Evolution

EVOLUTION. - Evolutionism (transformism, phylogeny, descent theory) is the scientific doctrine that affirms the natural derivation of higher organisms from lower ones. Since paleontology teaches that living beings appeared on earth one after another, and, on average, the more differentiated after those structurally simpler, two hypotheses are possible: that each natural species of organisms had in time an autonomous and independent origin (fixism); or that the higher species derived from the lower ones (evolutionism).

I. GENERAL NOTIONS

The doctrine of evolution was and is upheld by all materialists and by several even of the spiritualists, but naturally with different postulates. For materialists, not only are higher living beings derived from lower ones through physico-chemical causes, but these in turn from others still simpler, formed spontaneously from inorganic matter, which, in its turn, is eternal and uncreated; even the human soul would derive by transformation from the soul of the brutes. For theists, matter is the effect of a creative act of God; the first living beings, according to some, would have originated by spontaneous generation, according to others they too would have been created by God in one (monophyletism) or more specimens (polyphyletism) from which all the species appearing subsequently in the geological periods would then have taken origin. For theists, the soul of man is created directly by God; the body derives instead from the body of an anthropoid.

Evolutionism as upheld by materialists is unacceptable because it conflicts with certain scientific data (for the philosophical errors of materialism, v. MATERIALISM). That matter is eternal is against the second law of thermodynamics, inasmuch as, if this were so, absolute disorder and complete immobility ought to reign today in the universe, all the asymmetries that make energy usable having already had to disappear. If therefore matter began to exist in time, it is created. That the first organisms were formed by spontaneous generation (let us too use this expression, however inexact) is contradicted by the experiments of Redi, Vallisneri, Spallanzani and above all of Pasteur as regards known organisms; if moreover it were maintained that the first living beings possessed a structure much more elementary than the most elementary organisms known to us today, so that their direct formation from matter was possible, the assertion is gratuitous in its first part and, in its second, clashes with the laws of probability, since, however simple one may wish to suppose them, those primitive organisms must always have possessed a heterogeneity and asymmetry such (with respect to inorganic matter) as to constitute an event supremely improbable on theoretical grounds, and practically impossible to occur in nature. That moreover the evolution of the lower forms was governed only by physico-chemical forces is against the sure data of paleontology, which demonstrates that, on average, there was a continuous progression of living forms, with the production of organisms always suited to their environment; whereas, if it were true that evolution was governed only by chance, alongside a few well-succeeded forms one ought to find very many unsuccessful ones. That finally the human soul represents merely a further perfecting of that of the brutes is contradicted, at least indirectly, by experimental psychology.

Theistic evolutionism instead (except, for the reasons stated above, the group that admits spontaneous generation) is a good scientific doctrine. As regards the extension of the transformist theory to the origin of man, v. EVOLUZIONISMO.

II. THEORIES

It is necessary, from the outset, to keep carefully distinct the fact of evolution from the manner in which it occurred or may have occurred. The modalities and the 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 down with them into ruin the fact of evolution, which 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 in these hundred years, at least those most classic are briefly recalled.

1. Lamarckism

Lamarck (1809) assigns two essential causes that would have produced the evolution of organisms: the intimate nature of living beings, which tends of itself to evolve, and the external environment that surrounds them and influences them by means of temperature, chemistry, etc. The incessant modifications of the environment bring it about that organisms feel the need for new functions, which in their turn determine the appearance of new organs suited to satisfying them, while those already existing, if they still serve, continue through use to develop, but if they become useless, through disuse they atrophy until they disappear. In this way variations are produced in organisms, manifesting first in the soma, but capable also of modifying the germinal cells, thus rendering those acquired characters hereditary. Their accumulation in successive generations will give rise to organisms so different as to form new species. That intimate necessity of evolving will then bring it about that these modifications always make organisms progress on the scale of living beings.

2. Neolamarckism

Under this name should be included all those authors who, while accepting Lamarck's theory, have overvalued the action of one of the factors relative to the other. Historically, however, neolamarckists are those who attribute a 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 upholders of the theory of "internal causes."

3. Darwinism (1859)

In a population of individuals, no two are ever encountered perfectly alike. The differences are due, according to Darwin, to the always somewhat different conditions in which the germs develop. And it is not said that such differences are in every case advantageous; on the contrary, in general they are either indifferent or even harmful. But, just as in breeding the human being selects the individuals carrying a particular character that he wishes to perpetuate, and, with suitable contrivances, renders it stable, creating new races and varieties of animals and plants, so in nature he selects the individuals carrying characters advantageous for the environment in which they live, in order to inexorably suppress the others. Indeed, in the struggle for existence, the weak and the unfit succumb and only the strongest survive to sexual maturity. Consequently, the advantageous characters are transmitted to the offspring and accumulate in the succession of generations, leading to the formation of organisms so different from their ancestors as to have to be classified in a new species. The evolutionary process then unfolds constantly toward a higher organization because this, as a rule, represents an advantage in the struggle for existence.

4. Neo-Darwinism

A. Weismann, who was the first to maintain 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, in the chromosomes (v.) of the germ cells there are contained particles that 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 characters by the collection of determinants present in the nucleus of the germ, and no character could develop if the corresponding determinant were missing. But since the germ cells multiply by division, the determinants must likewise multiply in the same way. And so there then arises a whole series of these newly formed elements, under the necessity of assimilating and growing in order to prepare 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 more at the expense of the weak and of those not favored by chance. Consequently, the characters that depend on them will also turn out to be more developed, and the organisms will find themselves privileged in that other vital competition, upheld by Darwin, between individual and individual. Since only these better-endowed organisms will reach sexual maturity, they alone will transmit to their offspring their robust determinants, which 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 arising of notable variations that appear suddenly and by chance in one or more individuals of the same species, determining in them totally new and hereditary characters (mutations). Such characters are sometimes so significant as to establish, by themselves, a new species; more often it will be necessary to wait until other variations arise in the same way in the same individuals before they can be split off from the parent species. Precisely because they are random, not all these variations are advantageous for the organisms that bear them; but the intervention of vital competition and of natural selection will preserve the favorable ones by eliminating the harmful ones. The profound cause of such mutations must be sought, for De Vries, in the influence that an unusual environment exerts on organisms, to the point of reaching their germ; but here the variation would remain latent (premutation) for some thousands of years, only to explode one day suddenly 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, and maintain instead (as experience, moreover, confirms) that the alteration of the germ manifests itself immediately in the offspring derived from it.

7. Hologenism (enunciated by D. Rosa in 1909 and then better developed in 1918)

It links back to the first Lamarckian evolutionary factor, to which an 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 occurring, 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. Therefore, not only do species evolve even while the environment remains unchanged, but changes in the latter do not affect the orientation that e. comes to assume, except by producing phenotypic characters that cannot be transmitted to the offspring. Moreover, just as the adult organism derives from a single egg cell that divides into two daughter cells which in turn divide into another two, and so on, producing little by little cells ever more 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. However, in the dichotomous division of species, one branch is early and the other late; the first reaches its apogee sooner but generates a smaller number of species and preserves a simpler structure (persistence of lower forms); the second, in its slower development, reaches 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 to be remembered: the holism of Smuts; the emergent e. of Lloyd Morgan; and the creative e. of Bergson.

III. EXAMINATION OF THE THEORIES

It is perhaps appropriate to indicate briefly the principal objections that have been raised against the theories recounted.

1. Lamarckism

That the environment can induce modifications in an organism is an incontestable fact, just as it is certain that the use and disuse of an organ makes it tend toward greater development or else determines its atrophy. But are these characters acquired by the parents transmissible to the offspring? a) For one thing, it is not clear how they could be. In fact, the 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 whatever on the visual cells of the eye; why then should it influence 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 for each organ and particle of an organ as to justify the asserted reproduction in the offspring of those very structures acquired by the parents; which, even on theoretical grounds, seems at the very least excessive. b) Moreover, all the experiments conducted for decades and by every means at our disposal to demonstrate the heredity of acquired characters have either given openly negative results (the vast majority), or have had outcomes so uncertain as not to permit, for now, an affirmative conclusion.

2. Darwinism

Darwinism starts from those slight differences found among even the most similar individuals, called fluctuations by modern geneticists, and maintains that natural selection operates upon these, 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 gratuitous, even when it does not contradict the scientific data in our possession. a) First of all, the effects of artificial and of natural selection cannot be equated, since the latter lacks the intelligence and the means that allow man to isolate and cross with one another the individuals carrying a particular character. b) Natural and artificial selection, moreover, in reality produce nothing new, limiting themselves to preserving and bringing out what already exists; they are therefore an insufficient element for explaining the appearance of new forms. c) Furthermore, fluctuating characters are not transmitted to the offspring, which instead inherits only the variability proper to the species; indeed nature tends to preserve by preference the individuals that deviate least from the average type; that is, the opposite of what is affirmed by Darwin. d) Finally, it is not understood what real advantage the few organisms endowed with a very slight favorable character could have had in the struggle for life, in the face of the numerous others that were devoid of it and in the face of the formidable destructive forces of the environment and of natural enemies. All the more so since the presumed advantage had to be limited to adult organisms in which that favorable character was developed; so that 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 small characters which, while they can account for the formation of races, varieties, or even systematic species, are wholly 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, the mutations that occur in nature are relatively very rare. Now, from these one must subtract 80-90%, which cannot be regarded as a factor of evolution since they prove regressive in relation to the vitality of organisms, giving rise to individuals that are scarcely thriving or even pathological, incapable of sustaining the struggle for life. Of the few that remain, one must further disregard the indifferent ones, in order to stop at the very few advantageous ones. But even these latter are generally recessive, and must therefore be present in both parents in order to manifest themselves in the offspring. But what probability has one of these mutated organisms, lost in the midst of an entire population of normal individuals, of crossing with another organism carrying its own same mutation? And how then to explain the ever-increasing evolution if mutations are random, and the simultaneous, or nearly simultaneous, explosion of numerous new forms very well adapted to their environment, as paleontology documents for us, if mutations are rare, regressive and recessive?

4. Orthogenesis

It is an undeniably very ingenious theory; but, from the speculative point of view, it is not clear why the germ plasm must 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 point of view of the facts, paleontology does not confirm, except in a few cases, the dichotomous succession of animal and plant forms.

Nevertheless, these and the other theories already devised and those that may be formulated in the future can be in part or wholly false without necessarily prejudicing the doctrine of evolution, the existence of which must be discussed on the basis not of theories but of the facts available. These are by now numerous and constitute the proofs of evolution. The principal ones will be touched upon.

IV. EVIDENCE

Organisms, as comparative anatomy and physiology teach, are generally formed of cells, whose number varies from one (protozoa and protophytes) to very high figures (metazoa and metaphytes). The form of these cells can be different, but this does not create a difficulty for evolution, since even the cells of one and the same higher organism are different, although all deriving from a single egg-cell. In such diversity of form, however, both the structure (all are constituted of cytoplasm and of a nucleus), and the chemical composition (protein substances), and the functioning (all nourish themselves by intussusception, grow, multiply, age and die) are fundamentally the same for every cell.

Surprising similarities are also found at levels higher than the cellular one. Comparing, for example, the skeletons of vertebrates with one another, one finds the same bones, the same reciprocal relations, the same mode of formation, etc. Now then, in the evolutionist doctrine which derives all living beings from one or a few ancestral forms, do these undeniable resemblances not find a natural, at least proximate, explanation that is at once scientific and satisfactory?

All the more so since embryology confronts us with other facts that are, and seem, rather reluctant to let themselves be explained by the fixist hypothesis. To cite a few: E. Haeckel, borrowing it from other authors but specifying it better with his fundamental biogenetic law, has pointed out that higher organisms traverse at a rapid pace, in ontogenetic development, those very stages that were the steps of the evolution of their species; so that today ontogeny is the recapitulation of phylogeny. As a particular case, the branchial arches of vertebrates are recalled. It is known that adult fish breathe by gills, arranged laterally just behind their head: water enters through the mouth and exits through the branchial clefts, where the dissolved oxygen is removed from it for respiration. The rudiments of the branchial clefts appear fairly early in the embryo, but only after numerous differentiating processes are the gills formed that are capable of functioning. Well then, in the embryos of reptiles, birds, mammals (which in the adult state breathe by 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.

Present-day birds are all devoid of teeth; and yet in the embryonic development of some, dental rudiments appear which then regress. In the evolutionist interpretation the fact is well explained by recalling that the first birds (archaeopteryx) had very powerful teeth, as paleontology testifies.

To limit ourselves to one last fact from embryology, we can recall that the adult slowworm is devoid of limbs, whereas their rudiments are present during ontogenetic development. There does not seem to be for now any better interpretation than to link the slowworm genetically to the ancient reptiles, all provided with limbs.

Other proofs are furnished to us by systematics. Thus similar in the fundamental element (cells) of which they are formed, and thus gradually progressive in assuming an ever greater differentiation during embryonic development, it is then no wonder (but it is a new proof for the evolutionist doctrine) if adult living beings must be classifiable by the systematist in an ordered scale that continues uninterrupted from the protozoon to man through a whole series of intermediate organisms. If living beings are 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, that is, with organs that are present even today in individuals but in rudimentary or involuted form, whereas they are well developed and functioning in other organisms that are systematically lower or chronologically more ancient, proving or at least suggesting a genetic derivation of the former from the latter. There are cited: the eyes of the mole, the bones of the posterior limbs of cetaceans, the splint bones of the horse, and many others.

Certainly, in order that an argument in favor of transformism may be drawn from systematics, it will still be necessary to demonstrate that living beings appeared on earth in that order in which they are placed by the classifier; otherwise the scalar arrangement of organisms could not be explained evolutionistically. Well then, precisely this is what the study of fossils tells us. Paleontology in fact teaches, with a certainty that is by now absolute, that the types, the classes and often also the orders appeared not at the same time, but one after the other, in the order of progressive anatomical-functional differentiation required by the theory; so that 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 if today the types, the classes... are sharply separated in such a way that it is difficult to link them genetically to one another, paleontology indicates fossil forms that constitute the bridge of passage between the lower and the higher, such as, for example, the archaeopteryx, the connecting link of birds with reptiles.

And further, in some well-ascertained case, paleontology presents all or nearly all the terms of transformation through which an organism passed in the geological periods before reaching its present form (orthogenetic series). Let the series of equids serve, for example, for all of them, in which one witnesses, from the beginning of the Eocene to the Pliocene, a progressive increase in size going from the size of a hare of eohippus to that of our horses; and a progressive reduction of the digits. The Eocene eohippus still has 4 digits on the forelimbs and a splint (corresponding to the 5th digit); 3 digits and 2 splints (corresponding to the 1st and 5th digits) on the hindlimbs. The Oligocene mesohippus has 3 digits on the forelimbs and a splint (corresponding to the 1st, while the rudiment of the 5th has already disappeared), and 3 digits without splints on the hindlimbs. The Pliocene neohippus has barely 3 digits per limb and of these only the middle one, having become very robust, reaches the ground; the others (the 2nd and the 4th) regress until they are reduced to the splints of present-day horses. Is this not a good proof in favor of evolution?

Other analogous 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 framing of the proofs of transformism. It will not, however, be useless to examine briefly and summarily to what point the facts adduced demonstrate this doctrine.

V. CRITICISM

Although many authors attribute to the arguments cited above the value of authentic proofs, so much so that they consider e. as by now demonstrated, others, perhaps fewer in number but certainly more objective, prefer to regard them rather as simple indications, and moreover expressly declare that even these must be considered as a whole and not one by one in order to derive from them some satisfactory proof. This is, in the present state of our knowledge, the safest position, since, in reality, the individual arguments either do not withstand serene criticism, or are evolutionistic interpretations of facts indifferent in themselves, or, at most, argue for a transformation of organisms far more restricted than that which is intended to be proved; and their ensemble demonstrates only that e. may have occurred.

Here indeed is the logical procedure of convinced evolutionists: if e. existed, they argue, organisms must present the following characteristics: all fundamentally to possess the same anatomical-physiological structure; in development, the higher to pass temporarily through stages that are definitive in the lower; to be able to be classified by the systematist in a progressive ascending scale; the one to appear on earth after the other and, in particular, the higher after the lower. Now, comparative anatomy and physiology, embryology, systematics and paleontology demonstrate respectively all this. Therefore e. has occurred and the fact of e. is certain.

But, in good logic, the conclusion seems illegitimate. While it is correct to affirm that, if e. existed, those facts must occur (otherwise we would have the proofs of the contrary!), from the existence of those facts one must 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 evolutionistic reasoning, let us come to the examination of some facts that form the premises of the syllogism referred to above.

Regarding the arguments furnished by comparative anatomy and physiology, one can reply that chemical bodies too have fundamentally the same structure (atomic and subatomic) and the same modalities of action (laws of chemical reactions); and yet no one can with certainty maintain that they derived through successive transformations from a common primordial simpler element. Therefore this argument in itself certainly does not have the value of a proof; indeed it could serve in the hands of the fixist to confirm himself in his thesis, since the only reasonable explanation of the similarity among inorganic bodies reduces to this: that they are such because God made them such: the same reason, that is, brought 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 of the 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 proves all the greater the more precocious the embryonic stage considered, so that it diminishes as development proceeds. Now, this can be attributed not to e. but to the same mechanical necessity of formation by which the Moses and the Pietà of Michelangelo (so different once completed) had to resemble each other all the more the closer they were to the stage of formless marble block.

The asserted presence of branchial arches in the embryos of higher vertebrates is at least in part gratuitous and the fruit, in interpretation, of the evolutionistic mentality. In fact it is not a question of branchial arches but of simple visceral arches that are not gills nor ever show signs of becoming such, being always destined for an entirely different function than the respiratory one. It is true that morphologically they recall the corresponding arches from which in fish the gills will be formed; but it is equally true that they differ in many characteristics and that the morphological similarity can be explained by thinking that fish, amphibians, reptiles, birds and mammals, since they all belong to the animal kingdom, to the subkingdom of metazoans, to the vertebrate type and differ among themselves only in class, must necessarily have characteristics in common both in the adult state and in the embryonic one, independently of any fixist or evolutionistic interpretation.

The same dental rudiments observable even today in the embryos of certain birds are not a convincing proof, for two reasons: in the first place, histological study does not reveal the presence of rudiments, but, at most, of dental ridges which are an early formation from which later, and with the participation of other cellular layers, the true rudiments should be constructed, which in our case however never form (indeed Rose and Carlsson cast doubt on whether they are dental ridges); in the second place, if those ridges are truly an atavistic recollection, they give rise to the problem of why they do not appear in the embryos of all birds. Nor is it worth replying that some have evolved more, others less, since here it is a question of proving and not of supposing the very existence of e.

The case finally (and analogous ones) of the embryo of the slowworm, in which the rudiments of the limbs appear and then regress so much that the adult is apodous, can more opportunely be cited as an example of regression, certainly not as a sign of progressive e.

There remain systematics and paleontology. But here too, although it is very true that, in our museums, living beings are classified in an ascending order, the fact does not constitute a proof of genetic derivation, since chemical bodies too can be arranged in a scalar manner as was done by Mendeleev with such precision as to predict the existence of elements at that time still unknown; and yet nothing authorizes us to hold that they derived historically one from another in that determined order. In living beings, moreover, gradualness fails precisely when it would be most required to demonstrate e.: in the passage, that is, from type to type, from class to class..., between which levels there always exists a profound biological gap that neither systematics nor paleontology has succeeded in filling. The appearance of types, of classes and often also of orders is always sudden; and the fact that it has not yet been possible to demonstrate the existence of a single true connecting link really leaves one perplexed. The archaeopteryx, for example, which is always cited as a bridge of passage from reptiles to birds, because it has the general structure of the latter and the long vertebrated tail and the jaws armed with teeth of the former, does not withstand criticism since neither the vertebrated tail nor the teeth are characteristics of reptiles. Turtles belong to the class of reptiles, and yet they are devoid of teeth as those of the Jurassic contemporary with the archaeopteryx were devoid of them; the pterodactyls are reptiles found in the same lithographic limestones of the Jurassic of Bavaria where the archaeopteryx was discovered, and yet they had a very reduced tail or even none at all.

And two other facts add to increase the perplexity: the not excessively rare inversions with respect to the order that would be required by the transformist doctrine, and above all the contemporary and not successive presence of many types. In the most ancient fossiliferous strata known (Precambrian), alongside unicellular beings are already found annelids, mollusks, echinoderms...

Of course, their contemporaneity might 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 could have appeared one after the other in that very long span of time. This is a permissible supposition; but it is clear that by multiplying marginal hypotheses one makes the edifice of evolution unstable. Moreover, the orthogenetic series (equids, cetaceans...) are so limited as not to legitimize the extension of the argument to classes and, even less, to types; not to mention that they do not demonstrate a progressive ascent of organisms on the scale of living beings, but only a restricted variability of theirs.

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 by now demonstrated.

Giuseppe Bonio