Driesch is an embryologist who in his earlier days had enunciated an invaluable analytical theory of development, a theory which suggests that while the formation of the first or elementary organs that appear in the embryo or larva—such structures as the larval gut or sense-organ, or the germ-layers—depends upon the presence in the germ of certain specific organ-forming substances (and this is a fact which has since been abundantly demonstrated by experiment), the origin of parts that appear later in development may be accounted for by the action of the first-formed structures upon one another, these actions being in the nature of physiological responses to stimuli; and for this also some evidence has been produced. On this view differentiation is a mechanical process, set in motion by fertilization or some other cause, and, given a certain initial structure of the germ or ovum, given the presence in it of a certain number of parts or substances capable of acting upon one another with a fixed co-ordination or harmony of the stimuli and the responses, given further a proper constitution of the external environment, then a definite result must follow, the production of an organism which is like the parents that gave it birth.
But in his later treatises this hypothesis has been repudiated, and, by a remarkable volte-face, replaced by a dogma of a wholly different kind. For now it is urged that no merely material factors can possibly account either for the harmony of development—the due co-ordination of mutually reacting parts; or for the secondary harmony of composition—the formation of complex organs by the union of tissues; or for the functional harmony seen in the activities of the adult.
For example, it is asserted that any fragment of an egg of a sea-urchin, if not too small (not less than 1/32 of the egg), can give rise to a whole and normal larva. We are told that the cells of the segmented ovum may be disarranged to any extent by various means, such as raising the temperature, diluting the sea-water, removing the calcium from the sea-water, or by shaking, without prejudice to the ultimate normality of development. Each part of the ovum can therefore, according to the needs of the case, give rise to any part of the resulting organism. ‘Jeder Teil kann nach Bedürfniss jedes.’
And thirdly, when the gastrula of a sea-urchin is transversely divided into two, each half, it is stated, develops into a diminished whole larva in which the gut becomes divided into the characteristic three regions, and all the other organs are formed in correct proportion.
For each of these acts of development in the whole uninjured larva an explanation may conceivably be given in terms of formative stimuli exerted by the originally distinct parts of the egg and calling forth responses in other parts. A mechanism may be thought of which, when set in motion, will achieve a certain end in accordance with its own pre-established harmony; but a mechanism which can be subdivided ad libitum, or almost ad libitum, and the parts of which will still achieve the same end, will still behave as wholes with their parts co-ordinated in the same ratio, temporally and spatially! Such a mechanism is inconceivable; for to ensure the uniform result, the relative amounts and positions of the necessary substances must be imagined as identical in every possible fragment of the egg that is not too small. Something is therefore required to superintend, to co-ordinate the causes of development in the case not only of the part but of the whole egg as well; and this something is not material. A corroborative proof of the inadequacy of the purely material explanation—the causal explanation in the ordinary sense of the phrase—may be derived from a consideration of certain other vital processes. The facts of acclimatization and immunity betray an extraordinary adaptability of the organism to a change in its environment; an organ will adapt itself structurally to an alteration, quantitative or qualitative, of function [Roux’s ‘Functional Adaptation’]; lost parts can be regenerated; and then there is the physiology of the nervous system.
In all these cases of ‘regulation’—and indeed in all other responses to stimuli—the same element, inexplicable in chemical and physical terms, exists and must exist in development. This entity is not a form of energy, but a vital constant, analogous to the constants or ultimate conceptions of mechanics and physics and chemistry and crystallography, but not reducible to these, just as these cannot be translated into one another.
Driesch describes it as a rudimentary feeling and willing, a ‘psychoid’, ‘morphaesthetic’ or perceptive of that form which is the desired end towards which it controls and directs all the material elements of differentiation, like the grain of wheat of Treviranus, dreaming dimly of its destiny. It is thus a vera causa—an unconditional and invariable antecedent—a psychical factor which can intervene in the purely physical series of causes and effects, and for it he revives the Aristotelian term ‘Entelechy’.
Such is the ‘vitalism’ introduced by Hans Driesch, a teleological theory clearly, but no mere metaphysical doctrine of final causes: rather a dynamic teleology which not only sees an end in every organic process, but postulates an immaterial entity to guide the merely mechanical forces towards the realization of that end.
Such a theory is open to very serious criticism from both the scientific and the philosophical side. But before we pass to that criticism let us turn aside to examine some of the other aspects under which the Proteus of Vitalism presents himself.
Thus the modern physiologist Bunge, while owning that it would be a lack of intelligence to expect to make with our senses discoveries in living nature of a different order to those revealed to us in inorganic nature, yet insists that we must transfer to the objects of our sensory perception, to the organs, to the tissue elements, and to every minute cell, something which we have acquired from our own consciousness, something, that is to say, which is not motion, and is not in space, but is in time only.