The History of Biological Theories

Bird migrations have been studied by recent workers, with these objections in mind. Our birds move towards the south, but that is only a part of a more widespread migration. In every region, from the extreme north to the Equator, birds are on the move. They stream in one direction in autumn ; in the opposite direction in spring. H. Friedmann has developed certain views about geo- graphical distribution which are absolutely opposed to the assumptions made by Darwin. 1 He goes back to the ideas of Agassiz, ridiculed by the Darwinists. The home of each species is, according to him, an important characteristic of that species, and is not to be explained by migrations, by dispersal, or by any external circumstance whatsoever. He believes in the spontaneous origin of each species, and hence that each stands in the most intimate relationship with its natural surroundings; there are psychical bonds between the milieu and the organism ! This author stands quite alone in these views.

Botanists never got as far from the ideas of Humboldt as did the zoologists. The plant world was so simply and so obviously dependent upon its surroundings. Schimper in his Physiological Geography of Plants (1898)2 indicated the 2 A. Schimper, Pflanzengeograpbie auf pbys iologiscber Grundlage, 1898. awakening of new interest in this subject by his very title. It is significant that the author calls himself a Neo- Lamarckian. Among zoologists in general the direct physiological dependence of the animal upon its surroundings has been little regarded, although undoubtedly the animal world could also be divided up into 'formations' determined by external conditions. Entomologists, however, have always studied insects in relation to their environment. They distinguish between insects which live in mud, which live underground, and so on ; further, between nocturnal and diurnal insects, between hopping, running, and creep- ing insects, &c.

The same mode of life is seen repeated in many hetero- geneous animals. This seems to suggest that the possible ways of living are not unlimited, but are determined by unalterable laws, even as bodily structure can only vary within certain limits. The habits of life of the mole are repeated by the mole-cricket (Gryllotalpa) ; those of the termites by the ants ; the gait of the kangaroo is seen again in the jerboa (Dipus), and such examples could be multiplied.

Modern work on ocean fauna, on freshwater and on cave animals, makes it apparent that there has been some .recession from the Darwinian view of distribution. There is less tendency to study one kind of animal and its rela- tion to others occupying the same or different territory. This type of work is replaced by study of the whole group of animals inhabiting any one area and of the common characteristics exhibited by the group. The most favoured field for this work is that offered by the ocean deeps and their fauna. In these depths animals live under peculiar conditions. There is here no light of sun or star, neither the blue heavens nor green plants ; here no noise penetrates, no wave moves, there is no day or night all seasons are as one. Temperature is invariable and near o C., and there is a constant pressure of over loo atmospheres.

In this realm of eternal darkness and silence live fishes, molluscs, crabs, echinoderms, but no plants. Dead diatoms and the corpses of animals sink gradually from the more superficial layers, and afford the only source of nourishment for certain of these deep sea forms, while the rest are carnivorous and live on their neighbours. Some of these animals are very ancient forms which have long ago disappeared from the shallower parts of the ocean. Among these are numerous Crustacea and quaint creatures called sea-spiders, whose precise relationships are un- certain ; the sea-hedgehog (Calveria^ which is known as a fossil also), feather-stars (crinoids) ; the degenerate sea- squirts ; Terebratula, found attached to rocks at a depth of 4,000 metres, which was living in Jurassic times.

Some of these animals especially the crabs are blind. Most of them possess large and peculiar eyes, which often project from the head like telescopes ; many have peculiar luminous bodies which give out a greenish light. Some are colourless. The deep-sea fishes, however, are usually dark grey or black. Some deep-sea crabs are crimson. Some creep over the floor of the ocean, or adhere to it. Unicellular animals (Foramenifera), beautiful sponges and polyps, showing wonderful colouration, echinoderms and crabs are among the deep-sea fauna. Some of these creatures float in the water, and never come into contact with the solid earth ; others crawl on the bottom.

Marvellous are these deep-sea animals; still more marvellous the fact that there is not one order of animals known to us from the ocean depths alone although the conditions there are so utterly different from those at the surface. The forms of organic life develop within such strictly defined limits that even such very different en- vironmental conditions have not altered more than minor details in the structure of these animals. The theories of both Lamarck and Darwin are powerless to explain these facts.

history of life passes from unknown beginnings, JL through long epochs from which only very question- able traces of organic life have come down to us, then on to the periods when fossils begin. These preserve for us what are, in a sense, printed records of that past life. We divide this history of organic life into periods ancient (palaeo- zoic), the middle ages (mesozoic), and recent (caenozoic) ; to these must be added the most recent period of all, during which man has existed, the anthropozoic. These periods are subdivided, and the subdivisions bear special technical names.

We do not know for how long each period endured, nor how old our planet is. During the eighteenth century most geologists were still influenced by the Biblical teach- ing, according to which the earth was first created 6,000 years ago. Even at that time, however, Buffon estimated that its age was much greater; he suggested 65,000 years, but was not able to fill in this long period with any definite events. It was the English geologist, Hutton, who first effectively refuted the estimate based on biblical statement. He began with the assumption that all changes in the earth's crust are the result of causes like those in action to-day, and that colossal upheavals merely represent the combined effects of a series of smaller changes. He was thus forced to assume that enormous periods of time had elapsed, during which the large mountain ranges had been thrown up, the coast-line had undergone great alterations, and alluvial deposits, often thousands of metres deep, had been formed.

Charles Lyell adopted these assumptions of Hutton. He taught that the earth had been in existence for millions of years, and that small changes had been constantly in progress throughout. Darwin and his followers accepted this view, but spoke not of millions of years but of hundreds or thousands of millions during which our planet had endured. The demonstration of the fact that life upon the earth is enormously old has been compared, not inappropriately, with the revelation of the enormous vistas of space in which float the stars.

Unfortunately we do not know even approximately what is the age of life as such upon the earth, nor what has been the duration of the separate epochs. But palaeon- tology agrees with human history in this that the earlier and doubtless more fundamental modifications have taken vastly longer than the later no less striking but probably less fundamental changes. This may be expressed by saying that the earlier periods are longer, and the periods become shorter as we get nearer to our own time.

Historians of the past study the documents which have come down to them, while palaeontologists reconstruct the history of life from the fragments in certain kinds of rock which they have reason to assume are of organic origin. From the impressions and the bones of once living forms they reconstruct the appearance of extinct animals ; while, from the sequence of the layers of the earth's crust, and from the nature of the fossils these layers contain, they deduce the surroundings in which the animals and plants of each epoch lived. They have come to realize that, in a series of consecutive epochs, the earth was inhabited by quite different plants and animals.

Just as at the very dawn of human history we meet with various races at different stages of development, so in our palaeontological studies we find that the oldest known animals are very varying and fairly advanced forms Crustacea, Brachiopods, Molluscs, and the like. Among mankind the lower races have always existed side by side with more advanced ones, and they still continue to do so. Progress does not drive the whole human race forward at once, it seizes now upon this people and now that. Some peoples have remained for untold ages at the same

level of existence. Some advance to a certain level and then cease to develop, even retrogress, ultimately to dis- appear from human history. So too in organic nature. Some forms (Algae and Brachiopods, for example) have existed ever since our earliest records of life without undergoing any marked alteration. Other forms advanced for a time and then degenerated ; many of these have disappeared completely (Trilobites), others drag on as an insignificant remnant (Clubmosses). There are others, again, which in the beginning consisted of a few types only ; from these evolved an untold wealth of varying forms, which in turn became much fewer, without, however, dis- appearing altogether. The Reptiles live on a mere shadow of their former selves, for they were the dominant forms in the Mesozoic fauna.

It is difficult to deduce any law of development from the kaleidoscopic changes in the earth's history. In this connexion Huxley pointed out a strange fact. Life has existed on the earth for millions of years, and there have been millions of different forms of life. Yet, great as is this variety, it is confined within narrow limits. He who seeks among extinct animals for forms wholly different from those existing to-day is doomed to disappointment. There is no single large subdivision of the plant or animal kingdom known only from fossil representatives ; all clearly reveal their relationship to existing forms. On the other hand, some forms, notably the Brachiopods, have existed unchanged through untold ages.

The most favourable evidence that there has been a progressive evolution of life on the earth is afforded by the history of vertebrates. No vertebrates have so far been found in the oldest strata which furnish fossils. Soon, however, fishes appear. This lowest group of vertebrates has continued to this day. It is difficult to say whether they have progressed since they appeared. The simplest fish-like forms Amphioxus and the river-lamprey are not known as fossils and are very specialized and probably degenerate, while the mudfishes (Dipnoi), which are re-

garded by some anatomists as the highest group of fishes, are found as fossils in the Devonian that is, they existed in the middle of the Palaeozoic period. The next highest group the Amphibians appeared later than the fishes, in the Carboniferous, which followed the Devonian. In the next epoch, the Permian, the first reptiles appear. In the Jurassic come the first birds. We now reach the Mesozoic or middle age of organic life. Mammals, which are the highest group of Vertebrates, are older than the birds; they first appear in the Trias, the period preceding the Jurassic.

The history of plants also suggests progress ; the oldest known forms are algae. These were followed by Crypto- gams (e. g. Ferns), these by Cycads and Conifers, and these in turn by the Phanerogams or flowering plants. This sequence accords with the systematic position accorded to the various groups. Yet there are numerous exceptions. The Liverworts, a lowly group, are not known from the woods of the Carboniferous epoch, but first appear in the Tertiary strata. Mosses first appear in the middle of the Mesozoic period, and they occur in large numbers in the Tertiary.

The whole question of progress in the organic world is thus of extreme complexity. The science of palaeontology owes its origin to Cuvier ; to him we owe the two suggestions: firstly, that extinct animals do not belong to the same species as living animals, and secondly, that there is a distribution in time of organic forms. He also originated the hypothesis that there has been progress in the world of living organisms. But he was much influenced by the story of the Deluge. He held that all the 'catastrophes' that he postulated had occurred within a comparatively short space of time ; that man had been in existence before them, living in some unknown corner of the world a corner probably later submerged.

He also suggested that the succession of both the human and animal inhabitants in our part of the globe was due to a series of migrations into that area from the original home. Cuvier felt that the Story of Creation did not furnish a satisfactory explanation of palaeontological facts, and he sought to overcome these difficulties by this theory of migration a theory which probably did not entirely satisfy its formulator. His successors accepted his theories without having followed their growth ; hence they were unaware of the emptiness of the word 'Creation' as he used it. Many of them, as for instance d'Orbigny and Agassiz, did not find any difficulty in assuming that there had been a sudden new creation en bloc after each catastrophe !

Bronn, the German palaeontologist, had successfully attacked this idea before Darwin's time. He had demon- strated that some fossils continue from one formation to another, while there is a continual dying out of old forms and a creation of new ones as we follow the fossil remains from stratum to stratum. But few dared ask how the creation of these various forms of life, or of the whole living Universe, came about. They felt that human under- standing was powerless to attempt an explanation too much was known of Nature's impenetrable mystery and of her infinite power.

Then came Darwin. Adopting Lyell's theory of gradual changes in the earth's crust, he taught that life has con- tinued since its beginning in one unbroken stream, and that the origin of new forms and extinction of old ones can be explained without invoking any factors which surpass human understanding. Many of the palaeontolo- gists of the time regarded the theory almost as a personal insult! In no branch of science was it given a cooler reception. They had declared that the problem of the origin of new forms was wrapped in absolute mystery. Darwin affirmed that English cattle-breeders had long ago found out how new species can be obtained. Nature, in producing new forms, follows the methods that are

used in England for breeding sheep ! l The theory was rejected by de Beaumont, Barrande, Pictet, Fraas, Heer, Bronn, Giebel, Waagen, Fuchs, d'Archiac, Owen, and Forbes. They were not all against the suggestion that one form may possibly be transformed into another ; but they objected to Darwin's interpretation of the causes which lead to the origin of new species. The following objections to Darwin's theory are the most important that were brought against it by palaeon- tologists.

(a) In the history of the earth we do not find a regular, continuous, and progressive series of changes leading to the transformation of organisms. There have been rather periodically recurring transformations; long periods of comparative stagnation have alternated with shorter periods of change. (b) We come to certain times when the majority of the existing forms suddenly disappear. These are replaced just as suddenly by a new fauna. The members of this fauna are not directly related to their predecessors. One form is substituted for another, not transformed into another.

(c) Extinct forms do not bridge the gaps in the series of living forms ; they are not truly transitional. The series of animal forms, however far we follow it back, does not narrow down to some single type hidden in some primitive rock. For the most part the extinct forms merely make the series of existing forms more complete, even as the American fauna supplements the European. (d) Since the Deluge, all species have remained constant ; no new ones have been created.

(e) Darwin underestimated the completeness of the geological record. How could we distinguish between palaeontological genera and species if he were right in assuming that only a small portion of the continuous stream of living organ- isms has been preserved by chance from a continual 1 This sense of insult is very clearly seen in d' Archiacs Kritik der Darwiniscben Tbeorie. series ? Do we not in fact find hundreds or thousands of one and the same form in any fossiliferous layer ?

These objections were soon satisfactorily answered by the Darwinists, and henceforth Darwinism dominated palaeontology, as it dominated so many branches of science. Darwin was convinced that history does not represent an evolution of ideas, but merely a succession of material bodies. Applying this thought to palaeontology, he re- garded it as the study of the continuous succession of separate plant and animal bodies. It is as if an historian omitted from his story any account, let us say, of Greek culture, of Roman republicanism, or of the Wandering of the Nations, disregarding these as mere empty ideaology ; and as if he wrote a history of Man, in which all that was stressed was where each individual was born, how long he lived, and how many children he had ! The Darwinians see reptiles predominant in Mesozoic times, and replaced by mammals in the Tertiary. They take each separate type of reptile, each type of mammal, and seek its ancestral form. The aim of every inquiry is the construction of a genealogical tree, and anatomical characters are relied upon for these trees. It is therefore easy to understand why the Darwinian palaeontologists have laid so much stress on the incompleteness of the record.

'If we knew all the extinct Floras and Faunas, the evolu- tion of the organic world would be clearly revealed to us.' Variations of this theme are to be found in the writings of most palaeontologists in those of Darwin, Steinmann, Zittel, Neumayer, and many others. Historians do not speak thus. They do, of course, com- plain of the deficiency of the documentary record, but there is no desire to lay too much stress upon such deficiencies. The documents are regarded as so much evidence; historians examine them carefully and so in- crease our knowledge of the past. The palaeontologist, however, does not discuss the record ; he does not regard it as 'documentary' in the historian's sense. His records are actual bits of that history ; hence the palaeontologist does

not make any distinction between the actual history and the scientific study of that history. There are various palaeontological series which have be- come extremely important, and which, by reason of their supposed completeness, are never omitted from any book devoted to Darwinism those, for example, which illus- trate the evolution of the horse, of the Ammonites, and of various snails. These have undergone very drastic criticism at the hands of Fleischmann. 1 This criticism has not been refuted, and the drift of it is easily understood. We have no idea how one form is changed into another ; whether according to Darwin's rule of gradual evolution, or, as Cope has suggested, by a change in the characteristics, now of the species, now of genus, at another time of the order. How then can a genealogical tree lay claim to any sort of accuracy ? it is based merely on the similarity between certain bones! We must, in the end, ask our- selves, what is gained even if we are able to prove the correctness of these genealogical trees ? Has palaeontology no higher aim than to try to discover from which kind of animal each organism is descended ?

Darwinism was lauded as having thrown a new philoso- phical light upon biology. Yet it would be a mistake to suppose that the science was absolutely changed by this innovation. Morphology, embryology, palaeontology, systematic biology all those fields, in short, which were the first to be affected by the revolution, have remained the same dry classificatory text-book sciences as they were formerly. Palaeontology is a great offender in this respect. It professes to tell us the history of organic life history, vitae magistra, a subject with innumerable appeals to the imagination and the aspirations of mankind ! Palaeonto- logy commands the same weapons. She deals in millions of years. Enormous catastrophes reveal themselves. The traces of remarkable floras and faunas are discovered. Who can remain unmoved as these are unveiled ? Yet a book