EVOLUTION. — Evolutionism (transformism, phylogeny, the theory of descent) is the scientific doctrine that affirms the natural derivation of higher organisms from lower ones. Since paleontology teaches that living beings appeared on the earth one after another, and, on average, the more differentiated after those that were structurally simpler, two hypotheses are possible: that each natural species of organism had, in the course of time, an autonomous and independent origin (fixism); or that the higher species derived from the lower ones (evolutionism).
SUMMARY:
I. General notions
II. Theories
III. Examination of the theories
IV. Proofs
V. Criticism.I. GENERAL NOTIONS. — The doctrine of evolution was and is upheld by all materialists and by quite a few spiritualists themselves, but naturally with different postulates. For the materialists, not only did the higher living beings derive from the lower through physico-chemical causes, but the latter derived from others still simpler, formed spontaneously from inorganic matter, which, in turn, is eternal and uncreated; the human soul, too, would derive through transformation from the soul of the brutes. For the theists, matter is the effect of a creative act of God; according to some, the first living beings originated through spontaneous generation, while according to others they too were created by God in one (monophyletism) or more specimens (polyphylatism), from which all the species that subsequently appeared during the geological periods would then have originated. For the theists, the soul of man is created directly by God; the body, on the other hand, derives from the body of an anthropoid.
Evolutionism as upheld by the materialists is unacceptable because it conflicts with certain scientific data (for the philosophical errors of materialism, V. MATERIALISMO). That
matter is eternal contradicts the second law of thermodynamics, since, if this were so, absolute disorder and complete immobility ought to reign in the universe today, all the dissymmetries that make energy usable having already disappeared. If, then, matter began to exist in time, it is created. That the first organisms were formed through spontaneous generation (we too use this expression, although it is so inaccurate) is contradicted by the experiments of Redi, Vallisneri, Spallanzani, and above all Pasteur, insofar as known organisms are concerned; if it were then maintained that the first living beings possessed a structure much more elementary than that of the most elementary organisms known to us today, so that their direct formation from matter was possible, the assertion would be gratuitous in its first part and, in the second, would run up against the laws of probability, since, however simple they may be supposed to have been, those primitive organisms would always have had to possess such heterogeneity and dissymmetry (in relation to inorganic matter) as to constitute an event exceedingly improbable in theory and practically impossible to occur in nature. That the evolution of the lower forms was governed solely by physico-chemical forces is also contrary to the sure data of paleontology, which demonstrates that, on average, there was a continual progression of living forms, with the production of organisms always adapted to their environment; whereas, if it were true that evolution was governed solely by chance, alongside a few highly successful forms there ought to be very many unsuccessful ones. Finally, that the human soul represents merely a further perfection of that of the brutes is contradicted, at least indirectly, by experimental psychology.
Theistic evolutionism, on the other hand (except for the group that admits spontaneous generation, for the reasons given above), is a sound scientific doctrine. As regards the extension of the transformist theory to the origin of man, V. EVOLUZIONISMO CULTURALE.
II. THEORIES. — It is necessary, from the outset, to keep carefully distinct the fact of evolution from the manner in which it has or may have occurred. The modes or 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 itself into ruin; this fact is founded not on theories but on objective data drawn from the various branches of the science of life. Since it is impossible (or, for that matter, useless) even merely to mention all the numerous evolutionary theories that have succeeded one another over these hundred years, at least the more classical ones will be briefly recalled.
1. Lamarckism. — Lamarck (1809) assigns two essential causes that would have produced the evolution of organisms: the inner nature of living beings, which tends of itself to evolve, and the external environment surrounding them, which influences them through temperature, chemistry, and so forth. The incessant modifications of the environment cause organisms to feel the need for new functions; these, in turn, determine the appearance of new organs suited to satisfying them, while those already existing, if they continue to be useful, develop through use, and if instead they become useless, atrophy through disuse until they disappear. In this way variations are produced in organisms, appearing first in the soma but capable also of modifying the germ cells, thereby making those acquired characters hereditary. Their accumulation in successive generations will give rise to organisms so different as to form new species. That inner necessity to evolve will then cause these modifications always to advance organisms upward on the scale of living beings.
2. Neolamarckism. — This name ought to include all those authors who, while accepting Lamarck’s theory, have overestimated the action of one factor in relation to the other. Historically, however, neolamarckists are those who assign prevailing importance to environmental factors, such as Spencer, Eimer, Cope, etc.; whereas Nägeli, Rosa, etc., who make evolution depend predominantly or even entirely on internal factors, are commonly called proponents of the theory of “internal causes.”
3. Darwinism (1859). — In a population of individuals, no two are ever found to be perfectly alike. According to Darwin, the differences are due to the always somewhat different conditions in which the germs develop. Nor is it the case that such differences are advantageous in every instance; indeed, generally they are either indifferent or even harmful. But just as in breeding the human being selects individuals bearing a particular character that he wishes to perpetuate and, through suitable measures, makes it stable, creating new breeds and varieties of animals and plants, so in nature it selects individuals bearing characters advantageous for the environment in which they live, while inexorably eliminating the others. In fact, in the struggle for life, the weak and the inept perish, and only the strongest survive to sexual maturity. Consequently, advantageous characters are transmitted to the offspring and accumulate through the succession of generations, leading to the formation of organisms so different from their progenitors that they must be classified as a new species. The evolutionary process then proceeds constantly toward a higher organization, because this ordinarily represents an advantage in the struggle for life.
4. Neodarwinism. — A. Weismann, who was the first to maintain a clear separation in organisms between soma and germ, denied Darwin’s assertion that the environment could in any way influence the germ. For him, the chromosomes (v.) of germinal cells contain particles which he calls determinants, because each of them would cause the structure of a portion of the organism. The adult would therefore be predetermined in its characteristics by the collection of determinants present in the nucleus of the germ; no characteristic could develop if its corresponding determinant were absent. But since germinal cells multiply by division, the determinants too must multiply in the same way. Thus there arises a whole series of these newly formed elements, needing to assimilate and grow in preparation for a new division. At this point vital competition comes into play, whereby the more robust determinants, or those that accidentally find themselves in more advantageous positions, can grow to a greater extent at the expense of the weak and of those not favored by chance. Consequently, the characteristics dependent on them will also become more highly developed, and the organisms will find themselves privileged in the other vital competition, maintained by Darwin, between individual and individual. Since only these better-endowed organisms will reach sexual maturity, they alone will transmit their robust determinants to their offspring, and these will continue to improve in successive generations until they produce new species.
5. Mutationism (1901). — Whereas Lamarck and Darwin placed at the basis of e. the slow accumulation over time of slight individual differences, De Vries maintained instead that e. is due to the emergence of considerable variations which appear suddenly and are caused in one or more individuals of the same species, producing in them entirely new and hereditary characteristics (mutations). These characteristics are sometimes so significant as to establish a new species by themselves; more often it will be necessary to await the appearance of further variations in the same way in the same individuals before they can be separated from the parent species. Precisely because they are accidental, not all these variations are advantageous to the organisms that bear them; but the intervention of vital competition and natural selection will preserve the favorable ones while eliminating the harmful ones. According to De Vries, the profound cause of such mutations is to be sought in the influence that an unusual environment exerts upon organisms, reaching as far as their germ; but there the variation would remain latent (premutation) for several thousand years, only to erupt one day suddenly, without any apparent cause.
6. Neomutationism. — 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 maintain—as experience in fact confirms—that alteration of the germ manifests itself immediately in the offspring derived from II.
7. Hologonism (formulated by D. Rosa in 1909 and later more fully developed in 1918). — It returns to the first Lamarckian evolutionary factor, to which exclusive importance is attributed. Just as the development of the individual, from the egg to the adult state, is caused and directed solely by internal factors, while the influence of the environment is limited to permitting or preventing it from taking place, so the e. of species is due to factors intrinsic to organisms, and the environment is asked only to offer the general conditions that do not prevent life. Thus, not only do species evolve while the environment remains unchanged, but variations in it have no bearing on the direction assumed by e., except by producing phenotypic characteristics that are not transmissible to offspring. Moreover, just as the adult organism derives from a single egg cell which divides into two daughter cells, which in turn divide into two others, and so on, gradually producing cells increasingly differentiated and different from the original egg cell, so from a single ancestral living being the other, gradually more differentiated species were formed by dichotomous division. In the dichotomous division of species, however, one branch is precocious and the other late-developing; the former reaches its apogee sooner but produces a smaller number of species and retains a simpler structure (persistence of the lower forms); the latter, in its slower development, attains a more complex organization and gives rise to a greater number of further ramifications.
This theory is still upheld by several Italian biologists, whereas abroad it is shared by very few scientists. Among the other theories, at least the following deserve mention: Smuts’s holism; Lloyd Morgan’s emergent e.; and Bergson’s creative e.
III. EXAMINATION OF THE THEORIES
It is perhaps appropriate to indicate briefly the principal objections that were raised against the theories mentioned.1. Lamarckism. — That the environment can induce modifications in an organism is an incontestable fact, just as it is certain that the use and non-use of an organ causes it to tend toward greater development or, on the contrary, determines its atrophy. But are these acquired characteristics of the parents transmissible to the offspring? a) It is already unclear how they could be. In fact, germ cells are part of the organism like any other cell of the body; now, the greater or lesser development of a muscle, for example, has no effect whatsoever on the visual cells of the eye; why, then, should it affect the germ cells? Perhaps through special substances produced by the altered organs and reaching the germ by way of the blood or humors? But these hypothetical substances would have to be so specific to each organ and each part of an organ as to justify the alleged reproduction in the offspring of those same structures acquired by the parents; which, even in theory, seems at the very least excessive. b) Moreover, all the experiments conducted for decades, with every means at our disposal, to demonstrate the heredity of acquired characteristics have either produced openly negative results (the overwhelming majority) or yielded results so uncertain that for the moment they do not permit an affirmative conclusion.
2. Darwinism. — Darwinism starts from those slight differences observable among even the most similar individuals, called fluctuations by modern geneticists, and maintains that natural selection acts upon them, preserving the organisms best suited to the place and time in which they live, and thus leading to a progressive accumulation of those small diversities. Now, this is an unsubstantiated claim, if indeed it does not contradict the scientific data in our possession. a) First of all, the effects of artificial and natural selection cannot be equated, since natural selection lacks the intelligence and the means that enable human beings to isolate and cross with one another individuals bearing a particular characteristic. b) Natural and artificial selection, moreover, do not in reality produce anything new, but merely preserve and bring to appearance what already exists; they are therefore insufficient to explain the emergence of new forms. c) Furthermore, fluctuating characteristics are not transmitted to the offspring, which instead inherits only the variability proper to the species; indeed, nature tends preferably to preserve individuals that depart least from the average type—precisely the opposite of what Darwin asserts. d) Finally, it is impossible to understand what real advantage the few organisms endowed with a very slight favorable characteristic could have had in the struggle for life, in comparison with the numerous others that lacked it and with the formidable destructive forces of the environment and of natural enemies. All the more so because the presumed advantage would have been limited to adult organisms in which that favorable characteristic had developed; consequently, all the young (in which it was practically absent) would have had to perish in the struggle for life.
3. Mutationism
Does mutationism succeed in explaining evolution? It does not seem so. a) Non-lethal mutational variations concern minor characteristics which, although they may account for the formation of races, varieties, or even systematic species, are entirely insufficient to constitute the major groups; that is, they produce a microevolution admitted even by fixists, not macroevolution. b) Nor is it clear how they could determine the latter. As far as we know, mutations occurring in nature are relatively very rare. Now, from these one must subtract 80–90 percent, which cannot be regarded as a factor in evolution, since they prove regressive with regard to the vitality of organisms, giving rise to individuals of low vigor or even pathological individuals, incapable of withstanding the struggle for life. Of the few that remain, one must still disregard the indifferent ones and concentrate on the very few advantageous ones. But even the latter are generally recessive and must therefore be present in both parents in order to manifest themselves in the offspring. Yet what probability does one of these mutated organisms, lost among an entire population of normal individuals, have of mating with another organism carrying the same mutation? And how, then, can the ever-increasing evolution be explained if mutations are random, and the simultaneous—or nearly simultaneous—outburst of numerous new forms very well adapted to their environment, as paleontology documents for us, if mutations are rare, regressive, and recessive?4. Otogenism
It is undoubtedly a very ingenious theory; but, from the speculative point of view, it is difficult to understand why the germinal plasma should always and only divide dichotomously (the comparison of the evolution of species with the ontogeny of the individual must be regarded as purely metaphorical); and, from the standpoint of the facts, paleontology does not confirm, except in certain cases, the dichotomous succession of animal and plant forms.Nevertheless, these and the other theories already devised, as well as those that may be formulated in the future, may be partly or entirely false without necessarily prejudicing the doctrine of evolution, whose existence must be discussed on the basis not of theories but of the facts available. These are now numerous and constitute the evidence for evolution. We shall mention the principal ones.
IV. PROOFS
Organisms, as comparative anatomy and physiology teach us, are generally formed of cells, whose number varies from one (protozoa and protophytes) to exceedingly high figures (metazoa and metaphytes). The form of these cells may differ, but this creates no difficulty for e., since even the cells of a single higher organism are different, although they all derive from a single egg cell. Amid such diversity of form, however, every cell is fundamentally identical both in structure (all are composed of cytoplasm and a nucleus), in chemical composition (protein substances), andin functioning (all take in nourishment by intussusception, grow, multiply, age, and die).
Striking similarities are also found at levels higher than the cellular. Comparing, for example, the skeletons of vertebrates, one finds the same bones, the same mutual relationships, the same mode of formation, and so forth. 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, at least proximate, and at once scientific and satisfactory explanation?
All the more so because embryology confronts us with other facts that are, and appear to be, rather reluctant to be explained by the fixist hypothesis. To mention a few: E. Haeckel, borrowing the idea from other authors but specifying it more precisely through his fundamental biogenetic law, pointed out that higher organisms rapidly pass through, in ontogenetic development, those same stages that were the stages in the e. of their species; hence today ontogeny is the recapitulation of phylogeny. As a particular case, one may recall the branchial arches of vertebrates. It is known that adult fish breathe through gills, arranged laterally immediately behind the head: water enters through the mouth and exits through the branchial clefts, where the oxygen dissolved in it is extracted for respiration. The rudiments of the branchial clefts appear fairly early in the embryo, but the functional gills are formed only after numerous processes of differentiation. Now, in the embryos of reptiles, birds, and mammals (which, in the adult state, breathe through lungs), the rudiments of the branchial arches appear. The branchial stage is therefore transitory in them, whereas it is definitive in fish, as Haeckel’s law requires.
All present-day birds lack teeth; nevertheless, during the embryonic development of some, dental rudiments appear and subsequently regress. In the evolutionary interpretation, this fact is well explained by recalling that the first birds (archaeopteryx) had very powerful teeth, as paleontology testifies.
To limit ourselves to one final fact from embryology, we may recall that the adult slow-worm lacks limbs, whereas their rudiments are present during ontogenetic development. For the present, there seems to be no better interpretation than to link the slow-worm genetically with the ancient reptiles, all of which possessed limbs.
Further proofs are supplied by systematics. Since living beings are so similar in the fundamental element (cells) of which they are formed, and since they progress so gradually toward ever greater differentiation during embryonic development, it is not surprising (but is a new proof of the evolutionary doctrine) that adult living beings should be classifiable by the systematist in an ordered scale extending without interruption from the protozoan to man through a whole series of intermediate organisms. If living beings have derived from one another, this fact is not only explained but imposed as an absolute necessity.
The examination of present-day and fossil living beings gives us another proof through rudimentary organs—that is, organs that are still present in individuals but in rudimentary or involuted form, whereas they are well developed and functional in other organisms that are systematically lower or chronologically older, thereby proving, or at least suggesting, the genetic derivation of the former from the latter. The eyes of the mole, the bones of the hind limbs of cetaceans, the splint bones of the horse, and many others are cited.
Certainly, in order to draw an argument in favor of transformism from systematics, it must also be demonstrated that living beings appeared on earth in the order in which they are placed by the classifier; otherwise, the scalar arrangement of organisms could not be explained evolutionarily. Now, this is precisely what the study of fossils tells us. Paleontology in fact teaches, with a certainty that is now virtually absolute, that types, classes, and often orders did not appear at the same time but one after another, in the order of progressive anatomical-functional differentiation required by the theory; thus the present scalar arrangement of living beings revealed to us by systematics corresponds, on average, to their actual appearance in time. Not only that, but whereas today types and classes... are clearly separated, making it difficult to connect them genetically with one another, paleontology indicates fossil forms that constitute the transitional bridge between lower and higher forms, such as, for example, archacopteryx, the connecting link between birds and reptiles.
Furthermore, in some well-established cases, paleontology presents all or nearly all the stages of transformation through which an organism passed during the geological periods before reaching its present form (orthogenetic series). One example among all may suffice: the series of equids, in which, from the beginning of the Eocene to the Pliocene, one observes a progressive increase in size, from that of a hare in eohippus to that of our horses, as well as a progressive reduction in the number of digits. The Eocene eohippus still has four digits on the forefeet and a splint (corresponding to the fifth digit); on the hind feet it has three digits and two splints (corresponding to the first and fifth digits). The Oligocene mesohippus has three digits on the forefeet and one splint (corresponding to the first, while the rudiment of the fifth has already disappeared), and three digits without splints on the hind feet. The Pliocene neohippus has barely three digits on each foot, and of these only the middle one, having become very robust, reaches the ground; the others (the second and fourth) regress until they are reduced to the splints of present-day horses. Is this not good proof in favor of e.?
Other analogous arguments could still be drawn from paleontology itself, from biogeography, and from genetics; but they would merely be further confirmations that add nothing directly to the fundamental presentation of the proofs of transformism. It will not, however, be useless to examine briefly and summarily the extent to which the facts adduced demonstrate this doctrine.
V. CRITICA
Although many authors attribute to the arguments cited above the value of genuine proofs, to the extent that they consider e. by now demonstrated, others, perhaps fewer in number but certainly more objective, prefer to regard them rather as mere indications, and moreover expressly declare that these too must be considered as a whole and not one by one in order to derive from them any satisfactory proof. This is, given the present state of our knowledge, the safest position, since in reality the individual arguments either do not withstand calm criticism, or are evolutionist interpretations of facts that are in themselves indifferent, or, at most, support a transformation of organisms far more limited than the one that is meant to be proved; and taken together they demonstrate only that e. may have occurred.Here, in fact, is the logical procedure of convinced evolutionists: if e. existed, they argue, organisms must display the following characteristics: they must all fundamentally possess the same anatomical and physiological structure; in the course of development, the higher forms must temporarily pass through stages that are definitive in the lower forms; they must be capable of being classified by the systematist in a progressive ascending scale; the various forms must appear on earth one after another and, in particular, the higher forms after the lower. Now comparative anatomy and physiology, embryology, systematics, and paleontology respectively demonstrate all this. Therefore c. has occurred, and the fact of e. is certain.
But, in sound logic, the conclusion seems illegitimate. While it is correct to assert that, if e. existed, those facts must occur (otherwise we would have evidence to the contrary!), from the existence of those facts one may conclude only that e. may have occurred; the existence of those facts and indications is the indispensable condition for the doctrine of e. 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 evolutionist reasoning, let us examine some of the facts that form the premises of the syllogism referred to above.
With regard to the arguments supplied by comparative anatomy and physiology, one may reply that chemical bodies too fundamentally possess the same structure (atomic and subatomic) and the same modes of action (the laws of chemical reactions); yet no one can confidently maintain that they derived through successive transformations from a simpler primordial common element. Therefore this argument in itself certainly does not have the value of proof; indeed, in the hands of a fixist it could serve to confirm his thesis, since the only reasonable explanation of the similarity among inorganic bodies is reduced to this: that they are as they are because God made them so—the very same reason advanced by fixists to explain the similarity of living organisms. Nor do the facts supplied by embryology have any greater probative value. The fundamental biogenetic law, as proposed by Haeckel, has already been rejected by many of the evolutionists themselves, since comparative study does not demonstrate the resemblance of higher embryos to adult lower 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 decreases as development proceeds. Now, this may be attributed not to e. but to the same mechanical necessity of formation by which Michelangelo’s Moses and Pietà (so different when completed) had to resemble each other all the more closely the nearer they were to the stage of an amorphous marble block.
The alleged presence of gill arches in the embryos of higher vertebrates is at least partly gratuitous and the product, in interpretation, of an evolutionist mentality. In fact, these are not gill arches but simple visceral arches, which are neither gills nor ever show any sign of becoming such, since they are always destined for an entirely different function from respiration. It is true that morphologically they recall the corresponding arches from which gills will develop in fish; but it is equally true that they differ from them in many characteristics, and that the morphological resemblance can be explained by considering that fish, amphibians, reptiles, birds, and mammals, since they all belong to the animal kingdom, to the subkingdom of the menatoi, and to the vertebrate phylum, and differ from one another only in class, must necessarily have certain characteristics in common both in the adult state and in the embryonic state, independently of any fixist or evolutionist interpretation.
The same dental buds found even today in the embryos of certain birds are not convincing proof, for two reasons: first, histological study does not reveal the presence of buds but, at most, of dental ridges, which are an early formation from which the true buds should subsequently be constructed, with the participation of other cellular layers; in our case, however, they never form at all (indeed, Rose and Carlsson question whether they are dental ridges); second, if those ridges really are an atavistic memory, they raise the question of why they do not appear in the embryos of all birds. Nor is it valid to reply that some have evolved more and others less, since what is at issue here is proving, not assuming, the very existence of e.
Finally, the case (and analogous cases) of the embryo of the slow-worm, in which the buds of limbs appear and then regress so extensively that the adult is apodal, may more appropriately be cited as an example of regression, certainly not as a sign of progressive e.
Systematics and paleontology remain. But here too, although it is entirely true that in our museums living beings are classified in an ascending order, this fact does not constitute proof of genetic derivation, since chemical bodies too can be arranged in a graduated scale, as Mendelejeff did with such precision that he predicted the existence of elements still unknown at the time; yet nothing authorizes us to regard them as historically derived from one another in that definite order. In living beings, moreover, gradation disappears precisely where it would be most necessary to demonstrate e.: namely, in the passage from phylum to phylum, from class to class... at which levels there always exists a profound biological gap that neither systematics nor paleontology has managed to bridge. The appearance of phyla, classes, and often even orders is always abrupt; and the fact that it has not yet been possible to demonstrate the existence of a single genuine connecting link is truly perplexing. Archaeopteryx, for example, which is always cited as a bridge of transition from reptiles to birds because it has the general structure of the latter and the long vertebral tail and tooth-bearing jaws of the former, does not withstand criticism, since neither the vertebral tail nor teeth are characteristics of reptiles. Turtles belong to the class of reptiles, and yet they lack teeth, as did those of the Jurassic period contemporary with Archaeopteryx; pterodactyls are reptiles found in the same Jurassic lithographic limestones of Bavaria where Archaeopteryx was discovered, and yet they had a very short or even entirely absent tail.
And two further facts add to the perplexity: the not exceedingly rare reversals of the order that would be required by the transformist doctrine, and above all the simultaneous, rather than successive, presence of many types. In the oldest known fossil-bearing strata (the Precambrian), alongside unicellular beings there are already annelids, mollusks, echinoderms...
Certainly, their contemporaneity could be only apparent, in the sense that those strata, on the one hand, are almost entirely unknown to us and, on the other, lasted for millions of years, so that it is difficult to speak of contemporaneity, since the types may have appeared one after another during that very long period. This is a legitimate supposition; but it is clear that, by multiplying marginal hypotheses, one renders the structure of evolution unstable. The orthogenetic series, moreover (equids, cetaceans...), are so limited that they do not justify extending the argument to classes and, still less, to phyla; not to mention that they do not demonstrate a progressive ascent of organisms on the scale of living beings, but only a restricted variability on their part.
In conclusion, it may be said that the doctrine of evolution is to this day a good scientific theory and a useful working hypothesis, but that it is undoubtedly excessive to regard it as a truth now demonstrated.
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