James A. S. Watson

“ The characters of a species are determined, it is tolerably certain, by the constitution of the cell nucleus, and accordingly as this varies from one individual to another, so the characters of the individuals will vary. Now, if simple division were to continue indefinitely, successive generations would be produced on the same plan, and the racial characters would in the main remain constant. But conditions of life vary from time to time and from place to place, and the particular type which succeeds best under one set of circumstances may be ill adapted for another. ”

“ It has been stated, in a metaphor which is perhaps more clever than it is exact, that every animal climbs up its own ancestral tree; and while it would be absurd to say, for instance, that a mammalian embryo resembles successively a fish, an amphibian, and a reptile, still many of the broad facts in the evolution of a race seem to be repeated, in a more or less blurred and indistinct fashion, in the development of the individual. ”

“ The sexually produced individual starts life as a single cell, the fertilised egg. This divides and redivides until a hollow ball of cells is produced, which cells, like those of the Volvox, bear cilia. Although simply spherical in shape, the creature moves by rotating round a definite axis, like a planet. Moreover, nutriment is absorbed not by any or every part of the surface, but only by a small area round the lower pole. Now as development proceeds, the cells at this pole divide more rapidly than the rest, with the natural result that the ball begins to get out of shape. ”

“ A typical cell is illustrated in Fig. 16. It consists of a mass of protoplasm, with a distinctly differentiated portion called the nucleus. The function of the nucleus is that of directing and controlling the activities of the cell; if it is removed, the remaining portion of the cell soon dies; while, on the other hand, a small portion of the cell, if it contains the nucleus, may frequently live, and build up new protoplasm to replace what was lost. Cells are formed only from previously existing cells, by a process of division, which is usually simply one of halving. ”

“ The plant has neither the necessity to go forth in search of its food materials, which nature brings to it, nor has it to spare of its painfully collected energy for the labour of locomotion. Hence it remains stationary. The animal must of necessity go to seek its more elaborate fare, therefore it moves. Moreover, to be successful in its search, the animal obviously requires a nervous system to direct and control its movements, which system, except in the simplest and crudest forms, is absent from the plant. ”

“ Thus there can be no reasonable doubt that man has evolved from an ancestor which, if it existed to-day, we should without hesitation class as an anthropoid ape. Could any doubt have remained, it would have been set aside by the discovery, in 1891, of a being occupying a position about midway between the highest apes and the most primitive known man. This is the Pithecanthropus, whose remains were discovered in Java in a volcanic deposit of somewhat doubtful age, but probably belonging to an era when a primitive type of man was already in existence. ”

“ In short, there is hardly any obvious character that has not, in one or other of the breeds, undergone great modification. As Darwin remarked, any naturalist coming upon such a group of forms in nature would have no hesitation in placing them in different species or genera, or even perhaps in different families. Even granting that the conditions of domestication are peculiar, we must admit that if such large changes can occur in a few centuries, it is possible that man has evolved from the lowest of living organisms during a period some hundreds of thousands of times as long. ”

“ The Amphibia are the oldest and the lowest group of vertebrates that are able to lead an active existence on land, and the characters which distinguish them most definitely from the fishes are all to be interpreted as adaptions to the new mode of life. One of the most obvious external differences between the two groups is in the structure of the extremities, the fish having fins, while the amphibian has limbs constructed on the same general lines as our own arms and legs. ”

“ An entirely new type of organ had therefore to be evolved, and this occurred on the same lines as in the Dipnoi, by the development of a pair of sacs from the upper part of the digestive canal, in which the blood is made to circulate, and which are kept filled with air taken direct from the atmosphere. It is of course very well known that an ordinary amphibian is not a lung breather throughout its whole life. The metamorphosis of a gill-breathing tadpole into a lung-breathing frog, illustrated in Fig. 85, is a phenomenon with which everyone is familiar. ”

“ The digestive system is highly developed. The mouth is provided with a jaw or jaws, and with a tongue-like ribbon, which is covered with rows of teeth, like a file, and by whose action the food is torn and disintegrated. A gullet leads from the mouth to a stomach, [68] which is followed by an intestine. Salivary glands and a large hepatic gland or liver are present. Respiration occurs partly through the skin, but special organs also exist for this function, gills in the water forms, and a lung cavity in those which breathe air. There is a well-developed blood system, and generally a heart ”

“ It has twelve pairs of ribs, the same number as in man, and one fewer than in the Gorilla and Chimpanzee.
Practically all the important anatomical distinctions between man and the anthropoids are reducible to two causes: the change from the arboreal existence to a life on the ground and in the open country, and the great development of the intelligence. When the change in the mode of life occurred, it is obvious that an erect carriage would possess an advantage over the stooping gait of the ape, in which it is neither definitely a biped nor a quadruped. ”

“ A very important feature of the reptiles, which they possess in common with the mammals and the birds, is that the embryo produces two membranous outgrowths called respectively the amnion and the allantois, which completely envelop it, and which have important functions in connection with nutrition, respiration, and excretion during the period when the young creature is enclosed in the egg. It is, of course, not until we reach the higher mammals that these membranes assume their greatest importance. ”

“ The Hydra reproduces, for the most part, by a simple process of budding. Small lateral outgrowths are formed, which gradually develop mouth and tentacles of their own. Ultimately these separate and are carried off by the water, later to settle down and become attached to some fixed object. Sometimes, however, sexual reproduction occurs. The reproductive cells are produced, male and female on the same individual, among the ordinary cells of the outer layer. These are set free, fertilisation occurs in the water, and the egg develops in the same manner as that of the coral. ”

“ There is in fact evidence that conditions of civilisation are making for retrogression rather than for progress, a state of affairs that is worthy of the most serious consideration. The only rational and scientific remedy that has been offered for this state of affairs is the institution of some moderate system of artificially guiding man's further Evolution. ”

“ Broadly, however, the majority of physiologists regard life as a highly intricate series of purely physical and chemical processes, and if such a view be accepted, there is no insuperable objection to a general theory of the origin of living from non-living matter. By this it is not intended to imply that the manufacture of living matter is an immediate possibility; for even according to such a theory as we have indicated, it would be supposed that living substance came into being by a very slow process of Evolution, which it is hardly conceivable could ever be repeated in the laboratory. ”

“ The voice is frequently well modulated, and the expression of the emotions, whether by it or by the countenance, is very man-like. The position of the group was summed up by Huxley, after a most thorough investigation of their anatomy, in these words: "Thus, whatever system of organs be studied, the comparison of their modification in the ape series leads to one and the same result—that the structural differences which separate man from the Gorilla and Chimpanzee are not so great as those which separate the Gorilla from the lower apes." ”

“ The small free-swimming cells are the male reproductive bodies or sperms, the others are the female or egg cells. The union of the two produces the fertilised egg, and the process of union is termed fertilisation. In Volvox, the male and female elements are sometimes produced by the same individual, at other times by different ones. Separation of the sexes is no necessary accompaniment of the process of sexual reproduction, and indeed it is only in the higher groups of animals that separate sexes are the rule. ”

“ In brain development the anthropoids are, as already mentioned, greatly inferior to man; in the Gorilla, the largest- [149] brained type, the cranial capacity never, so far as is known, exceeds 600 cubic centimetres, whereas the average in man is about 1500, and the smallest known about 930. Apart from the difference in size, however, there is a surprisingly close similarity between the anthropoid and the human brains, which may be followed even in the particular arrangement of the fissures. ”

“ The nervous system is peculiar; it consists of two nerve cords, the smaller below the gut and the larger above it—the latter therefore occupying a position similar to that of the spinal cord in the vertebrates. Thus in two respects, in its respiratory and nervous systems, Balanoglossus must be regarded as a highly extraordinary member of the worm group, and in both its peculiarities it shows an approach to the vertebrate. There can be little doubt as to the position of this group as an important connecting link between the ordinary worms and the vertebrates. Fig. ”

“ The reptiles have in fact completed the conquest of the land which was undertaken by the previous group, and many of them, living as they do in dry and hot deserts, are as independent of the water as any form of animal life. Thus whereas the amphibian has a thin skin, which is kept moist by the secretions of numerous skin glands, the reptile has a body-covering of scales, which form an effective protection against a too rapid loss of moisture. ”

“ In an ordinary star-fish, which we may take as typical of the group, the mouth is in the middle of the lower aspect, and the excretory opening of the digestive cavity in the upper side just opposite. There is no blood system, or excretory organs, and no concentration of nerve cells into any form of brain. ”

“ The brain development and the intelligence are also much lower than in other mammals, though distinctly superior to those met with among the reptiles. [129] The method of rearing the young in the case of the ant-eater (that of the duck-mole not being yet fully known) is that the single egg is placed, as soon as it is laid, in the pouch under the belly of the female. Here it hatches in a very short time, and here the young animal remains for the first two or three months of its life, being nourished by milk produced by the mammary glands, which open into the pouch. ”

“ The mouth cavity is succeeded by the pharynx, the walls of which are perforated by the gill clefts. Next follow the gullet, the stomach, and the intestine, the division into the three portions being apparent often only after close examination. There are generally gastric glands, of simple form, a large liver, and almost always a pancreas. The kidneys and the reproductive organs open to the exterior by a common duct. A further characteristic feature of the fishes is their external covering of scales. True teeth, comparable to those of the higher vertebrates, appear first in this group. ”

“ Respiration occurs by means of the skin or of gills, or, in air-breathing forms, by 'trachea,' which are small branching tubes opening on the sides of the body. But in no case has the mouth or the digestive tract any connection with the respiratory system, a condition of affairs very different from that obtaining in the vertebrates. The nervous system consists of a brain, situated above the gullet, a nerve ring round the latter, and a double nerve cord running along the body, below the digestive canal. ”

“ Water is continually being taken in by the mouth and passed along this upper canal, to reach the outside by way of the gill slits, and in doing so it passes over the gills, where the blood is circulating in fine capillary vessels. Here the blood is supplied with oxygen from the water, and is at the same time relieved of carbonic oxide. This, it will be observed, is the same method of respiration as that of the fishes. Behind the last gill slit the digestive canal becomes a simple tube, with two digestive glands or liver sacs. ”

“ Between the outer skin and the inner digestive layer is developed a considerable mass of cells, forming muscular and connective tissue, etc. It will readily be understood that the development of such thick tissue masses occasions two distinct new difficulties in the animal economy; for where cells are in direct contact neither with the digestive layer nor with the exterior, their nutrition and the removal of their waste products can no longer be efficiently carried on without special devices. ”

“ Respiration is carried out by means of gills, which are situated in a series of six to eight pouches, each of which opens into the gullet and again directly to the outside, the external openings being an obvious feature of the animal. There is a very distinct, simple heart, which pumps the blood to the gills, from whence it is collected and distributed throughout the body. The digestive canal is a simple tube, provided, however, with a liver and a pancreas, the two most important digestive glands in the higher animals. ”

“ These requirements themselves have so multiplied during the course of social Evolution that innumerable forms of activity have sprung up between those occupations which provide the original necessities of life. The essence of the whole process has been co-operation and the division of labour. ”

“ For as we look around among a number of the most simple forms, we find ourselves handicapped in our attempt to judge between them, by a lack of knowledge of their nature. We come upon organisms so small that they appear, even under the most powerful microscope, only as the tiniest specks ”

“ The broad facts in the history of living things upon the earth are, then, in accordance with the theory of Evolution. The chain of types is indeed a broken one, the gaps being many, and some of them wide. ”

“ There are three living species of lung fishes, one of which is found in Australia, another in Tropical Africa, and a third in the tributaries of the Amazon. All live under conditions which make ordinary respiration by gills difficult. The Australian species inhabits rivers which become reduced, in the dry season, to stagnant pools of foul water, in which ordinary fish frequently fail to survive. ”

“ The nervous system varies greatly, but a pair of cerebral ganglia—a brain—is usually present. There is a particularly keen sense of smell, and taste and hearing may also easily be shown to exist. Some forms are blind, from which condition there is a regular series of stages of development of the eye, up to forms in which it becomes a highly perfected organ, with cornea, iris, lens, and retina. The close similarity between this and the ordinary vertebrate eye, which must have evolved quite separately, is one of the strangest coincidences of Evolution. ”

“ Add to this the fact that locomotion on land presents much greater difficulties than that in water, and it will hardly occasion surprise that vast ages were yet to be required before the Evolution process could produce a land animal.
A striking analogy may be drawn between animal Evolution, from this point onwards, and social Evolution. In the latter case we begin with men, brought by a slow process of Evolution to a high state of individual perfection, living in a state of savage individualism. Each thinks and acts for himself, provides his own food, raiment, and dwelling ”

“ The size of the hemispheres and the wrinkling of their surface are the characters from which we judge the brain development, and it is obvious that in these respects the step from the lower monkeys to the Chimpanzee is greater than that between the Chimpanzee and the lowest human type. ”