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Lecture 12. Great Steps in Organic Evolution.

§ 1. The Origin of Organisms upon the Earth. § 2. The Nature of the First Organisms. § 3. Establishment of Diverse Types of Cellular Organisation. § 4. The Divergence of Green Plants. § 5. The Making of Bodies. § 6. The Divergence of the Sexes. § 7. Progressive Differentiations and Integrations. § 8. Rise and Progress of Backboned Animals. § 9. The Ascent of Man. § 10. General Impressions of Animate Evolution.

THE largest and most overwhelming idea in all science is that the system of Nature in all its complexity, intricacy, multitudinousness, and harmony has come to be as it is from apparently simple beginnings—from something like a nebula if we go back to inorganic genesis, from a crowd of invisible microbes if we begin with the primordial organisms on the cooling earth. We say the word evolution so often that we are apt to get dull to the overpowering grandeur and undeniable mysteriousness of the process. It may not be altogether unprofitable to attempt the impossible,—a short review of the great achievements.

§ 1. The Origin of Organisms upon the Earth.

As every one knows, there was a time when the temperature of our earth was beyond the endurance even of the mythical salamander. It was far too high to admit of the existence of forms of life like those we know, or can even imagine, and we need not speculate about others. There was a time, therefore, when living organisms began to be upon the earth.

Whether germs of living organisms reached terrestrial shores from elsewhere, borne in the crevices of a meteorite or wafted by light waves amid cosmic dust, or whether living organisms may have evolved from not-living material, e.g., from some colloidal carbonaceous slime in which ferments were operative, we do not know. No hypothesis of abiogenesis (i.e., of the origin of the living from the not-living) has yet been suggested that can be accepted with easy-going satisfaction. Whether we start with an inorganic colloid able to utilise solar energy, or with formaldehyde generated by lightning flashes through moist air, or with the cyanogen radicle formed in incandescent materials, difficulties abound. It is not of much avail to point to the achievements of the synthetic chemist unless we can indicate in Inorganic Nature some analogous agency able to pick and choose, combine and eliminate. On the other hand, one is not inclined to lay much stress on the fact that there has not been as yet effected in the chemical laboratories any synthesis of natural proteins, the substances which always form an important part of the physical basis of life; for who would have suspected a few years ago that we should now be using artificially compounded indigo and salicylic acid? More important is it to remember that there is not to be found in natural conditions anything like living matter (or protoplasm) except as organised in the form of organisms or pieces of organisms; that we do not know of a ‘living substance’ as we know of, say, albumen; that the problem is the origin of organisms.

As regards the origin of protoplasm, “the physical basis of life”, as Huxley called it, there is not at present much that can be profitably said. In a letter to Alfred Russel Wallace, Sir W. T. Thiselton-Dyer expressed his sense of the extreme difficulty of the problem. “We cannot form the slightest idea how protoplasm came into existence.” It is not a mere substance; it is an organisation, and when we speak of the complex substances that the chemist makes we should remember that he usually does so by complicated processes. “Protoplasm appears to be able to manufacture them straight off in a way of which the chemist cannot form the slightest conception” (quoted in Alfred Russel Wallace: Letters and Reminiscences. By James Marchant. 1916. Vol. II., pp. 95-8).

If in the future it should become easier for a biologist to say that simple organisms probably evolved naturally from non-living materials, from some colloidal carbonaceous slime activated by ferments, or otherwise; if it should be found possible to make in the laboratory a microscopic material system which lived; what difference would it make to our general thinking save that the domain of the inorganic would appear more continuous than before with the realm of organisms? If it should become easier in the course of this century for a biologist to say that living creatures were probably born of the dust of the earth and the dew of heaven, with the sun shining on both, then would all the groaning and travailing of the inorganic appear more intelligible. Then also it would be clearer than ever that there was in the beginning more than could meet the eye, more than could be summed up in the laws of matter and motion. For no one can conjure ‘mind’ out of ‘matter’, even if he invoke ‘Evolution’ many times.

In ancient days fire was lit from fire, and it was naturally a sacred duty to keep the fire burning. Before the discovery of electro-magnetism, magnets were made from magnets. And until recently crystals were obtained in a crystallisable solution only by the introduction of a nucleus of crystallisation. Thus melted salol, protected from crystals of any kind, remains liquid indefinitely in a closed tube. If it be touched with a platinum wire that has been in contact with solid salol, crystallisation sets in, because a nucleus has been introduced. If the wire be heated first its introduction is without effect. But in 1867, as Professor Dastre (1911) points out, crystals of glycerine appeared spontaneously in glycerine, and have since been spread throughout Europe. No one knows the circumstances which determined their formation, and if they became extinct, as might readily happen, no one knows how to produce them again. In the same way,—this is Professor Dastre's pertinent argument,—the fact that within our knowledge living organism always springs from similar living organism, and that no spontaneous generation of any microbe has ever been demonstrated in any culture-medium, does not warrant us in making a dogma of omne vivum e vivo.

Prof. Lloyd Morgan's position in regard to the origin of living organisms is one that commends itself. “Of protoplasm we may likewise say that under certain conditions, at present unknown, it appeared. Those who would concentrate the mystery of existence on the pin-point of the genesis of protoplasm do violence alike to philosophy and to religion. Those who would single out from among the multitudinous differentiations of an evolving universe this alone for special interposition would seem to do little honour to the Divinity they profess to serve. Theodore Parker gave expression to a broader and more reverent theology when he said: “The universe, broad and deep and high, is a handful of dust which God enchants. He is the mysterious magic which possesses”—not protoplasm merely, but—“the world” (Interpretation of Nature, p. 77).

§ 2. The Nature of the First Organisms.

Regarding the first organisms we know nothing, but biologists who have given a lifetime to the study of cells and simple creatures are able to make certain useful statements. It is quite certain that most of the Protozoa, even everyday forms like Amœbæ and Slipper Animalcules, are the results of long-continued evolution. We may call them unicellular or non-cellular, but they are masterpieces of complexity. The problematical first organisms were not like them. A minute Infusorian called Bellerophon (Penard, 1914) shows on each side a number of prominences like guns projecting from port-holes. Minute cysts may be seen travelling up into these prominences, and there, when occasion demands, they explode into offensive threads. It is plain that Bellerophon is not a simple organism, not a Protozoon in the literal sense.

The late Prof. E. A, Minchin, an expert Protistologist, suggested that the earliest living beings were very minute, possibly ultra-microscopic, units or biococci of chromatin,—the protein material that is characteristic of the nuclei of all cells. Suppose a firm envelope to be formed around one of these chromatin globules, and behold a bacterial type of organism. Suppose the chromatin globules to increase in number and then to show some complexity of arrangement, and suppose a non-chromatinic ground-substance (cytoplasm) to accumulate between them and the envelope, and behold a primitive vegetable unit.

But suppose that around the chromatin granules there was formed an enveloping matrix of restless semifluid substance, rapidly discharging what explosives it got a hold of, in other words living nearly up to its income, and exhibiting streaming outflowings and amœboid movements. This was the first animal, and it preyed on smaller organisms. When the chromatin granules concentrated into and were integrated into a definite nucleus—an organised kernel—the first true cell was formed. The details are all uncertain, but it is probably safe to say that a long journey had to be travelled before even the first cell appeared. It need hardly be said that the numerous suppositions made in this paragraph have a factual basis in existing organisms of low degree.

§ 3. Establishment of Diverse Types of Cellular Organisation.

The next great series of steps had to do with the establishment of a. variety of types of cellular organisation, besides the bacterial and amœboid already referred to. Some active forms evolved cilia and flagella; some sluggish forms evolved protective cysts, adapted to unpropitious circumstances and times; some creeping forms got a skeleton which made them more coherent; others were adapted to flotation; and so on endlessly. A luminous idea was long ago developed by Prof. Patrick Geddes in his conception of the ‘cell-cycle’ that there are three great pathways of cellular evolution—the very active Infusorian-line, the very sluggish Sporozoon-line, and the median compromise of the Amœboid-line. These three lines correspond to the three physiological régimes of lavish expenditure or ‘living dangerously’, of preponderant saving or a life of ease, and of a balance between these extremes. The cells of higher animals may be in part classified on these three lines—ciliated, encysted, amœboid; and there is often, even in man, a transition from one line to another, just as in the life-history of the very simplest Protists, which pass through a cycle of phases without accentuating any one. It is significant that we should see the main physiological possibilities blocked out so early.

We must repeat that if we are asked how there could be in the Primordial Organisms all the promise and potentiality of bee-kind, bird-kind, mankind, we cannot answer save to say that the question is not rightly put. But what we may ask is how the Primordial Organisms contained the promise and potentiality of the next stage in the Systema Naturæ, and it is not so difficult to answer that question.

§ 4. The Divergence of Green Plants.

One of the early great events was the emergence of green plants, possibly from an Infusorian stock. Either they or their ancestors had built up chlorophyll, which is probably the most important single substance in the world, for it is in association with this green pigment that the sunlight becomes available to living matter as a source of energy in building up organic compounds. The divergence of plants and animals was one of the great cleavages in organic nature,—distinguishing those that feed at a low chemical level from those that feed high, the manufacturers of explosives from those that fire them, the savers from the spenders, the predominantly sedentary from the predominantly locomotor, the anabolists from the katabolists, the sleepers from the wakeful, the captives from the free. The contrast between plant and animal is one of the fundamental dichotomies; parallel dichotomies recur many times in the story of evolution,—on to the phlegmatic, imperturbable, fatalistic, hypokinetic type of man and his energetic, excitable, rebellious, hyper-kinetic counterpart.

It is beyond our present scope to follow the plant line of evolution, which went on simultaneously with that of the animal world, the two often intersecting, indeed intertwining. Perhaps the most striking general impression is that of a succession of dominant groups, each of great excellence, each attaining a climax and supremacy and then yielding to another. Thus the gigantic Club Mosses and Horsetails of the Carboniferous forests, to which Man owes so much, yielded to Cycad-like forms and passed into relative insignificance, with little more than pigmy representatives to-day; thus the Cycadophytes in their turn yielded to Flowering Plants.

§ 5. The Making of Bodies.

It was an epoch-making step in organic evolution when ‘bodies’ began to be, that is to say when the transition was made from the unicellular to the multicellular grade of organisation. In some Protozoa the division of the unit is not followed by actual separation, the daughter-units remain associated instead of drifting apart, and thus, coherent colonies arise. In some such way multicellular organisms may have been evolved. It was not increase of size that was primarily important, for many a Rotifer with a thousand cells is smaller than a unicellular Protozoon, such as the Noctiluca which causes much of the phosphorescence of our summer seas. Nor was the step primarily one of increased complexity, either of structure or of activity, for many unicellular organisms are far more complex in plasmic and in skeletal architecture and in their behaviour than are, for instance, the fresh-water polyps, built up as these are of thousands of cells. The establishment of a body was one of the mysterious big lifts in evolution, rising to a new grade of organisation. More scope was given for specialisation of function, and indirectly for increase in size, since free-living single cells cannot grow large except in very peaceful surroundings. Getting a body made great increase in size possible, which, other things equal, counts for something in a rough and callous physical environment, especially if anything aggressive is to be done. One advantage is the possibility of storing energy for vigorous assault on the environment. Another advantage is the possibility of resting and of lying low. Capitalisation has always meant much in evolution.

But the nemesis of gaining a body was liability to natural death,—a liability proportionate to the complexity of the bodily framework. For the more differentiation there is in the colloid substratum in which the chemical processes take place, the more difficult is it for processes of repair and rejuvenescence to counteract that accumulation of wear and tear results which spells senescence (see Child, Senescence and Rejuvenescence, Chicago, 1915).

§ 6. The Divergence of the Sexes.

Another step with far-reaching consequences was the evolution of male and female multicellular individuals within the same species, the two being complementary in the continuance of the race. The first hints of this were among the Protozoa, but these are probably on a side-track. The big fact was the origin of two dimorphic types within the species, a dichotomy like that between plants and animals, probably expressing alternative rates or rhythms of biochemical routine, and culminating in the contrasts between peacock and peahen, ruff and reeve, stag and hind, man and woman. Sexual reproduction meant much in immediate reward. It meant a more economical means of continuing the race; it meant a device for securing the persistence of a successful constitution and for screening the offspring from disadvantageous dints made on the parent's body; it meant more opportunities for re-arrangements of the hereditary items at the beginning of each new life. But the separation of sperm-producers or males and egg-producers or females, differing deeply in constitution, would also tend to increase the possible range of cross-fertilisation, which is often advantageous, and would permit of a very profitable division of labour between the two parents in their relations to the offspring. For the masculine constitution has rarely proved adaptable to mothering. But at a great distance the divergence attained another justification, for sex-dimorphism afforded a basis for love, becoming a liberator and an educator of emotions which have enriched and ennobled the lives of many creatures. It is surely a fact of encouragement to man that there are in the evolution of sex many instances of the sublimation of what was, to start with, somewhat rough and crude, into what, in some birds for instance, it is difficult not to regard as a fine affection.

§ 7. Progressive Differentiations and Integrations.

A multitude of evolutionary steps of great interest must be summed up in the phrase progressive differentiation. Tis-sues begin in sponges, organs in the stinging animals or Cœlenterates. As we ascend the series we see organ added to organ in a way that suggests inexhaustible resources.

The radial symmetry of sponge and zoophyte, jellyfish and coral, well enough suited for a sedentary or for a drifting life, was replaced among the worms by bilateral symmetry, suited for more strenuous life, such as that involved in chasing victims, avoiding enemies, pursuing mates, and shepherding the offspring. This was another literally epoch-making step; it was the beginning of our knowing our right hand from our left. It meant a distinction between head and tail, right and left; it was the beginning of head-brains and cephalisation.

This opened up great possibilities of integration, which means more perfect unity and control, especially through the nervous system. Differentiation may be compared to the extension of an empire and to the complex division of labour that is established in different parts of it; integration is the binding of the whole into harmonious federation and unified control.

This is not the place to follow the long succession of achievements in differentiation and integration which mark organic evolution, but we shall simply mention a few:—an open food-canal, a body-cavity or cœlom between it and the body-wall, striated or swiftly-contracting muscle, a fluid tissue such as blood or lymph, circulatory organs for keeping this in movement and thus distributing throughout the body digested food and oxygen and collecting waste, oxygen-capturing pigments such as hæoglobin, a segmented body as in earthworms, a renewable external armour as in crustaceans, muscular appendages unjointed to start with and by and by jointed, specialised sense-organs such as eyes and balancers and chemo-ceptors, improved respiratory arrangements reaching extraordinary perfection among insects where the blood hardly becomes impure, delicate adjustments for filtering out the poisonous nitrogenous waste of the body, for checkmating intrusive parasites, irritants, and poisons, for dealing with frequently recurrent injuries such as lost arms in starfishes and broken legs in crabs, and so on through a long list.

We can only allude to the establishment of the leading types of architecture which are represented by the various series of Invertebrates or backboneless animals. Besides and beyond the sponges and Cœlenterates already spoken of, we have to deal with a perplexing variety of worm-types; with the higher segmented worms or Annelids, probably leading on to Vertebrates; with the starfishes, sea-urchins, and the like forming the series of Echinoderms; with the jointed-footed Arthropods, such as crustaceans, insects, and spiders, in which instinctive behaviour reaches its climax; with the unsegmented limbless Molluscs, such as bivalves, snails, and cuttles; and many a smaller group besides.

To what purpose such enumeration? Simply that we must bear in mind the fact that millions of years are spent in the fashioning of minutiæ of perfection in types which are certainly not near the highway of evolution that led to backboned animals and eventually to man. Nothing is too remote, too minute, too trivial—everything must be finished and refined. Though it take a million years to make an Argonaut, there is no hurry.

§ 8. Rise and Progress of Backboned Animals.

But a step of great magnitude among many that were eventful was the origin of backboned animals or Vertebrates, which perhaps emerged from an Annelid stock. The origin of Vertebrates meant an independent start on a new line of more masterful life. A dominant feature was the establishment of a relatively large brain protected by a skull and of a long spinal cord protected by the backbone. For there were in this new type of nervous system fresh possibilities of elaborate and subtle integration, of registering experience and experiments on a large scale, yet without interfering with openness of mind, and probably of a richer and freer stream of inner life. It was in Vertebrates first that bone made its appearance, and formed a living internal skeleton pervading the whole body. This contributed not a little to integration. In the establishment of numerous glands of internal secretion, whose hormones or regulative substances are distributed throughout the body, a chemical integration began to operate or to operate on a larger scale (for we know very little of such organs of internal secretion in backboneless animals). It is difficult to exaggerate the importance of these organs in backboned animals, for they are regulatory arrangements which secure smooth working. In one way they make the organism more automatic; in another way they set it free for higher issues. How much is our peace of mind dependent on the insignificant looking speed-regulator, which we call the thyroid gland, or on what the adrenals do in the way of rapidly altering the blood-pressure.

Skulls began with the hags and lampreys—simple gristly brain-boxes to start with; jaws and paired fins, scales and typical gills with the true fishes; digits, true lungs, vocal cords, and a mobile tongue—what a list of acquisitions—with the phlegmatic amphibians; the ante-natal robes (or fœtal membranes) known as amnion and allantois with the reptiles; a four-chambered heart with the crocodilians; warm-bloodedness or keeping the temperature of the body approximately constant with birds and mammals, which also show an enormous advance in brain development,—the big-brain type at length coming to its own. The usually prolonged ante-natal connection between mother and offspring began with the placental mammals; it implied an intimate living together or symbiosis of parent and child that has been of far-reaching importance.

We must remember also how some amphibians achieved what a few fishes essayed, getting foothold on dry land. Most of the amphibian pioneers have to return to the water in their breeding and early development, and the possession of dry land must be put to the credit of reptiles, and associated with what seems at first sight a mere internal detail,—the development of an ante-natal robe that secures breathing through the egg-shell. And just as amphibians mark the transition from water to dry land, which the reptiles perfected, so the extinct flying dragons or pterodactyls pointed from a great distance to that mastery of the air which birds and bats perfected,—each type, however, it is interesting to notice, presenting a different solution of the problem of flight

As we have already seen, the great structural advances are associated with progressiveness of behaviour. Many an infusorian has a very complex life and orders its goings very perfectly, but the range is obviously narrower than that of a spider and the resources are fewer. The behaviour of ants and bees is very complex and on the instinctive line very effective, we may almost say, unsurpassable. But the range is narrower than that of a dog, and the resources are fewer. It is in the big-brained birds and mammals that we find the most convincing evidence of an inner mental life of subjective experimenting, which we call in ourselves perceptual inference or intelligence. Very interesting also is the fact that as an organism attains to more or less intelligent mastery of its environment, it is able to practise reproductive economy. With heightened individuation there is associated lessened reproductivity. There are fewer offspring, which might be racially dangerous were there not a correlated increase of parental care which implies less juvenile mortality. If we read the story aright, the individual counts increasingly, and psychical linkages bind parents and offspring, and kin to kin.

§ 9. The Ascent of Man.

Finally, to bring our breathless survey to its climax, there appeared in the Early Eocene age, perhaps three million years ago, an arboreal race of mammals—the Primates—differentiated from other orders in digits and teeth, skull and brain. From this stock there diverged New World Monkeys and Old World Monkeys, small apes and large apes, until at length there was left a much purified humanoid stem, which after giving off some relative failures eventually realised itself in the modern man stock—“the summit of the whole”.

§ 10. General Impressions of Animate Evolution.

If we try to sink detail and seize the general impression, the dominant one is that of the gradual increase of organisation. This takes varied forms. There is a great deal of structural complexity in organisms that is merely quantitative, but there is a combination of differentiation and integration that is qualitative. The architecture of Venus's Flower Basket (Euplectella) is very intricate, but it does not amount to much more than the endless repetition of a certain kind of scaffolding, where three flinty axes meet at right angles and are firmly warped together where they cross. But compare that kind of intricacy with man's cerebral cortex, which is the chief seat of intelligence. It covers, if spread out, about a foot and a half square and is said to consist of about 9,200,000,000 nerve-cells, which are intricately connected together. Apart from supporting tissue and blood-vessels, these cells and their processes would only occupy about a cubic inch and weigh 13 grammes, but they form the material theatre of our intellectual life, and it is practically impossible to exaggerate the complexity of interrelations,—a complexity on a different plane altogether from that of the Venus's Flower Basket. In the sea-urchin there is, as Aristotle knew, a quaint piece of intricate skeleton, the lantern, which has masticatory, respiratory, and actually locomotor functions. It is a very fine contrivance, which works very beautifully; it consists of twenty-five or more different calcareous pieces and is worked by numerous muscles. But this sort of complexity, finely as it works, is on a relatively low plane compared with, say, our eye or ear—where organisation reaches its zenith.

But the organisation of structure which increases throughout evolution, except in cases of retrogression, is correlated with a complexifying of the internal economy of the body. The variety of internal activities increases, there are more different kinds of metabolism, the subtlety of correlation grows, the different processes work more perfectly into one another's hands. Small bodies near the kidneys secrete from part of their structure a potent substance called adrenalin which is passed into the blood. The amount of adrenalin in our blood is normally about one in 20,000,000 parts; but if we suffer from righteous anger the secretion of adrenalin rapidly increases and like magic prepares us for struggle, affecting the pressure and distribution of the blood, the vigour of the heart, the amount of sugar in the blood, the coagulability of the blood, the rapidity of recovery from fatigue, and so forth. In other words, the organism is subtly correlated not only for the everyday life of the peaceful citizen, but for emergencies when it becomes necessary to return to the ways of our ancestors.

Besides the progressive organisation of structure and the increasing intricacy and correlation there is a complexifying of the inter-relations of organisms. There is a long gamut from having an ocean to swim in and a homestead. The inter-relations of earthworms are not few, but the threads make much more intricate knots in the economy of birds. Many of the simpler animals are related to their environment—whether for food, oxygen, or anything else—in a very generalised way; but evolution has meant an increasing specialisation in the business of exploiting.

We must not forget that alongside of the organic evolution there proceeded an inorganic genesis, changes in which must have meant much to life. In his charming Breath of Life, John Burroughs has stated the idea picturesquely: “Does not man imply a cooler planet and a greater depth and refinement of soil than a dinosaur? Only after a certain house-cleaning and purification of the elements do higher forms appear; the vast accumulation of Silurian limestone must have hastened the age of fishes. The age of reptiles waited for the clearing of the air of the burden of carbon dioxide. The age of mammals awaited the deepening and enrichment of the soil and the stability of the earth's crust—who knows upon what physical conditions of the earth's elements the brain of man was dependent?”

Prof. H. F. Osborn has done good service in reminding evolutionists that their problem concerns four inter-acting complexes of energy:—the inorganic environment, the body of the organism, the ‘heredity-germ’, and the animate environment. How slow we are to learn, for instance, Weismann's lesson that the main steps of evolution are due to changes emerging centrifugally from the germ-cell, not, so far as we know, to changes impressed centripetally on the body. Yet the germinal variations require the aid of somatic functioning if they are to develop fully, and likewise the aid of encouragement from the inorganic environment. Furthermore the animate environment which forms part of the selective sieve is also in process of evolution. It is a correlated fourfold (‘tetrakinetic’) evolution that we have to deal with.

But the crowning feature of evolution is the increased masterfulness of behaviour. Even the very restricted brain development of bony fishes belongs to a different epoch from that of the medusæ under whose umbrella they sometimes shelter, and the otter is as far ahead of the fish as the fish is ahead of the medusa. It is not merely intricacy of behaviour; it is not merely effectiveness; there is plenty of both at very humble levels; the characteristic feature is more freedom, plasticity, and resourcefulness. As we shall afterwards see there is considerable reason for saying—though it is difficult exactly to prove it—that the outstanding fact about organic evolution is the increasing dominance of Mind. As we think of the advance from invisible microorganisms to Mankind, we feel the grandeur of the process. The apparently simple beginnings, dimly discerned by us, have had large issues,—an extraordinarily fine, beautiful, and interesting fauna and flora, an intricate self-regulating and self-compensating system which has a moving equilibrium in spite of the continual breaking-down of parts. The eyes of Man's understanding have been darkened if he does not see something of the majesty of the great becoming.

We see that the length of time required for the evolutionary process has not been, so to speak, a consideration. Half-a-million years may be spent in the fashioning of a feather and longer in giving the horse his hoof. It is certain that the antiquity of man is enormously greater than even Lyell supposed. According to the calculations of experts like Keith and Sollas, it is probable that the human type diverged from the Anthropoid between two and three million years ago. But if it be, as many say, 800 million years since organisms began to spread upon the earth, then the duration of the biosphere has been to that of man as a long forenoon compared with one minute. What fills us with amazement is that so many of millions of years should have been spent, so to speak, in laying the foundations. Without rest, but certainly without haste, the process continued. Well might Bishop Butler say: “Men are impatient and for precipitating things; but the Author of nature appears deliberate throughout His operations, accomplishing His natural ends by slow successive steps.” In modern terminology, “The Tempo of the Absolute is slow.”

Impressive also is the fact that by-paths, leading nowhere in particular, are marked by the same finish as the great highways that approach such notable results as the bee-hive and the ant-hill, or the rookeries and the assemblies of cranes, or the troop of wild horses, or the village community. There are indeed many relatively simple organisms, like polyps, and some old-fashioned primitive types, like Peripatus, but the large fact is the detailed intricacy of the great majority of living creatures. With the category ‘organism’ we must associate a tendency to exquisite finish of complex structure. The living artist does not leave many creations in the sketch stage. “I believe,” the poet said, “that everything is equally perfect.”

It seems to us fair to say that the very broad foundations laid among backboneless animals and among the lower backboned animals like fishes, make the superstructure stable. Let us suppose for a moment—if we do not suppose it always—that the whole process of animate evolution is a coherent thought leading on to Man, who, limited as he is, has some capacity of intelligent appreciation, may it not be that the foundations were and are because without them the superstructure could not stand? That is a matter for interpretation, which is beyond science, and it introduces conceptions of values which are also beyond science. What we venture to emphasise is the fact that without the broad foundations the superstructure could not be. As biologists we do not say that a welter of water-fleas and the like came into being in order that there might be fishes, and fishes in order that there might be fishermen; what we do say is, that, as a matter of fact, the existence of fishes depends on that extraordinarily diversified, prolific, intricate, and beautiful fauna of minute organisms.

We have already referred to the puzzling disappearance of masterpieces, part of the explanation of which is that over-specialisation has its nemesis and that very successful organisms tend to a dangerous exuberance when they get away from the pruning shears of Natural Selection. But it was probably worth losing the giant reptiles to get birds and mammals in their stead. There is little evidence that big inventions once made have ever been lost.

But what must be dominant in our minds after a survey of the achievements of Animate Evolution is that the process has had its outcome in personalities, who have discerned something of its magnificent sweep, who are seeking to understand its factors, who are learning some of its lessons, who cannot rest until they interpret it—even though it be mistakenly.

SUMMARY.

The biggest fact of science is that the Systema Naturæ in all its complexity, intricacy, multitudinousness, and working harmony has come to be as it is from relatively simple beginnings and by successive achievements. By ‘simple’ is meant ‘unevolved’—a nebula or a group of planetesimals, a zooglœa or a bunch of biococci.

Of the origin of the first organisms upon the earth we know nothing,—whether they came from elsewhere or were evolved from some not-living carbonaceous slime activated by ferments. Difficulties beset all the hypotheses of abiogenesis that have been as yet suggested; yet, on general grounds, it seems likely that abiogenesis occurred.

Of the nature of the first organisms we know nothing directly, but it is probable that they were of very minute size and much simpler than most of the Protozoa within the ordinary range of microscopic visibility. Minchin's suggestions leave us convinced that a long journey had to be travelled before the first cell appeared.

The next great step was the establishment of many distinct types of cellular organisation. Perhaps this was the time of the fundamental initiatives.

One of the early events was the emergence and the divergence of Green Plants,—a fundamentally important cleavage, without which the evolution of animals would not have been possible. The vegetative line of evolution is obviously off the main track.

An epoch-making step was the making of ‘bodies’, the transition from the unicellular or non-cellular grade of organisation to the multicellular. It opened the way for specialisation of function, for great increase in momentum, for storing energy, and so on, but it soon brought with it the nemesis of natural death.

Another step of far-reaching importance was the evolution of male and female multicellular individuals, differing in constitution, and complementary in the continuance of the race. This sex dimorphism or divergence had many organic advantages; it became also a liberator and educator of enriching emotions.

A multitude of evolutionary steps must be summed up in the phrase progressive differentiation and integration. Of unique importance was the replacement of radial symmetry by bilateral symmetry which led on to head-brains and cephalisation, and was the beginning of our knowing our right hand from our left. The zoologist discerns that the word epoch-making is not too large for such steps as the making of hæmoglobin, the invention of blood, the establishment of internal surfaces. The story of the evolution of backboneless animals discloses a long succession of achievements.

A step of great magnitude on the main line of evolution was the origin of backboned animals, with a new type of central nervous system opening up fresh possibilities of integration, registration, and experiment. There was a conquering of new media—the dry land and the air. There was a great extension of the range of behaviour and a widening of resources. Economised reproduction became possible as parental care lessened juvenile mortality. The individual became more of an individual and counted for more in life. Psychical linkages bound kin to kin.

Finally, Man emerged, “the summit of the whole”.

Looking back over the great spectacle of Animate Evolution, we gather certain general impressions. There is progressive organisation of structural detail, increasing intricacy and correlation of functions, a complexifying of the inter-relations of organisms, a growing masterfulness and resourcefulness of behaviour.

The process of evolution from invisible Biococci to Mankind has a magnificence which cannot be exaggerated. It has been a process in which the time required has been of no consideration, in which there has been neither rest nor haste, in which by-paths show as much finish as the highways, in which broad foundations have been laid so that the superstructure has been secure, in which, in spite of the disappearance of masterpieces, there has been a conservation of big gains. It has had its outcome in personalities who have discerned its magnificent sweep, who are seeking to understand its factors, who are learning some of its lessons, who cannot cease trying to interpret it.