In the second place, embryonic resemblance in comparable stages does not vary directly with remoteness of kinship, but shows often very great divergence from this rule. . . .
"Finally, where resemblance does exist, it is not identity, nor even close [resemblance]." -- Pages 34, 35.
L. C. Miall, in an address before the British Association in 1897, said:
"The best facts of the recapitulationist are striking and valuable, but they are much rarer than the thoroughgoing recapitulationist admits; he has picked out all the big strawberries and put them at the top of the basket." -- "Proceedings" (1897), p. 682.
William His, one of the most eminent of embryologists, says:
"In the entire series of forms which a developing organism runs through, each form is the necessary antecedent step of the following. If the embryo is to reach the complicated end-forms, it must pass, step by step, through the simpler ones. Each step of the series is the physiological consequence of the preceding stage and the necessary condition of the following." -- Quoted by T.H. Morgan, "Evolution and Adaptation," p. 71.
A Mere Bypath
And Professor His declares that Haeckel's method of comparison is a
"mere bypath," and is "not necessary at all for the explanation of the
facts of embryology."
|Oskar Hertwig, another eminent authority, says:
"We must drop the expression 'repetition of the form of extinct forefathers,' and put in its place the repetition of forms which are necessary for organic development and lead from the simple to the complex." -- Quoted by T. H. Morgan, op. cit., p. 79.
"The recapitulation theory is mostly wrong; and what is right in it is mostly so covered up by the wrong part that few biologists longer have any confidence in discovering the right."
"The critical comments of such embryologists as O. Hertwig, Keibel, and Vialleton, indeed, have practically torn to shreds the aforesaid fundamental biogenetic law [of Ernst Haeckel]. Its almost unanimous abandonment has left considerably at a loss those investigators who sought in the structure of organisms the key to their remote origin or to their relationships." -- Scientific American, February, 1921, p. 121.
So much then for the notorious "recapitulation theory," which the uncritical
zeal of Haeckel labeled the "fundamental biogenetic law." This theory
originated when the facts of embryology were new and but imperfectly understood;
it was brought into prominence by means of an aftificial arrangement of
the fossils which seemed to resemble the embryonic development from the
simple to the complex. It has now collapsed with a more accurate
and more complete knowledge of the developing embryo, and especially with
the exposure of the artificiality of the geological arrangement of the
||In short, as I have said elsewhere:
"The recapitulation theory, as an argument for organic evolution, was
founded on ignorance and deceptive comparisons; it has now outlived its
popularity among those evolutionists who feel obliged to depend henceforth
upon honest arguments to promote their theory. To continue to use
the recapitulation theory as it was used by Haeckel and Darwin, can no
longer be regarded as an indication of intellectual honesty." "The
Phantom of Organic Evolution" (1924), Chap. VII, past para.
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