EVOLUTION. — Evolutionism (transformism, phylogeny, theory of descent) is the scientific doctrine that affirms the natural derivation of higher organisms from lower ones. Since paleontology teaches that living beings have appeared on earth one after another, and, on average, the most differentiated after those structurally simpler, two hypotheses are possible: either each natural species of organisms has had, in the course of time, an autonomous and independent origin (fixism); or higher species have derived from lower ones (evolutionism).
OUTLINE:
I. General Notions
II. Theories
III. Examination of Theories
IV. Evidence
V. Critique.I. GENERAL NOTIONS
The doctrine of evolution has been and is supported by all materialists and by many of the same spirits, though with different postulates. For materialists, not only are higher living beings derived from lower ones through physical-chemical causes, but these from even simpler ones formed spontaneously from inorganic matter, which, in turn, is eternal and uncreated; even the human soul would derive, through transformation, from the soul of brute animals. For theists, matter is the effect of a creative act of God; the first living beings, according to some, would have originated through spontaneous generation, while according to others they too would have been created by God in one (monophyletism) or more specimens (polyphyletism), from which all the species subsequently appearing in geological periods would have originated. For theists, the human soul is created directly by God; the body, instead, derives from the body of an anthropoid.Evolutionism, as supported by materialists, is unacceptable because it contrasts with certain scientific data (for the philosophical errors of materialism, V. MATERIALISM). That matter is eternal is contrary to the second law of thermodynamics, inasmuch as, if this were so, absolute disorder and complete immobility would now prevail in the universe, since all dimensions that render energy usable would already have disappeared. If, therefore, matter began to exist in time, it is created. That the first organisms formed through spontaneous generation (we too use this expression, though it is quite inexact) is contradicted by the experiments of Redi, Vallisnieri, Spallanzani, and above all Pasteur, with regard to known organisms; and if one were to suppose that the first living beings possessed a structure much more elementary than the most elementary organisms known to us today, the question of how their direct formation from matter was possible is gratuitous in its first part and, in its second, contrary to the laws of probability, since, however simple they may be supposed to be, those primitive organisms would still have to possess a heterogeneity and asymmetry (with respect to inorganic matter) such as to constitute an event highly improbable in theory and practically impossible to occur in nature. That evolution has not been brought about solely by physical-chemical forces is contradicted by the certain data of paleontology, which demonstrates that, on average, there has been a continuous progression of living forms, with the production of organisms always adapted to their environment; whereas, if evolution were true, there should be, among the many forms that have succeeded one another, only a few well-adapted ones. Finally, that the human soul represents merely a further perfection of that of brute animals is contradicted, at least indirectly, by experimental psychology.
Theistic evolutionism, instead (excepting, for the reasons stated above, the group that admits spontaneous generation), is a sound scientific doctrine. As regards the extension of the transformist theory to the origin of man, V. EVOLUTIONISM.
II. THEORIES
It is necessary, from the outset, to keep carefully distinct the fact of evolution from the manner in which it may have occurred. The modalities and causes that would have determined and directed the successive transformations of organisms constitute the basis of the various theories, which may be wholly or partly false without necessarily dragging the fact of evolution down with them, since this is founded not on theories but on objective data drawn from the various branches of the science of life. In the impossibility (and, moreover, in the uselessness) of even briefly mentioning all the numerous evolutionary theories that have succeeded one another in the past hundred years, we shall at least recall the most classic ones.1. Lamarckism
Lamarck (1809) assigns two essential causes that would have produced evolution: the intimate nature of living beings, which tends of itself to evolve, and the external environment that surrounds them and influences them through temperature, chemistry, etc. The incessant modifications of the environment cause organisms to feel the need for new functions, which in turn determine the appearance of new organs suited to satisfy them, while those already existing, if they still serve a purpose, continue to develop through use; if, instead, they become useless, they atrophy through disuse until they disappear. In this way variations are produced in organisms, manifesting themselves first in the soma but capable of modifying the germ cells as well, thus rendering those acquired characteristics hereditary. Their accumulation in successive generations will give rise to organisms so different as to form new species. That intimate necessity to evolve will then ensure that these modifications always advance organisms up the scale of living beings.2. Neolamarckism
Under this name should be comprehended all those authors who, while accepting Lamarck’s theory, have overvalued the action of one of the factors with respect to the other. Historically, however, neolamarckists are those who attribute a prevailing importance to environmental factors, such as Spencer, Eimer, Cope, etc., while Nägeli, Rosa, etc., who make the evolution depend prevalently or entirely on internal factors, are commonly called upholders of the theory of “internal causes.”3. Darwinism (1859)
In a population of individuals, no two are ever found to be perfectly alike. The differences, according to Darwin, are due to the somewhat different conditions in which the germs develop. And it is not said that such differences are in every case advantageous; indeed, generally they are either indifferent or actually harmful. But, just as in breeding man selects the individuals bearing a certain character that he wishes to perpetuate, and, through suitable means, renders it stable by creating new races and varieties of animals and plants, so nature selects the individuals bearing characters advantageous to the environment in which they live, and inexorably suppresses the others. Indeed, in the struggle for existence, the weak and the unfit perish, and only the strongest survive to sexual maturity. Consequently, the advantageous characters are transmitted to the offspring and accumulate in the course of generations, leading to the formation of organisms so different from their ancestors as to be classified in a new species. The evolutionary process thus constantly tends toward a higher organization because this, as a rule, represents an advantage in the struggle for existence.4. Neo-Darwinism
A. Weismann, who first upheld a clear separation in organisms between soma and germ, denied Darwin’s assertion that the environment can in any way influence the germ. For him, the chromosomes (v.) of germ cells contain particles that he calls determinants, each of which would cause the structure of a part of the organism. The adult would thus be predetermined in its characteristics by the collection of determinants present in the nucleus of the germ cell, and no characteristic could develop if the corresponding determinant were lacking. But since germ cells multiply by division, the determinants must likewise multiply in the same way. Thus arises a whole series of these newly formed elements, which must assimilate, grow, and prepare for a new division. At this point, the struggle for existence comes into play, whereby the stronger determinants or those that by chance occupy more advantageous positions can grow more at the expense of the weak and those not favored by chance. Consequently, the characteristics dependent on them will also be more developed, and the organisms will be favored in the other struggle for existence, sustained by Darwin, between individuals. Since only these better-endowed organisms reach sexual maturity, they alone will transmit their robust determinants to the offspring, which will continue to improve in successive generations until new species are produced.5. Mutationism (1907)
While Lamarck and Darwin based their ideas on the slow accumulation over time of slight individual differences, De Vries instead argued that evolution occurs through the emergence of significant variations that appear suddenly and randomly in one or more individuals of the same species, giving rise to entirely new and hereditary characteristics (mutations). Such characteristics are sometimes so substantial that they alone can establish a new species; more often, it is necessary to wait until other variations arise in the same individuals before they can be separated from the parent species. Since these variations are random, not all are advantageous for the organisms that carry them; however, the intervention of the struggle for existence and natural selection preserves the favorable ones while eliminating the harmful. De Vries locates the cause of mutation in the influence that an unusual environment exerts on organisms, even reaching the germ cell; but here the variation remains latent (premutation) for thousands of years before suddenly manifesting itself one day without any apparent cause.6. Neo-mutationism
Many modern authors, especially geneticists, while sharing De Vries’s theory, no longer accept the existence of a hypothetical latent period between premutation and mutation. Instead, they believe—and experience confirms—that the alteration of the germ cell manifests itself immediately in the offspring.7. Oligacism (proposed by D. Rosa in 1909 and later developed in 1918). — This theory is linked to the first Lamarckian evolutionary factor, to which exclusive importance is attributed. Just as the development of an individual, from man to adulthood, is caused and directed solely by internal factors, while the influence of the environment is limited to allowing or preventing it, so too the origin of species is due to intrinsic factors within organisms. The environment is only asked to provide the general conditions that do not impede life. Therefore, species evolve even when the environment remains unchanged, and environmental variations do not affect the direction of evolution, except to produce phenotypic characteristics that are not transmitted to offspring. Moreover, just as the adult organism derives from a single egg cell that divides into two daughter cells, which in turn divide into two more, and so on, producing increasingly different cells from the original egg cell, so too a single ancestral organism has given rise, through dichotomous division, to other species that gradually become more differentiated. However, in the dichotomous division of species, one branch is precocious and the other is delayed; the former reaches its peak sooner but produces fewer species and retains a simpler structure (persistence of lower forms); the latter, in its slower development, achieves a more complex organization and gives rise to a greater number of further branches.
This theory is still upheld by several Italian biologists, while abroad it is accepted by very few scientists. Among other theories worth mentioning are Smuts’s holism, Lloyd Morgan’s é. emergee, and Bergson’s é. créatrice.
III. Examination of the Theories
It may be useful to briefly indicate the main objections raised against the theories discussed.7. Lamarckism
That the environment can induce modifications in an organism is an incontestable fact, just as it is certain that the use of an organ leads to its greater development or its atrophy. But are these acquired characteristics transmitted to offspring? a) It is not clear how they could be. Indeed, germ cells are part of the organism just like any other body cell; now, the greater or lesser development of a muscle, for example, does not affect the germ cells of the eye at all; why then should it influence germ cells? Perhaps through special substances produced by altered organs and reaching the germ via the blood or humors? But these hypothetical substances would have to be so specific to each organ and part of an organ as to justify the asserted reproduction in offspring of the same structures acquired by the parents; which, even theoretically, seems at least excessive. b) Moreover, all the experiments conducted for decades and by every means at our disposal to demonstrate the heritability of acquired characteristics have either yielded openly negative results (the vast majority) or have had such uncertain outcomes as to preclude any affirmative conclusion at present.8. Darwinism
Darwinism starts from the slight differences found even among the most similar individuals, called fluctuations by modern geneticists, and argues that natural selection acts on these, preserving the organisms best adapted to their time and place, thus leading to a progressive accumulation of small differences. Now, this is gratuitous, if not contradictory to the scientific data in our possession. a) First of all, the effects of artificial selection cannot be equated with those of natural selection, since the formerThey lack the intelligence and the means that would enable man to isolate and cross-breed individuals bearing a given character. b) Natural and artificial selection, moreover, do not in reality produce anything new, being limited to conserving and bringing to light what already exists; they are therefore an insufficient factor for explaining the appearance of new forms. c) Furthermore, fluctuating characters are not transmitted to the skin, which inherits only the variability proper to the species; indeed, nature tends to conserve, in preference, those individuals that deviate least from the average type: the very opposite, that is, of what Darwin affirmed. d) Finally, it is not clear what real advantage could have accrued, in the struggle for existence, to the few organisms endowed with a very slight favourable character, in comparison with the numerous others lacking it and in comparison with the formidable destructive forces of the environment and of natural enemies. All the more so since the supposed advantage was limited to similar organs in which that favourable character was developed; so that all the young (in whom it was practically absent) should have perished in the struggle for existence.
9. Mutationism
Can mutationism explain the above? It does not seem so. a) Non-lethal mutational variations concern small characters which, if they can account for the formation of races, varieties, or even systematic species, are quite insufficient to constitute the larger groups; they produce, that is, a micro-evolution admitted even by the fixists, not macro-evolution. b) Nor is it seen how they can determine the latter. So far as we know, mutations that occur in nature are relatively very rare. Now, of these we must subtract 80–90% which cannot be considered a factor in e. since they prove to be regressive in relation to the vitality of the organisms, giving rise to individuals that are little viable or even pathological, incapable of sustaining the struggle for existence. Of the few that remain, we must still disregard those that are indifferent, to concentrate on the very few that are advantageous. But even these latter are generally recessive, and will therefore have to be present in both parents if they are to manifest themselves in the offspring. What probability, then, has one of these extremely rare mutated organisms, lost in the midst of an entire population of normal individuals, of crossing with another organism bearing the same mutation? And how is the ever-increasing e. to be explained if mutations are random, and the simultaneous, or almost simultaneous, explosion of numerous new forms so well adapted to their environment, as paleontology documents, if mutations are rare, regressive and recessive?10. Ologenism
This is undoubtedly a very ingenious theory; but, from the speculative point of view, it is not clear why the germ-plasm should always and only divide dichotomously (the comparison of the e. of species with the ontogeny of the individual must be regarded as purely metaphorical); and, from the point of view of the facts, paleontology does not confirm, except in a few cases, the dichotomous succession of animal and vegetable forms.Nevertheless, these and the other theories already devised, and those that may be formulated in the future, may be in part or entirely false without necessarily prejudicing the doctrine of e., the existence of which must be discussed on the basis of the facts available, not of the theories. These are now numerous and constitute the proofs of e. The principal ones will be briefly indicated.
IV. Proofs
Organisms, as anatomy and comparative physiology teach, are generally composed of cells, the number of which varies from one (protozoa and protophyta) to very high figures (metazoa and metaphyta). The form of these cells may differ, but this does not create a difficulty for e. since even the cells of one and the same higher organism are different, though all derive from a single ovum. In such diversity of form, the structure (all are composed of cytoplasm and nucleus), the chemical composition (protein substances), and the functioning (all feed by intussusception, grow, multiply, age and die) are fundamentally the same in every cell.Striking similarities are also found at levels above the cellular. If, for example, we compare the skeletons of vertebrates, we find the same bones, the same reciprocal relations, the same manner of formation, etc. Now, in the evolutionary doctrine that derives all living beings from one or a few ancestral forms, do these undeniable resemblances not find a natural explanation, at least proximate, scientific and satisfactory?
All the more so since embryology confronts us with other facts that are, and seem, rather reluctant to be explained by the fixist hypothesis. For this reason someone like E. Haeckel, borrowing from other authors but specifying it better with his fundamental biogenetic law, has pointed out that higher organisms, in their ontogenetic development, rapidly traverse those same stages that were the phases of the e. of their species; so that today ontogeny is the recapitulation of phylogeny. A particular case in point is the branchial arches of vertebrates. It is well known that adult fishes breathe by means of gills, disposed laterally just behind the head: water enters through the mouth and passes out through the gill slits where the dissolved oxygen is extracted for respiration. The rudiments of the gill slits appear fairly early in the embryo, but only after numerous differentiated processes are the gills formed so as to function. Now, in the embryos of reptiles, birds and mammals (which in the adult state breathe by lungs) the rudiments of the branchial arches appear. The branchial stage is thus transitory in them, whereas it is definitive in fishes, as Haeckel’s law requires.
Present-day birds are all without teeth; yet in the embryonic development of some the dental rudiments appear and then regress. In evolutionary interpretation the fact is well explained by recalling that the first birds (Archaeopteryx) had very powerful teeth, as paleontology attests.
To confine ourselves to one last fact from embryology, we may recall that the adult blind-worm is without limbs, whereas their rudiments are present during ontogenetic development. There seems at present to be no better interpretation than to trace the blind-worm genetically back to ancient reptiles, all of which were provided with limbs.
Other proofs are furnished by systematics. So similar in the fundamental element (cells) from which they are formed, and so gradually progressive in assuming an ever greater differentiation during embryonic development, it is not surprising (but it is a new proof for the evolutionary doctrine) that adult living beings should be classifiable by the systematist in an ordered scale that continues unbroken from the protozoa to man through a whole series of intermediate organisms. If living beings have been derived one from another, this fact is not only explained but imposes itself as an absolute necessity.
The examination of present-day and fossil living beings gives us another proof with rudimentary organs, i.e. organs that are present even today in individuals but in a rudimentary or involuted form, whereas they are well developed and functional in other organisms systematically lower or chronologically more ancient, thus proving or at least suggesting a genetic derivation of the former from the latter. Examples cited are: the eyes of the mole, the bones of the hind limbs of the whale, the splints of the horse, and many others.
Certainly, in order for transformism to derive an argument from systematics, it must still be demonstrated that living beings appeared on earth in the order in which they are placed by the classifier; otherwise, the gradation of organisms could not be explained evolutionistically. Well, it is precisely this that the study of fossils tells us. Paleontology, in fact, teaches with absolute certainty that types, classes, and often even orders appeared not all at the same time, but one after another, in the order of progressive anatomical-functional differentiation required by the theory; so that the present gradation of living beings revealed to us by systematics corresponds, on average, to their actual composition over time. Not only that, but if today types, classes... are clearly separated in such a way that it is difficult to connect them genetically, paleontology indicates fossil forms that constitute the bridge of passage between the lower and the higher, such as, for example, the archaeopteryx, a connecting link between birds and reptiles.
Moreover, in some well-established cases, paleontology presents all or almost all the terms of transformation through which an organism has passed in geological periods before reaching its current form (orthogenetic series). Take, for example, the series of equids, in which, from the beginning of the Eocene to the Pliocene, one witnesses a progressive increase in size from that of a hare (e.g., Eohippus) to that of our horses; and a progressive reduction of the toes. The Eocene Eohippus still has 4 toes on the front feet and a splint bone (corresponding to the 5th toe); 3 toes and 2 splint bones (corresponding to the 1st and 5th toes) on the hind feet. The Oligocene Mesohippus has 3 toes on the front feet and one splint bone (corresponding to the 1st toe), while the rudiment of the 5th toe has already disappeared; and 3 toes without splint bones on the hind feet. The Pliocene Neohippus has barely 3 toes per foot, and of these only the middle one, having become very robust, reaches the ground; the others (the 2nd and 4th) regress until they are reduced to the splint bones of present-day horses. Is this not good evidence in favor of evolution?
Other similar arguments could still be drawn from paleontology itself, from biogeography, and from genetics; but they would be only new confirmations that add nothing directly to the fundamental structure of the proofs of transformism. It will not, however, be useless to briefly and summarily examine to what extent the facts adduced demonstrate this doctrine.
V. CRITIQUE
Although many authors attribute to the above arguments the value of authentic proofs, so much so that they consider evolution as now demonstrated, others, fewer perhaps but certainly more objective, prefer to regard them as mere indications, and moreover expressly declare that these must be considered together and not one by one to derive any satisfactory proof. This is, at the present state of our knowledge, the safest position, for in reality the individual arguments either do not withstand calm criticism, or are evolutionary interpretations of facts in themselves indifferent, or at most testify to a transformation of organisms far more restricted than that which is intended to be proved; their totality demonstrates only that evolution may have occurred.Here, in fact, is the logical procedure of convinced evolutionists: if evolution has occurred, they argue, organisms must present the following characteristics: they must all fundamentally possess the same anatomical-physiological structure; in development, the higher ones must temporarily pass through stages that are definitive in the lower ones; they must be classifiable by the systematist in a progressive ascending scale; the higher ones must appear on earth after the lower ones, and in particular the higher after the lower. Now, comparative anatomy and physiology, embryology, systematics, and paleontology respectively demonstrate all this. Therefore evolution has occurred and the fact of evolution is certain.
But in good logic, the conclusion seems illegitimate. While it is correct to affirm that, if evolution has occurred, these facts must take place (otherwise we should have proofs to the contrary!), from the existence of these facts one can only conclude that evolution may have occurred; the existence of these facts and indications is the indispensable condition for the doctrine of evolution to be scientifically tenable; but to pass from its possibility or probability to certainty, the proofs are still lacking.
Having thus illustrated the intrinsic logical weakness of evolutionary reasoning, let us turn to the examination of some facts that form the premises of the above syllogism.
With regard to the arguments provided by comparative anatomy and physiology, it may be answered that even chemical bodies fundamentally have the same structure (atomic and subatomic) and the same modes of action (laws of chemical reactions); and yet no one can confidently maintain that they are derived through successive transformations from a common primordial element more simple. Therefore this argument in itself has certainly no probative value; indeed it might serve in the hands of the fixist to confirm him in his thesis, since the only reasonable explanation of the similarity among inorganic bodies reduces to the fact that they are as they are because God made them so: the same reason advanced by fixists to explain the similarity of living organisms. Nor do the facts from embryology have greater probative value. Already the fundamental biogenetic law, as proposed by Haeckel, is repudiated by many evolutionists themselves, since comparative study does not demonstrate the resemblance of higher embryos to lower adult organisms, but only the resemblance between embryos and embryos. And this resemblance is all the greater the earlier the embryonic stage considered, so that it diminishes as development proceeds. Now, this can be attributed not to evolution but to the same mechanical necessity of formation by which Michelangelo’s Moses and Pietà (so different in the finished work) had to resemble each other all the more the closer they were to the stage of the unhewn marble block.
The alleged presence of branchial arches in the embryos of higher vertebrates is at least in part gratuitous and the result, in interpretation, of an evolutionary mentality. For these are not branchial arches but simple visceral arches that are neither gills nor ever become gills, being always destined to a function quite other than respiration. It is true that morphologically they resemble the corresponding arches from which gills will be formed in fishes; but it is equally true that
The same dental rudiments found even today in the embryos of some birds are not convincing evidence, for two reasons: first, histological study does not reveal the presence of rudiments, but at most dental ridges, which are an early formation from which true rudiments should later develop with the participation of other cellular layers; in our case, however, these never actually form (indeed, Ròse and Carlsson question whether they are even dental ridges); second, if these ridges are indeed an atavistic remnant, they raise the problem of why they do not appear in the embryos of all birds. Nor is it valid to reply that some species have evolved more than others, since here we are dealing with proving the existence of the rudiments rather than merely supposing II.
The case, finally (and those analogous to it), of the slow-worm embryo, in which limb rudiments appear and then regress to the point that the adult is limbless, may more appropriately be cited as an example of regression, not as a sign of progressive
Systematics and paleontology remain. But even here, although it is quite true that in our museums living beings are classified in an ascending order, this fact does not constitute proof of generic derivation, since chemical bodies can also be arranged in a graded manner, as Mendelejeff did with such precision that he predicted the existence of elements still unknown at the time; yet nothing authorizes us to consider them historically derived from one another in that determined order. In living beings, moreover, gradation fails precisely where it would be most needed to demonstrate evolution: in the transition, that is, from one type to another, from one class to another... Between these, there always exists a profound biological gap that neither systematics nor paleontology has succeeded in bridging. The appearance of types, classes, and often even orders is always sudden; and the failure to demonstrate the existence of even a single true connecting link is truly perplexing. *Archaeopteryx*, for example, which is always cited as a transitional form between reptiles and birds because it has the general structure of the latter and the long vertebral tail and toothed jaws of the former, does not withstand criticism, since neither the vertebral tail nor the teeth are characteristics of reptiles. Turtles belong to the class of reptiles, yet they possess teeth, whereas those of the *Jurassic* contemporary of *Archaeopteryx* were toothless; pterodactyls are reptiles found in the same lithographic limestones of the Bavarian *Jurassic* where *Archaeopteryx* was discovered, yet they had a much reduced or even absent tail.
And two other facts add to the perplexity: the not excessively rare inversions with respect to the order that would be required by transformist doctrine, and above all the simultaneous rather than successive presence of many types. In the oldest known fossiliferous strata (Precambrian), alongside unicellular beings there are already annelids, mollusks, echinoderms...
Certainly, their contemporaneity may be only apparent in the sense that, on the one hand, those strata are almost entirely unknown to us and, on the other, they lasted for millions of years, so that it is difficult to speak of contemporaneity, since the types may have appeared one after another over that vast span of time. This is a plausible supposition; but it is clear that many things in marginal hypotheses render the edifice of evolution unstable. The orthogenetic series (equids, cetaceans...) are so limited as not to justify extending the argument to classes and, even less, to types; not to mention that they do not demonstrate a progressive ascent of organisms in the scale of living beings, but only their restricted variability.
In conclusion, it may be said that the doctrine of evolution is today a good scientific theory and a useful working hypothesis, but that it is undoubtedly excessive to consider it a truth now demonstrated.