* * * * *
Whenever new perspectives appear in the history of human knowledge and shed new light on established facts, reorganize scientific groups, and attempt to lead them to new directions, one is obliged to comment on such reforming ideas, especially if one is teaching a relevant science.
This is one of the motives which leads me to present before you today my views on a theory that was introduced only ten years ago, but today already exerts a powerful influence on all the sciences of organic life: the Darwinian theory Footnote 2*of the origin of species.
There is a second motive. In the decade since the publication of Darwin's book, all the arguments raised in it have been the subject of lively discussion. At present, with our current knowledge, we can claim that the arguments to support or refute the theory, which are based on the data we have gathered so far, have been rather general. Therefore, it seems prudent to bring into the spotlight all the available data in order to review within their framework the scope of the whole question. There are many commentators on the Darwinian theory, and they frequently suffer from a certain measure of vagueness (although the critics suffer from this more often). I shall briefly review those commentaries first.
This vagueness stems from erroneously confusing the transmutation hypothesis with the Darwinian theory: transmutation is a necessary and inseparable prerequisite of Darwinian theory, whereas the Darwinian theory is not a necessary corollary of transmutation theory. The view that the organic world is derived from a few simple forms from primeval times is not in itself a theory. It is a hypothesis upon which a theory can be built if one tries to determine the causes behind the transmutation from one form into another. Lamarck was the first to establish a descent, or transmutation hypothesis. Since Lamarck, like Geoffroy and Oken, considered the external conditions of life to be the primary agent of change, he sought for the causes of descent [with modification] in places other than those where Darwin sought. All these theories are based on the transmutation hypothesis, but their account of this hypothesis is a different one.
Therefore, considering the Darwinian theory, there must be a sharp distinction between its underlying (transmutation) hypothesis and the arguments building upon it. Objections directed against the latter must not in the least weaken the first, which is to be measured by a completely different standard.
Such a distinction appears to be crucial if one envisions the essence and significance of a scientific hypothesis. The term scientific hypothesis carries with it the impossibility of proof: it appears justifiable wherever direct observations are no longer sufficient to understand a number of phenomena from a conjoint viewpoint. The more inclusive a hypothesis is, the more confidence we have in it, i.e., are able to derive from it new questions. This is like the case of the Copernican world-system, which today we consider to be well founded. The Copernican world-system too is only a hypothesis, one which the great discoverer himself claimed was driven by the conviction that the geocentric hypothesis – then the prevailing assumption – was not sufficient to describe the motion of celestial bodies. Copernicus said, “I started to wonder whether one could find better explanations by assuming a moving earth. I found that when the movement of the other planets was compared to that of the earth, it was possible to explain better not only the earth's motion, but also the other planets’ trajectories. I realized that the entire planetary system is interwoven – as far as the criteria of size and order are concerned – and that it is impossible to change any part of this system without disturbing the whole and creating disarray.” It was in this way that the heliocentric hypothesis was completely justified in those days, since it explained the major bulk of astronomical phenomena, while avoiding conflict with any of them, i.e., it provided what a scientific hypothesis should provide.
Just as at the time of Copernicus the heliocentric hypothesis was in opposition to the geocentric one, nowadays the transmutation hypothesis stands vis-à-vis the hypothesis of independent and simultaneous creation of species (which we call in short the old creation hypothesis). Let us now compare both hypotheses with respect to their scientific grounding, examine their bases as well as their merits, and see if any of them blatantly violates the facts.
The characterization of both hypotheses will be given shortly. The old creation hypothesis assumes that long ago all species were created simultaneously and independently from each other, and since then have reproduced in an unchanged form. In contrast, the transmutation hypothesis assumes as a given only a few very simple species, and derives from this beginning of organic life on earth the whole rich and vast living world of past and present periods. The transmutation hypothesis states that through gradual conversion of form, out of the first species new species emerged, those in turn again produced new species, and so on. It is clear that the foundations of both views are as different as they are themselves: the first relies on the immutability of the ancient species, while the other strictly demands variability of species; the first considers species as absolute, while the other considers species to be only relative, and perceives them only as loosely defined groups of similar individuals.
Today the debates over the foundations of both these hypotheses can be considered as completed; therefore I allow myself to present them briefly in what follows. Cuvier, as is generally known, tried to prove the immutability of species using research on the Egyptian ibis mummies, which show complete correspondence with the design of the modern ibis living on the banks of the Nile. This observation proves only that this particular species has not changed significantly for several thousands of years. Possibly it was a more stable form, or it did not have a reason to vary. It is unnecessary to emphasize how infinitely short such time periods are as compared to the incomprehensible long periods of earth's history. As long as the variability of the majority of species is clearly shown, the immutability of species will not be proven by using the fact that certain species occasionally remain unchanged for long periods of time. No one denies that species vary, but what does that mean other than that they are not immutable?
The question of the nature of the species had also not been answered by the old creation hypothesis. The absolute nature of the species, which is necessarily required by the creation hypothesis, cannot in reality be verified in any way. It has been shown that even a definition of species cannot be given, neither a morphological one nor a physiological one: the species is not sharply delineated, rather it often merges through countless intermediate forms, and therefore the species is an artificial and limited concept.
Given the above and according to the present state of knowledge, the new hypothesis has a more solid foundation than the old one. In the case of the points of concern presented above, much is a matter of individual opinion, especially the variability or immutability of the species. Since actual proof cannot be produced, let us abandon what we already know and treat both hypotheses as equally well founded, and move on to consider their merits.
The transmutation hypothesis assumes that the wonderful similarities among species – which until now have been described metaphorically as kinship and led to the establishment of a so called natural system: genera, families, orders, classes and spheres (phyla) – consist of a real blood relationship, and that related animal species stem from a common ancestor. It is the solution to a riddle that was poetically phrased by Goethe “All the shapes are similar, though none equals the other, and so the choir points to a secret law.”
We see that in a fish the axis of the body is a strong column (the spinal column), on which the central parts of the nervous system are located and under which the vegetative organs of nutrition and reproduction lie, both enclosed by arch-shaped appendages from this column. We find the same arrangement in amphibians, reptiles, birds and mammals, but we also observe a totally different arrangement of parts in a mass of other animals. Therefore we inquire, with justification, as to the causes of this striking correspondence. The transmutation hypothesis gives us the answer, positing that all vertebrates arose from a single ancient vertebrate species.
We hope in vain to understand these facts with the help of the old doctrine. Although the old doctrine speaks of the creator's plan, what is it other than the recognition of an internal unity in the organismal world, combined with a simultaneous abandonment of the attempt to understand it? It is awkwardly translating the facts, yet if this plan has been implemented it was only in a very disparate and incomplete way, since several equivalent groups, for example the vertebrates, are sometimes represented by many families and orders, and at other times only by few genera or even only by a single species, as in the case of Amphioxus. How are we to consider intermediates between such main groups? The old doctrine provides no answers, whereas the transmutation hypothesis derives support from such intermediate forms.
The same situation occurs with the data used in comparative anatomy's description of animal design. Let us consider for the time being only the case of vertebrate limb formation: considering all the differences, we can still find a wonderful correspondence: correspondence of all bony parts, be they completely developed (like the arms and legs of the highest mammals), be they partially atrophied or fused or totally missing, be they stretched and accompanied with hooves for running, be they short with toes, with claws designed for climbing, digging or securing prey, be they transformed to fins (as in fishes and cetacean), or be they a flight organ, as in birds, bats and flying fish! No comparative anatomist can deny that the design of these animals indicates they all are related to each other, as if they originated from a common ancestor.
In the case of embryology [Entwickelungsgeschichte], we are again faced with an infinite number of facts, which can be explained only by the transmutation hypothesis. Consider the striking similarities between the first embryonic rudiments of all vertebrates, regardless of the different designs exhibited by animals in this sphere. Post-embryonic development is similarly rife with such facts. During the development of barnacles and parasitic crustaceans, it is difficult to determine to which class they belong, and their crustacean nature can be recognized only by inspecting their young form. Since the revival of the transmutation theory, much attention has turned to research on developmental history, as is best illustrated by the admirable work of F. MüllerFootnote 3* on crustaceans. This distinguished researcher outlined the basic features of the developmental history of this class. He showed that the lowest orders of Crustacea leave the egg as nauplius larvae, and then reach the body form of Cirripedia and Entomostraca through different metamorphoses. He has also shown that in the highest order of Crustacea, such transformations do not occur and the young animal leaves the egg in the complete developed shape or as a zoea, which is a much more developed larval form than the nauplius. Müller demonstrated that in some species first a nauplius larva is found, and only then do further metamorphoses lead to the zoea form, and the final developmental stages progress similar to other Malacostraca.
Regarding these facts, the old doctrine has nothing to say: it can only accommodate them at face value. If one asks why does PeneusFootnote 4* leave the egg in the form of a nauplius (like the smallest Entomostraca, Cirripedia and parasitic barnacles), while most of its closest relatives leave the egg in the higher larval stage of a zoea, the old doctrine can at most give only a teleological answer, which in itself would be problem enough. Only the transmutation theory, which sees in the developmental history [Entwicklungsgeschichte] the rather complete picture of the species’ development, will provide real understanding.
Only from this standpoint it is possible to realize that the larvae of related species (e.g., insect larvae) resemble each other during earlier developmental stages, just as adult forms resemble each other in the fully developed stage. Larval resemblance includes not only the fundamental characteristics of form, but also secondary features. Why, for example, do all Chaerocampa (genus SphingidaeFootnote 5*) caterpillars, such as Ch. nerii, celerio, elpenor and porcellus, possess eyelike spots on all their thoracic segments? The spots are not transferred to the butterfly stage, and are totally unrelated to it, just as in the case of the forklike horns of the Papilio (P. machaon and podalirius) larva that protrude from its neck.
Only the transmutation theory can explain paleontological data. It has been established through thousands of observations that the extinct species of earlier epochs showed a certain regularity in their distribution. We see classes of animals that are at first always represented by only a few species, then follows a gradual increase in numbers, culminating in extraordinary richness, and then a decrease in later periods to a smaller number of species and finally extinction. For example, during the first geological epochs, only a few species of ammonite were to be found, whereas the Jurassic and Cretaceous periods see a sharp increase in numbers, and they completely die out in AnteocaenFootnote 6* times and are missing in the Tertiary and Quaternary periods.
It never happens that classes of animals that appear in one layer are completely absent from subsequent layers, and re-appear in much later ones. However, such a finding would not have been a surprise for the old creation hypothesis. To explain the appearance of new animal forms in later geological layers, the old doctrine can only resort to the act of creation. The only explanation this theory provides is the resurrection of long extinct species.
If it could be proven that an animal class lived during the Silurian period, later became extinct and, much later, approximately in Tertiary times,Footnote 7* surfaced again, the transmutation theory would suffer a blow. We find just the opposite, i.e., extinct genera never re-appear, and everywhere there is a continuous connection of related species. We can even quantitatively demonstrate how genera, families, orders, etc. originate, flourish and then become extinct again, and that is exactly the same as in an individual life history. This goes to show that only the transmutation theory can make sense of paleontological findings.
The geographic distribution of organisms also provides data that the creation hypothesis cannot explain. Judging from the peculiar manner in which species are distributed on earth, it is evident that external conditions (such as climate, soil and nutritional conditions) are only of secondary influence on the existence of species. Even though, supporting Darwin's argument, you can find regions in South America with climates rather similar to those in South Asia, they are inhabited by different species. It follows that the species had originated in one location and from there were dispersed in all directions that presented no obstacles to their migration (e.g., as oceans prevent the migration of terrestrial animals, and as land barriers do similarly for marine animals). This explains why rivers often constitute the geographical distribution-limit of wingless species of bugs. The species of sea snails, crustaceans and mussels living on the Atlantic coast of Central America are totally different from those that occupy the west coast, which are sometimes separated by only a few miles, but are not connected by a tongue of water.
These facts can still be accounted for by the old creation theory.Footnote 8*
However, only the transmutation hypothesis is capable of explaining data relating to the striking similarities between species that live in the same space and also between temporally successive species.
Only by assuming a continuous transformation of species can we understand why the species of a bigger group, for example the monkey order, on one continent (e.g. America) are all more closely related to each other than to any other monkey species from Asia or Africa. Only then can we understand why animal species on an island are most closely related to those of the nearest continent, even though they are not identical to them. Only from this standpoint is it possible to conceive why the most developed animal forms – the mammals – are absent from islands in the Pacific. An exception to this is the bats, but in their case as well, islands are not characterized by the same species as are found on continents, and almost every island possesses one or more endemic bats species.
How would the old creation hypothesis treat the fact that no other mammals were created on these islands, even mammals that now thrive so splendidly that they turn wild again after they have been introduced to these islands by the Europeans? All it offers as an answer is that such a question is beyond the scope of human understanding, an answer that amounts to nothing more than self conviction.
Here, again, the old doctrine is baffled when confronted with such problems and cannot even fathom a solution.
From the above it follows that the transmutation hypothesis is infinitely superior to the old doctrine in its productivity. Yet, one point still demands attention before we can evaluate both hypotheses. A scientific hypothesis can never be proven, only refuted.Footnote 9* Therefore we look for facts that are at odds with any one of the two hypotheses in order to contradict one of them.
Starting with the transmutation hypothesis, its opponents have to admit that they have not been successful in finding even a single contradicting fact after nearly a decade since its revival. Objections to the hypothesis are not lacking, but most of them are not really directed against it, but only against the Darwinian theory on which it is based – a conflation that cannot be condemned enough. Objections relating directly to the transmutation hypothesis have never provided refuting facts and have resorted to protesting its indemonstrability. Such protest is a logical mistake.
Negative refutations, like those emanating from paleontology, are also inadmissible. To those belong the arguments stating that if the transmutation hypothesis is correct, then intermediate forms connecting the species (both in the sense of closely related species and in the sense of higher groups, orders or classes) in different strata must be found. This postulate is correct: according to the transmutation hypothesis, these intermediate forms had to exist, and it has to be considered a priori probable that several of those have been preserved in fossil strata.
Darwin showed how relatively scant are the remains left from the extremely rich animal world of earlier epochs, and that it is illegitimate to draw negative conclusions from paleontology, i.e., to conclude from the absence of remains that postulated animal forms did not exist. Although apparently only a small fraction of the extinct animal world could have been preserved in conditions that allow fossilisation, and although only a very small part of this fraction is accessible (as only a fragment of the landmass and nothing of the sea has been researched for fossil remains), it is now nevertheless possible to demonstrate transitional forms in both senses. Thus, the argument that those transitional forms are missing must be abandoned.
Paleontologists have rich and abundant material to work with, so they should have no difficulty finding many transitional forms between related species. New work related to this point has been published recently. It concerns a snail species of the genus Planorbis, found abundantly throughout the Steinheim basin. HilgendorfFootnote 10 distinguishes 19 varieties that are so markedly different from each other that, if they were to be displayed separately without the connecting transitional form, they would be considered different species. Each variety is located in a well-defined area of the sediment, and in fact they are arranged one on top of another according to their relationship, and the main forms are connected through transitional forms that appear only in the border zones. We have in front of us the developmental history [Entwicklungsgeschichte] of a species stretching over many centuries.
Thus, the desired transitional forms between species are present, if one only makes the effort to find them.
That said, transitional forms between the big groups of the animal kingdom have already been found. We have obtained the imprint of an animal in one plate from Solenhofen quarry, which connects the well demarcated class of birds to the reptilian class. The famous Archaeopteryx can be termed neither a reptile nor a bird, since it bears characteristics of both classes: it has the simple tarsus, the leg, and the feathers of the birds, and the pelvis and the long tail-spine of the reptiles. Shortly before the discovery of this strange fossil one of the most biased followers of the creation hypothesis, Andreas Wagner, said “a reptile with the wings of a bird would be a monster, which is imaginable in fantasy but not in nature.” A few months later, he himself had to introduce Archaeopteryx to the Munich academy. It was obvious that he felt this discovery did not fit his views, as he vigorously disputed the Darwinian interpretation of this fossil. Even Giebbel could not find a way to tackle Archaeopteryx, other than to declare it as an artifact, a fraud.
In light of the above, it is certain that so far no facts decisively contradict the transmutation hypothesis, while one cannot say the same for the old creation theory. There are numerous conflicting and refuting facts with regards to the creation theory.
First, I consider the known case of the embryonic teeth-germs of the cetacean. It is impossible to imagine that creation theory would advocate a purposeless creator, since it is necessarily a purely teleological theory. What purpose do the teeth-germs serve in whales if we know that they will never become teeth? I am familiar with the explanation that these teeth-germs are part of the mammalian body plan, but this does not solve the contradiction.
In the same category of facts are the well known leaf-like appendages of the embryo of the water slater (Asellus aquaticus), which suggest that these appendages originated from a species with leaf-like appendices, just as the teeth-germs of the whale embryos suggest a toothed-mammal ancestry. In Asellus the teeth rudiments have no function,Footnote 11 and do not belong to the type of the animal, and thus cannot be explained with a plan. This is also the case with the larva of Mysis and Lygia, which sheds its skin already in the egg. This skin has no functional significance, and it does not belong to the design of these animals, just like the case of the Amphipodan micropyle. All these structures need to be understood as historical documents, which reveal to us to some extent the historical origin of a given species.
Late developmental history offers refuting data as well. The reverse metamorphosis [rückschreitende Metamorphose] of many parasites, of which the interesting history of the origin of the operculum [DeckelFootnote 12*] of SerpulaFootnote 13* was communicated by F. Müller,Footnote 14 are examples which I only want to mention, without discussing details.
A plethora of well known anatomical data is in glaring contradiction to the creation hypothesis: the vestigial shoulder girdles of the slow worm and other lizards, and also the vestigial pelvic bones of the whales. No one can argue that these parts are in any way of use to these organisms. They are there, it is argued, in order to allow the emergence of the so-called body plan [bauplan].
Why then are the snake's shoulder and pelvic girdles, which possess the same body plan as other closely related lizards, missing completely?
The answer that extremities are not part of the snake's body plan is wrong, since a small group, the constrictors, has vestiges of hind limbs.
From what was said up until now, it follows that the old creation hypothesis does not provide what a scientific hypothesis should provide because it is in complete contradiction to the facts. Therefore it does not have any scientific merit and one can discard it henceforth.
We reach the second part of this analysis: the theory that Darwin established relying on the transmutation hypothesis when he was searching for the physical causes of the transmutation.
If it were possible to discover forces that necessarily generate a constant change of species, then the transmutation hypothesis would be elevated to a state of almost certainty. We thus ask whether the physical causes for transmutation suggested by Darwin do exist, and if so, whether they necessarily produce effects similar to those assumed by the transmutation hypothesis.
Darwin deduces that new species originate from pre-existing ones through very inconspicuous causes, namely the small differences by which one individual is distinguished from another. Darwin bases his theory on breeders’ experiments showing that such small peculiarities can be reproduced and accumulated so as to allow the emergence of new breeds that are highly divergent from the original species. The accumulation occurs through artificial breeding, in which only those individuals that have exactly the desired peculiarities at a given moment are bred. Many of those strangely designed pigeons, chicken, sheep and pig breeds (typically found in England nowadays) owe their existence to artificial breeding.
Darwin shows that a rather similar process has to occur in the wild, where external conditions replace man. Therefore he defines natural selection as the accumulation of individual traits that generate new breeds. This is the result of the fact that all organisms have to struggle for existence in a process whereby all useful individual peculiarities are preserved and accumulated through heredity, while deleterious peculiarities are lost.
Natural selection, therefore, differs considerably from artificial breeding, since only characteristics that are useful in any way in the struggle for existence are preserved and strengthened. This is the basis for dubbing the Darwinian Theory as the usefulness theory: it is the effect of the struggle for existence, based on species’ variability, through which natural selection generates new races.
So far, Darwinian thought appears indisputable, even to its opponents such as B. Bischoff.Footnote 15 The variability of species stands firm, and the existence of a law of nature, which Darwin summarized under the catchphrase of the struggle for existence, cannot be denied. As soon as these two factors are accepted, natural selection necessarily follows, and this means the development of new races.
The current data supports this theory up to the race level, yet there is no reason to assume that the effect of the law of nature [natural selection] is limited to this level alone. Quite the contrary: this trend will continue; each newly formed race will deviate from the original stock and will eventually become an independent species.
Following Darwin, if we assume that organic life stems from several simple organisms, then both the modern and the historical living world can be derived from them by implementing natural selection.
Darwinian theory has been challenged with the argument that it may explain the formation of many varieties, which merge into each other, but that it cannot account for the emergence of modern species that constitute well-demarcated groups containing similarly designed individuals. It has been suggested that Darwinian theory “would lead to a chaos of forms” [Formchaos], which in reality does not exist.
I am convinced that I can demonstrate this is not the case. This chaos of forms would be the case if the adaptation of a species to new living conditions through natural selection were to be swifter than they are in reality.
Assuming, for the sake of the argument, that adaptation occurs in the course of a generation while keeping step with reproduction, and assuming constant change in the conditions of life, then an animal that has ten offspring annually would produce a new variety every year, and this variety is represented only by those ten individuals. Thus, after five years, 1,100 varietiesFootnote 16* would have been produced (each represented by ten individuals). Further, if we were to assume that each individual of the ten offspring is itself able to become a new variety, then the number of varieties would equal the number of individuals in the population. This clearly is a state of chaos of forms, a situation that does not exist at all. This assumption is utterly flawed, since adaptation does not keep step with reproduction, but progresses considerably more slowly. Even the most variable animal forms will acquire a new adaptation only over the course of thousands of generations. Long before a new adaptation can appear, millions of individuals of similar form must co-exist. Thus, new adaptations will not affect only a single or a few individuals, showing that adaptations do not emerge abruptly, but only over many generations.
By meticulously following the Darwinian theory we necessarily reach an understanding of the living world as it is in reality. It inevitably follows from Darwinian natural law that varieties and species are built roughly in the wayFootnote 17 we see them in reality. Species are sometimes more and sometimes less sharply distinguished from each other, depending on whether the transitional forms have survived the struggle for existence. A species is comprised of a different number of varieties, depending on the degree of its variability and on the intensity of competition with other species during the struggle for existence. The formation of genera, too, is an inevitable part of our discussion, since all the species derived from a common ancestor are more closely related to each other than to any other species, and the same applies to families, classes, and orders. In short, we learn to appreciate as a necessity the unique and intricate kinship relationships in the organic world, which is scientifically termed “the natural system.”
While the Darwinian Theory teaches us why another world of organisms lived in earlier periods on earth, it also shows us that its principles necessitate a continuous change of species, thus providing us with a clear explanation for the extinction of species. A species cannot live forever, since new races and species constantly originate and compete with it. This alone demonstrates how living conditions are in constant change. Either a species adapts itself to new living conditions, and then mutates into a new species, or it fails to do so and becomes extinct. In both cases the species as such disappears from the realm of living forms.
It is evident that Darwin's natural laws of the struggle for existence and of natural selection are to the transmutation hypothesis what Newton's general gravitation is to the heliocentric hypothesis. With certain premises, the existence of a gravitational force necessarily leads to the movements of the heavenly bodies as assumed by Copernicus and Kepler, and thereby this assumption becomes close to certainty. Similarly, the existence of the Darwinian natural forces leads to the changes in living forms that Goethe, Lamarck, Oken, and Geoffroy proposed, and this assumption too will raise the hypothesis to the same high degree of probability.
However, in both cases, the investigated natural forces operate only under certain presuppositions, and not all the causes of these phenomena are revealed simultaneously with the observed phenomena themselves
The movement of heavenly bodies does not depend solely on gravitation, and a primitive impetus that provides them with a tangential motion must be assumed. Similarly, in the movements of the living world (as revealed to us through the origin and demise of species) the variability of organisms – or more precisely the hereditary capability and variability – is the essential premise. Hereditary capability transmits the parental plan to the offspring, and variability is responsible for the deviations from that plan (without it, the gradual change of a species into new species would not be possible). In a way, variability provides the material for the action of natural selection by producing large amounts of small variations from which natural selection chooses the useful ones.
Natural selection by itself would not be able to bring about the formation of new species, just as gravitation by itself would not be able to assign the earth an elliptical orbit around the sun; variability must be added here, similar to the tangential impetus there.
Future research on the origin of species should mainly focus on answering the question of the nature of variability.
If we try to comprehend the nature of the vital activity [that leads to variability] of organisms, it is clear that it is closely related to the hereditary capability.
The latter is usually defined as the capacity of organisms to transfer their characteristics to their descendants. I believe, however, that heredity is the communication of a very specific developmental direction to the germ of the organism through the mixture of its components;Footnote 18 the same developmental direction is possessed by the parental organism at the beginning.Footnote 19 Thus, under completely equal external conditions, the parent and the descendant organisms have to pass through the same developmental stages.
If we recognize that the capacity for inheritance is the transmission of a developmental direction, then explaining variability becomes easy. It is obvious that external influences are never absolutely equal in the development of two organisms: from the first formation of the egg onwards, different influences slightly deflect the developmental direction (transferred through heredity) toward different directions. Thus, the developmental end result cannot be identical between parents and offspring, and in each living stage small variations in their form distinguish them from each other.
Accordingly, variability is nothing more than the result of the inherited developmental direction and of external influences, so that the final impetus to speciation has to be found in heredity and in external influences. External influences exert a two-fold effect: first as a force modifying heredity and producing individual features, and second, to a certain extent, as a regulator of the generated variations, i.e., natural selection.
Even if it appears certain that external influences (which are different for every individual) slightly deflect the inherited developmental direction and give impetus to individual differences, it is by no means proven that there cannot be internal causes for the emergence of such differences in addition to the force that is modifying the ancestral developmental direction.
Darwin acknowledges this possibility by writing that “individual differences are probably the only ones which are effective in the production of new species.”
It is imaginable that within organisms there is a force through which they change their gestalt in the course of numerous generations and transmutate into a new species. It necessarily follows that, after a while, out of a certain species one or several new species (equally demarcated) have to emerge. Thus, the entire animal and plant kingdoms inevitably had to evolve into their modern gestalt from the lowest organisms. The organismal world could not (assuming there was such a force) develop differently, just as something other than a pigeon can come out of a pigeon's egg!
However, this contradicts the facts. Humans can arbitrarily produce new races through artificial selection, thereby redesigning the organic world (even if only to a limited extent), but this would not be possible if only a single organic world, devoid of modifications, were possible. Anyway, we are not allowed to invoke an unknown force when we can have a sufficient explanation of these phenomena with known forces, or still hope that future research will provide one.
For this reason, I also disagree with the principle of perfection,Footnote 20 as advanced by Nägeli. It definitely is not required in order to explain gradual structural complexification from the lowest to the highest organisms. Not only does the utility principle suffice in this case, it can also account for the gradual decomplexification most strikingly seen in parasitic crabs [Schmarotzerkrebse].Footnote 21*
However, there are other phenomena that demonstrate the insufficiency of the utility principle. Nägeli reasonably stresses that, especially in the botanical domain, purely morphological characteristics (e. g., leaf arrangement) frequently display notable constancy. According to the utility principle, this constancy can exist only for useful traits, i.e., physiological important characteristics.
Such examples are found in the animal kingdom as well. The fine markings on the butterfly wings, which frequently show a striking constancy down to the smallest details, are of hardly any physiological value. Another example is the scales on the head of the snake, which likewise show constancy in number and position in a given species.
These examples demonstrate how until now only a single aspect of speciation has been considered, and that yet another factor should be considered, one that is self-evident (and this is why it has been overlooked so far). I believe this second factor is none other than the specific nature of organisms, their unique chemical and physical body composition.
A given kind of organism possesses certain fixed characteristics (both in number and in quality), but it does not possess all possible traits simultaneously. This seems to indicate that the organism has a limited capacity for change, since it can vary only in directions compatible with its chemical and physical makeup. It cannot therefore produce all imaginable changes, but only some, although these will still be numerous.
When it is argued that organisms could vary in every possible direction, it is based on a biased exaggeration of the Darwinian theory. By stating that there are several possible directions, one certainly admits the existence of the impossible ones.
When considering this second factor – the nature of the organisms – the constancy of the purely morphological characteristics is self-explanatory. Individual deviations originate through the influence of external circumstances on the inherited developmental direction: they are not incidental, and they could turn out differently, depending on the quality of the external influences and on the nature of the individual. The same influences can simultaneously cause both useful and important physiological deviations, and deviations that are physiologically neutral and purely morphological. These deviations are the reaction of the organism to specific external influences, and both kinds of deviations are simultaneously and interdependently generated. Both types will be maintained and both will reach the same stability, because they are internally connected.Footnote 22
Applying the utility principle to the issue of creation would make it seem like a mere accident and not as a necessity, as we understand it. The Darwinian theory has often been accused of allowing nature to haphazardly generate [herumtappen]Footnote 23* new forms of life, but this accusation must be rejected in light of the fact that the number and kind of possible variations is determined by the constitution of each species. The direction of these variations in each organism is partly inherited and partly acquired, because they depend on the chemical and physical composition of its body. We have defined this composition as the combined result of the inherited developmental direction and the external influences that can slightly deflect them at any point. Therefore, new species must have a novel, slightly modified, capacity for variation. The greater the phyletic distance between two related species, the greater the difference in their capacity for variation, since the ancestral capacity for variation changed with every subsequent generation. It seems therefore absolutely necessary that a cat varies in a different fashion from a dog or an infusorium. This also explains why it is impossible to get from a given phylogenetic locus to any other: even after tremendously long periods associated with the most favorable external conditions, a monkey can never become an oak tree.
This seems self-evident, but it is so only when one realizes that the quality of future species is determined not only by natural selection and the struggle for existence, but also – and at least equally so – by the quality of the changing organism.Footnote 24 One must also realize that natural selection selects only from all the possible deviations, while species are the result of both natural selection and the quality of variation of their ancestors.
It seems prudent now to restate in a more precise manner the parallel between the development of the individual and the development of the entire organic creation.
From the egg of a pigeon develops a bird that we likewise call a pigeon, which is distinguished by a thousand small details from its parents as well as from all other pigeons. These individual differences are, as we have seen, the result of an inherited parental developmental direction and of external influences. Let us accept the inheritance of developmental direction: external influences as well are constantly changing, so therefore we might observe instead of the unique traits a-z, the unique traits α-ω.
In the development of organic creation we find something quite similar. In creating a new species from any ancestral species, the quality of the to-be-created species is determined by both the quality of variation of the ancestral species, and the external influences (which Darwin dubbed the struggle for existence). Here, as in the case of individual development, the selection of possible new traits is accomplished through external conditions: as soon as external influences change, a completely different species emerges from the ancestral species. The role of inherited developmental direction in ontogeny is equivalent to the role of the quality of variation in speciation. The external conditions influence both by choosing from the characteristics which are possible. It follows that had the external influences been any other than those that they actually were, then the entire organic world would have been a very different one.
Let us summarize. I first showed that the transmutation hypothesis is the only scientifically valid hypothesis concerning the origin of organic nature. Combining the Darwinian principles of the struggle for existence and of natural selection with heredity and variability (which all organisms are endowed with) necessarily leads to the creation of a living world, just as the transmutation hypothesis suggests. Therefore, the probability of the latter is increased to near certainty.
I compared the transmutation hypothesis to the Copernican theory because I am convinced that since the introduction of Copernican theory no equivalent contribution has been made to human knowledge, that is, until the publication of the Darwinian theory.
Back then, new domains that were previously unexplored were opened up for research. Similarly, today, new territories are revealed, just like after a mountaintop is conquered, and many thousands of human researches will not suffice to explore the new domains. We are not standing at the end, but rather at the beginning of the science of organic life, as demonstrated most vividly by the Darwinian Theory, which – like all big discoveries – has effects reaching far into the future. The Darwinian Theory gives us a new insight, but first and foremost it opens before us new prospects.
Appendix
On the influence of migration and spatial isolation on speciation
In his work Die Darwin'sche Theorie und das Migrationsgesetz der Organismen, Moritz WagnerFootnote 25* [1868 and Reference Wagner and Laird1873] claims that natural selection is not sufficient for explaining the origin of species. He claims that the effectiveness of natural selection demands several prerequisites: migration of the organisms, spatial segregation, and isolation. Early observations of the fauna of oceanic islands made by Darwin, as well as more recent examples communicated by Wagner, show that the migration of organisms has a paramount influence on speciation. Nevertheless, I believe that by considering it a necessary prerequisite for speciation, Wagner attributes too dominant a role to his migration principle. The basic premise of Wagner's view is correct: the generation of a new species can only be achieved through continuous prevention of crossing with the progenitor. However, absolute separation from the progenitor cannot be achieved through isolation due to migration!
Consider the simplest example, in which a single couple of a sexually reproducing species is isolated on an island. One individual has an exceptionally unique trait that probably will be passed on to some of their descendants, but definitely not to all. The other descendants will resemble the progenitor, and crossing of the modified descendants with the unmodified forms (which means crossing the incipient variety with the progenitor) is inevitable. According to Wagner, a new race or species could not be thus formed, since crossing with the progenitor poses an insurmountable barrier. Also, in the aforementioned case, no new species would be formed if we assume that both forms (the modified and the unmodified) were equally equipped for the new conditions of life. Two possibilities are then imaginable: in one both kinds could live next to each other in relatively similar proportions. The second option is that there will be a fusion of traits, culminating in the emergence of a new species, which is distinguished from the progenitor by an insignificant trait.
Further development of this insignificant trait, by accumulations or enhancements of it, consequently leads to the generation of a new race or species. However, this can happen only if the modified trait (which other individuals lack) supplies its bearer with an advantage in the struggle for existence. The carriers of the advantageous traits will increase in numbers (both absolute and relative) as crossing with the unmodified individuals becomes rare (due to a diminished proportion of the latter), and the advantageous traits will accumulate further.Footnote 26
Thus, in this case, natural selection prevents crossing with the majority of the progenitor population, and in no way is it [the result of] isolation.
It would appear that natural selection depends on the preliminary action of both isolation and emigration (of individuals who originally made up the new population): the more complete the isolation and the fewer the emigrants, the more they contribute to natural selection.
There is only a minute difference between speciation through natural selection in the original habitat and in an isolated migration-site. As has just been demonstrated, even under the most favorable conditions of isolation, totally preventing crossing with the progenitor is not possible. Some of the descendants from the first couple will always resemble the progenitor and will lack the unique traits of one of their parents. The larger the number of the original colonists, the larger the number of unmodified individuals to begin with, and the longer the process of selection on these unmodified individuals. This selection process can be accelerated or decelerated substantially as a consequence of the size of the migrating colony, but it cannot be changed or stopped. When half of the colony migrates and is modified, why could those that remain not become modified as well to produce a new species if the opportunity presents itself?
Wagner is decidedly mistaken when he suggests isolation through migration as a necessary prerequisite for speciation. This is readily demonstrated in the highly meticulous research of Hilgendorf, which showed that over time Planorbis multiformis in the same fresh-water lake successively passed through nineteen different forms with no migration. There are numerous other facts that speak against Wagner's views.
I have previously asked myself if a species with populations that share the same habitat could split into two new species. A priori, since we do not argue (as Nägeli did) that there is only a single most adapted form, such a split is possible according to the utility principle, since an animal form can adapt to a change in its living conditions. Even on its own, the evidence speaks for it; let us consider first geographical distribution.
Especially striking is the example of butterflies, where frequently several closely related species of a genus possess roughly the same distribution range, as is the case with Vanessa polychloros and V. urticae, Limenitis populi, L. Sibylla and L. Camilla, Apatura Iris and Ilia, Satyrus Proserpina and Hermione, Pararga Maera and Magaera, and many others. Lay field observation has demonstrably described aptly these relations as “large and small”: large tortoiseshell [Nymphalis polychloros] and small tortoiseshell [Aglais urticae], Kingfisher [Eisvogel], the Deilephila elpenor [(mittlerer) Weinschwärmer], etc., and it is possible (in some species) that individual size differences might indeed have caused a split from the progenitor. It is possible that in butterflies the marking and coloration of the flight organs alone is sufficient to distinguish closely related species. Such is the case with certain color shades that determine sexual selection for mating, as was indicated somewhere by Darwin.
Undoubtedly, sounder examples of the divergence of species in the same habitat are available. I need only mention F. Müller's olfactory and grabbing forms of male Tanais dubius,Footnote 27 or the three female forms of the Papilio memnon, distinguished by color and form. Another example is dimorphism appearing in early developmental stages, as in the two and three forms of caterpillars in several butterflies, an extremely odd and not well understood phenomenon. Every entomologist knows that the caterpillars of Chaerocampa elpenor [elephant hawk-moth] can be black, brown, or green, and that all three forms, regardless of sex, are commonly found at a single spot. The situation is similar with the caterpillars of the oleander hawk-moth [Daphnis nerii], Chaerocampa nerii, and two kinds of forms of caterpillars of Sphinx convolvuli [convolvulus hawk-moth], Smerinthus tiliae and Macroglossa stellatarum, which are known to me.
Therefore, a species, as well as a single sex or a single developmental stage, could thus split into several forms [in the same place].
This also proves that a species can produce new races without migration. The opposite can be proven as well, i.e., that migration – even if accompanied by a complete isolation of the colony – is not sufficient to force a species to change. The Vanessa cardui [painted lady] and the Vanessa atalanta [red admiral] butterflies probably prove this best, since they are distributed globally. Individuals living in America are absolutely protected from crossing with European individuals, and yet they have not changed. It is plausible that occasionally some individuals will be brought by ship to America, but this allows only a negligible level of crossing with the progenitor, certainly not to the extent of preventing change. Crossing several European individuals with the vast quantity of American individuals generates only a small permanent effect, no different from that suggested by Wagner who pointed out that selected bulls or stallions can become improved by breeding with the semi-wild cattle of the South American steppes.
I have tried to show that neither the migration nor the isolation of a colony are a necessary prerequisite for the change of a species, and therefore the so-called migration law must be refuted, as Darwin himself did in his correspondence with Wagner (even if more in a factual than a formal manner).
Since, as we have seen, isolation is incapable of preventing crossing with the progenitor (because a proportion of the isolated individuals and an even bigger proportion of their descendants must always belong to the unmodified type of the progenitor), we have to ask what other agents cause the striking effects of isolation. Why do we find on the oceanic islands peculiar fauna with many endemic species? How is it we find quite similar relationships on the isolated volcanoes of South America? Or in other words, why have the immigrants, in most cases, transformed into a new species in such isolated habitats?
One cause of this is surely a consequence of the highly idiosyncratic conditions of life met by the immigrants in these habitats. The composition of an animal and a plant group is always very unique, because it occurs only in a given habitat. Thus, the struggle for survival is different for every newly invading species.
I think that the trigger for change is to be found in the aforementioned reasons, and that the origins of the numerous local species of such isolated habitats are thus explained. We can accept that the process of natural selection is substantially favored and accelerated by spatial isolation, even if not principally promoted by it. If necessary, it is possible to demonstrate this argument mathematically, but it already follows from my discussion of the effects of isolation. Natural selection works to prevent continuous crossing of the advantaged variety with the majority of individuals of the progenitor by continuously diminishing the population of the latter to the point of extinction. When we realize this point, it becomes clear that the period required to achieve this goal depends on the initial ratio of the variant and progenitor individuals. When one hundred individuals emigrate to establish a new colony and only one of them has a special trait that is advantageous for the new living conditions, then the generation of a new species by the descendants of this individual is protracted compared with the situation where only two individuals establish the colony and one of them possesses the advantageous trait.
Therefore, the rate of transformation of a species in an isolated region depends on the initial number of emigrants. The rate of transformation will also be slowest when there is no isolation, and with partial isolation it will be hindered. In the latter case, on the border between the two colonies, we may expect transitional forms, which are rightly described as geographical intermediate forms between the new colony and those in the ancestral habitat.
Summarizing, we see that spatial isolation works first by providing the impetus for change, and then by promoting this change, culminating in the end product – the new sharply demarcated species – and it does so by preventing the formation of geographic intermediate forms. It is important to explore how isolation takes place in general, and how different degrees of it influence the form of a new species, the level of demarcation from the progenitor, and the fairly complete suppression of geographic intermediate forms.
The means by which relatively complete isolation is achieved are very diverse. The sluggish locomotion of a species ensures its relative isolation: species of snails and moles owe their wide distribution to the uniformity of their living conditions, which means they lack the impetus for change.
I would like to draw attention to a mode of isolation which occurred to me this summer through my studies of Lepidoptera. Apparently, for all animals intimately associated with plants (especially insects), spatial isolation can be caused by expansion of the plants to different altitudes. Crossing with the majority of the progenitor population is prevented in this case by the fact that higher altitude plants are dormant for a longer time. Thus, their symbiont insects reach sexual maturity later, and reproduce when individuals of the lowland population have already completed their reproductive cycle and died. A case in point is certain butterflies, which have close relatives in high ranges.
Erebia Medusa [the woodland ringlet] is on the wing near Freiburg in May and early June in the lowlands, while the closely related Erebia stygne flies roughly one month later (when the woodland ringlet is no longer seen) at altitudes of 1000 to 5000 ft. [~300 to ~1500 m] above sea level. Although in some places the two species overlap, this does not contradict the assumption of common descent, since each demarcated species tries to expand and can interact with the closest relatives in the same space without the risk of blending. The fact that in the case of [E.] Medusa and [E.] Stygne the dispersal regions seldom overlap indicates that both species have not undergone very extensive migration since their appearance (i.e., they split only after the ice age).
