Biogenesis

“ It marks the natural and legitimate progress of the development. And this in the line of the true Evolution—not the linear Evolution, which would look for the development of the natural man through powers already inherent, as if one were to look to Crystallization to accomplish the development of the mineral into the plant,—but that larger form of Evolution which includes among its factors the double Law of Biogenesis and the immense further truth that this involves. ”

“ If it had no living ancestors, we are thus face to face with the problem of the origin of animal life, either by what has been termed "Abiogenesis" of a merely physical and fortuitous kind, or by creation. This implies the previous production of the complex organic compound known as "Protoplasm," which can, so far as we know, be produced only through the agency of previously living "Protoplasm" formed by living plants. We have, therefore, to presuppose the "Abiogenesis" or creation of plants as predecessors of the animal ”

“ As knowledge of microscopic forms of life increased, so the apparent possibilities of abiogenesis increased, and it became a tempting hypothesis that whilst the higher forms of life arose only by generation from their kind, there was a perpetual abiogenetic fount by which the first steps in the evolution of living organisms continued to arise, under suitable conditions, from inorganic matter. ”

“ The variations in the size of this fraction are the cause of all change in the life-expression of every organism. When the biotone increases, and the metabolism quotient becomes more than one, we have growth; when, on the other hand, it falls below one, and the biotone decreases, we have atrophy, and finally death. New biogens are constructed in regeneration. In generation or reproduction groups of biogens (as germ-plasm) are released from the parent in consequence of redundant growth, and form the foundation of new individuals. ”

“ Such a speck of living protoplasm as the amoeba is known to biologists as a cell; and of such cells or variations of them the structures of all plants and animals are built up, a plant or animal composed of a single cell being known as a unicellular organism, whereas a plant or animal composed of a plurality of associated cells is known as a multicellular organism. Since such unicellular organisms as the amœba are fairly observable, we may conveniently begin the study of life at that stage of evolution which they have reached. ”

“ It is that this universal trait of the Metazoa and Metaphyta, must be ascribed to the primitive action and re-action between the organism and its medium. The operation of those forces which produced the primary differentiation of outer from inner in early minute masses of protoplasm, pre-determined this universal cell-structure of all embryos, plant and animal, and the consequent cell-composition of adult forms arising from them. ”

“ The opposing views of to-day were in existence centuries ago, and they are known in the history of science as the theory of preformation or evolution, and the theory of epigenesis. That most of the great biologists of the seventeenth and eighteenth centuries were decided upholders of evolution was the natural result of the contemporary knowledge of facts. For they knew only the external signs of the process of development. [Pg 2] All they saw was the embryo becoming adult, the bud growing out into a blossom, as the result of a process in which nutrition transformed smaller to greater parts. ”

“ That there has been Evolution in one sense of the term is obvious,—that is to say, development of organic types from lower to higher forms, from the sea-weed or fungus to the oak or the rose, from the star-fish or the coral-insect, to the eagle or to man. The question is, not whether there has been such a{206} progressive succession of forms, but whether one form has proceeded from another genetically, being produced in the same manner as individuals of a species now are. That this has been the case, as Professor Huxley tells us in the same address, is the cornerstone of evolutionary teaching. ”

“ But each unicellular organism would in general inherit the peculiarities, and repeat the life-history of its grandparent-cell, by dividing into two adherent cells. A race of two-celled organisms would thus be established. We may fairly believe that in time a second variation, which also proved fortunate, occurred, whereby the four grand-daughter cells remained adherent until reproduction; and afterwards other variations of the same nature, till an organism was at length evolved which consisted of a multitude of cells adherent together for the common benefit—the morula. ”

“ Hence the invariable character of the germ-cells. In bone-formation, it is clearly shown that special structure begins very early,—in the cell, namely; but it is preserved only where it is aided by the necessary action and reaction. Autonomic in itself, life submits itself to the general laws of evolution. [67] As the direction of motion is determined for whole groups of cells by the direction of the motion of the protoplasm in the single cells, so organic function is determined by the grouping of the irritable, contractile, sensible cells. ”

“ Indeed, as will be seen at the proper time, the mysteries of daily occurrence, such as growth, budding, and reproduction, are as great as any which beset the passage from form to form, from species to species. No one who has thought of it sufficiently can deny that the ordinary facts of generation, as the necessity of the union of two cells of nearly-spent vitality to produce a third cell, or a brood of cells, endowed with primeval vigor, present difficulties more unsurpassable than the origin of the germs of living things from inorganic matter ”

“ The ova of animals, the spores of plants, the isolated cells of lower organisms in general, all show the power of separate assimilation and development. "We must therefore, in general, ascribe to the cell an individual life, that is to say, the combination of the molecules in the single cell does suffice to produce the force whereby the cell is enabled to draw to itself new molecules. The ground of nutrition and growth lies not in the organism as a whole, but in the separate elementary parts, the cells. ”

“ Therefore, natural selection has always to wait and to watch for such variations of germ-plasm as will eventually prove beneficial to the individuals developed therefrom, who will then transmit this peculiar quality of germ-plasm to their progeny, and so on. Therefore also—and this is most important to remember—natural selection as thus working becomes the one and only cause of organic evolution in all the multicellular organisms, just as the direct action of the environment is the one and only cause of it in the case of all the unicellular organisms. ”

“ Thus as regards the function of reproduction some cells subserve it more than others; yet many of the cells of all portions of the whole organism are capable of performing it, for almost any fragment of a sponge, if separated from the parent mass and bedded out, is capable of growing into an "individual" and of continuing the race. If we pass in succession to higher species, we find cell-specialization becoming more and more marked; we find cells becoming more and more capable of performing efficiently some one function and less and less capable of performing all other functions. ”

“ Plants and animals, bones, muscles, and organs of sense, are all composed of modified cells, hardened, flattened, or otherwise altered, as the case may require. If we trace life up to its origin in the individual instead of in the species, we arrive at the same result. All plants and animals, whether of the lowest or highest forms, fish, reptile, bird, mammal, man, begin their individual existence as a speck of protoplasm, passing into a nucleated cell, which contains in it the whole principle of its subsequent evolution into the mature and completed form. ”

“ We may say that variation and heredity are only phases of reproduction, and reproduction is a property of the living cell. We may say that this power of reproduction is dependent upon the power of assimilation and growth, for cell division is a result of cell growth. We may further say that growth and assimilation are chemical processes resulting from the oxidation of food, and that thus all of these processes are to be reduced to chemical forces. In this way we may seem to have a chemical foundation for life phenomena. ”

“ But if such a metamorphosis as this is possible—if the seemingly wide gap between leaf and stamen may be spanned by the modification of a line of organisms—where does the possibility of modification of organic type find its bounds? Why may not the modification of parts go on along devious lines until the remote descendants of an organism are utterly unlike that organism? Why may we not thus account for the development of various species of beings all sprung from one parent stock? ”

“ This marvellous complexity of an osmotic growth may be compared with another fact, the ontogenetic development of the ovum, a single cell which under favourable conditions of environment may evolve into a most complicated organism. These considerations lead to the belief that the beginning of life has not been the production of a simple primitive form from which all others are descended, but that a number of such primitive forms may have been produced, forms which by a rapid physical development attained a high degree of complexity. ”

“ In the lowest forms of cell differentiation the cells of successive generations are all independent; the ontogenetic period consists of a cycle of generations of unicellular plants. Later the cell generations of an ontogeny are united by parts into plant individuals; the ontogenetic period consists of a cycle of multicellular and unicellular, or only of multicellular plant generations. If all the cell generations of an ontogenetic period have been united into a single individual, the successive plant generations are alike and alternation of generations has ceased. ”

“ Protoplasm which has become specialized tissue cannot be generalized afresh, and afterwards transformed into something else; and hence the progress of structure in an organism, by diminishing the unstructured part, diminishes the amount available for making offspring.
It is true that higher structure, like greater growth, may insure to a species advantages which eventually further its multiplication—may give it access to larger supplies of food, or enable it to obtain food more economically; and we shall hereafter see how the inverse variation we are considering is thus qualified. ”

“ The factors of fundamental importance in the study of the theory of Evolution, or the doctrine of the Transmutations of Organisms, are Cells, Heredity and Variation, Environment, Natural Selection, and Isolation.
The evolution of an organism means its descent from preceding organisms with continuous adaptation to its Environment. Its adaptation occurs chiefly, if not entirely, through the Natural Selection of its useful Variations, and the tending of these variations to be transmitted to the offspring by the forces of Heredity. ”

“ Finally, the power of propagation possessed by each separate cell, using the term in its largest sense, determines the reproduction, the variability, the development and renovation of each living organism. No other attempt, as far as I am aware, has been made, imperfect as this confessedly is, to connect under one point of view these several grand classes of facts. We cannot fathom the marvellous complexity of an organic being; but on the hypothesis here advanced this complexity is much increased. ”

“ Here we have a new phenomenon, namely, the setting aside of certain cells in a multicellular individual which from the very beginning are capable of one function alone, namely, reproducing the species. The higher one goes in the scale of life the more striking and [Pg 13] obvious this fact becomes, and as we shall see when we come to the vertebrate kingdom, this setting aside of the cells which are to produce the individuals of the next generation is the key to the solution of the most difficult of our problems. ”

“ And this demonstration has been completed by the final establishment of the cell theory, which involves the admission of a primitive conformity, not only of all the elementary structures in animals and plants respectively, but of those in the one of these great divisions of living things with those in the other. No à priori difficulty can be said to stand in the way of evolution, when it can be shown that all animals and all plants proceed by modes of development, which are similar in principle, from a fundamental protoplasmic material. ”

“ We digressed from this study after having seen that all, even the most complex, multicellular plants and animals, in which the differentiation of the cells into a number of cell-groups with the most diverse functions has attained the highest degree of complexity, are able to produce special cells, the germ-cells, which have the power of reproducing from themselves another organism of the same species, and with the same complex structure. ”

“ Every individual organism from the simple plant known as red snow to the oak, from the zoophyte to man is developed from such a cell. This is unquestionable scientific knowledge. The phenomenal process of organic advancement is through growth of the cell by selective appropriation of material, self multiplication of the cell, chemical transformations of the pabulum of the cell, endowment of the muscular and nervous tissues produced by those transformations with vital and psychical properties. ”