By this is a living being distinguished from all that our perception or our science isolates or closes artifici- ally. It would therefore be wrong to compare it to an object. Should we wish to find a term of comparison in the inorganic world, it is not to a determinate material object, but much rather to the totality of the material universe that we ought to compare the living organism. It is true that the comparison would not be worth much, for a living being is observable, whilst the whole of the universe is constructed or reconstructed by thought. But at least our attention would thus have been called to the essential character of organization. Like the universe as a whole, hke each conscious being taken separately, the organism which lives is a thing that endures. Its past. Id its entirety, is prolonged into its present, and abides litbere, actual and acting. How otherwise could we under- stand that it passes through distinct and well-marked phases, that it changes its age — in short, that it has a history? If I consider my body in particular, I find that, Uke my consciousneas, it matures little by little from infancy to old age; like myself, it grows old. Indeed, maturity and old age are, properly speaking, attributes only of my body ; it is only metaphorically that I apply the same names to the corresponding changes of my conscious self. Now, if I pass from the top to the bottom of the scale of fiving beings, from one of the most to one of the least differentisr ted, from the multicellular organism of man to the unicellu-
CREATIVE EVOLUTION ichap.
lar organism of the Infusorian, I find, even in this simple cell, the same process of growing old. The Infusorian ia exhausted at the end of a certain number of divisionB, and though it may be possible, by modifying the environ- ment, to put off the moment when a rejuvenation by con- jugation becomes necessary, this cannot be indefinitely postponed.' It is true that between these two extreme cases, in which the organism is completely individualized, there might be found a multitude of others in which the individuality is less well marked, and in which, although there is doubtless an ageing somewhere, one cannot say exactly what it is that grows old. Once more, there is no universal biological law which applies precisely and auto- matically to every living thing. There are only direcHona in which life throws out species in general. Each particular species, in the very act by which it is constituted, affirms its independence, follows its caprice, deviates more or less from the straight line, sometimes even remounts the slope and seems to turn its back on its original direction. It is easy enough to argue that a tree never grows old, since the tips of its branches are always equally young, always equally capable of engendering new trees by budding. But in such an organism^which is, after all, a society rather than an individual — soTuetking ages, if only the leaves and the interior of the trunk. And each cell, con- sidered separately, evolves in a specific way. Wherever anythijig lives, there is, open somewhere, a register in which tiine is being inscribed.
This, it will be said, is only a metaphor. — It is of tic
very essence of mechanism, in fact, to consider as meta-
phorical every expression which attributes to time an
effective action and a reality of its own. In vain docs
' Calkina, Studiet on the lAfe Hiatory of Prolozoa (Archiv ). Entmck- lungutuOamk, voL xv., 1»03, pp. 13Q-1SG].
mmviDUALiTy and age
mediate experience show us that the very basis of our " conscious existence is meraorj-, that is to say, the pro- longation of the past into the present, or, in a word, dura- tion, acting and irreversible. In vain docs reason prove to us that the more we get away from the objects cut out and the systems isolated by common sense and by science and the deeper we dig beneath tliera, the more we have to do with a reality which changes as a whole in its in- most states, as if an accumulative memory of the past made it impossible to go back again. The mechanistic instinct of the mind is stronger than reason, stronger than immediate experience. The metaphysician that we each carry unconsciously within us, and the presence of which is explained, as we shall sec later on, by the very place that man occupies amongst the living beings, has its fixed re- quirements, its ready-made explanations, its irreducible propositions: all unite in denying concrete duration. Change must be reducible to an arrangement or rearrange- ment of parts; the irreversibility of time must be an ap- pearance relative to our ignorance ; the impossibility of turning back must be only the inability of man to put things in place again. So growing old can be nothing more than the gradual gain or loss of certain substances, per- haps both together. Time is assumed to have just as much reality for a living being as for an hour-glass, in which the top part empties while the lower fills, and all goes where it was before when you turn the glass upside down. True, biologists are not agreed on what is gained and what is lost between the day of birth and the day of death. I There are those who hold to the continual growth in the I volume of protoplasm from the birth of the cell right on to its death." More probable and more profound is the
' Sedgwick Minot, On Certain Fhenomena oj Growing Old (Proe. Amer, Anoe. for tJit Advaruxment o/ Science, 39th: Meeting, SoJem, 1891, pp. 271-288).
theory according to which the diminution beara on the quantity of nutritive substance contained in that "inner environment" in which the organism is being renewed, and the increase on the quantity of unexcreted residual substances which, accumulating in the body, finally "crust it over."' Must we however — with an eminent bacteri- ologist — declare any explanation of growing old insufficient that does not take account of phagocytosis?' We do not feel quahfied to settle the question. But the fact that the two theories agree in afRnning the constant accumulation or loss of a certain kind of matter, even though they have little in common as to what is gained and lost, shows pretty well that the frame of the explanation has been furnished a priori. We shall see this more and more as we proceed with our study: it is not easy, in thinldng of time, to escape the image of the hour-glass.
The cause of growing old must lie deeper. We hold that there is unbroken continuity between the evolution of the embryo and that of the complete organism. The impetus which causes a living being to grow larger, to develop and to age, is the same that has caused it to pass through the phases of the embryonic life. The develop- ment of the embryo is a perpetual change of form. Any one who attempts to note all its successive aspects becomea lost in an infinity, as is inevitable in dealing with a con- tinuum. Life does but prolong this prenatal evolution. The proof of this is that it is often impossible for us to say whether we are dealing with an organism growing old or with an embryo continuing to evolve; such is the case,
' Le Danlec, L'IndividuatiU el I'erreuT indirHdualiste, Paris, 1905, pp. 84 ff.
MetchnikoS, La Dtgtniretcenet iinile {Annie biolagique, ii pp. 249 3.). Cf. by the same author, La Nature humaine, Paris, 1003, pp. 312 S.
Ikdividuality and Age 19
P for example, with the larvae of insects and Crustacea. On the other hand, in an organism such as our own, crises like puberty or the menopause, in which the individual is completely transformed, are quite comparable to changes in the course of larval or embryonic Ufe— yet they are part and parcel of the process of our aging. Although they occur at a definite age and within a time that may be quite short, L no one would maintain that they appear then ex abrupto, I from without, simply because a certain age is reached, just i , as a legal right is granted to us on our one-and-twentieth birt-hday. It is evident that a change lilce that of puberty is in course of preparation at every instant from birth, and even before birth, and that the aging up to that crisis consists, in part at least, of this gradual preparation. In short, what is properly vital in growing old is the in- sensible, infinitely graduated, continuance of the change of form. Now, this change is undoubtedly accompanied by phenomena of organic destruction: to these, and to these alone, will a mechanistic explanation of aging be confined. It will note the facts of sclerosis, the gradual accumulation of residual substances, the growing hyper- trophy of the protoplasm of the cell. But under these visible effects an inner cause lies hidden. The evolutioa of the living being, like that of the embryo, implies a con- tinual recording of duration, a persistence of the past in^" the present, and so an appearance, at least, of organic memory.
The present state of an imorganized body depends ex- clusively on what happened at the previous instant; and likewise the position of the material points of a system defined and isolated by sciejice is determined by the po- sition of these same points at the moment immediately before. In other words, the laws that govern unorganized matter are expressible, in principle, by differential equations
[oau.
in which time (in the sense in which the mathematiciao takes this word) would play the rale of independent variable. Is it ao with the laws of Hfe? Does the state of a living body find its complete explanation in the state inunediately before? Yes, if it is agreed a priori to liken the living body to other bodies, and to identify it, for the sake of the argu- ment, with the artificial systems on which the chemist, physicist, and astronomer operate. But in astronomy, physics, and chemistry the proposition haa a perfectly definite meaning: it signifies that certain aspects of the present, important for science, are calculable as functions of the immediate past. Nothing of the sort in the domain of life. Here calculation touches, at most, certam phe- nomena of organic destruction. Organic creation, on the contrary, the evolutionary phenomena which properly] constitute life, we cannot in any way subject to a mathe- 1 matical treatment. It will be said that this impotence' is due only to our ignorance. But it may equally well express the fact that the present moment of a living body does not find its explanation in the moment immediately before, that all the past of the organism must be added to that moment, its heredity — in fact, the whole of a very long history. In the second of these two hypotheses, not in the first, is really expressed the present state of the biological sciences, as well as their direction. As for the idea that the Uving body might be treated by some BUperhuman calculator in the same mathematical way aa our solar system, this has gradually arisen from a meta- physic which has taken a more precise form since the physical discoveries of Galileo, but which, as we shall show, was always the natural metaphysic of the human mind. Its apparent clearness, our impatient desire to find it true, the enthusiasm with wnich so many ejccellent minds accept it without proof — all the seductions, in short,
;irions, in snori, j
INDIVIDUALrFY AOT> AGE 21
that it exercises on our thought, should put us on our guard against it. The attraction it has for us proves well enough that it gives satisfaction to an innate inclination. But, as will be seen further on, the intellectual tendencies innate to-day, which life must have created in the courae of its evolution, are not at all meant to supply us with an explanation of Me: they have something else to do.