Theories of Mental Evolution in Comparative Psychology:
Darwin to Watson

Tolman, C.W. (1987a). Theories of mental evolution in comparative psychology: Darwin to Watson. In E. Tobach (Ed.). Historical Perspectives and the International Status of Comparative Psychology (pp. 15-23). Hillsdale: LEA.

Theories of Mental Evolution in Comparative Psychology:
Darwin to Watson

Charles W. Tolman
University of Victoria, Canada

I have expressed the view elsewhere (Tolman, 1982) that Comparative Psychology's health would be considerably improved if it took its evolutionist foundations more seriously. In its present condition, the discipline displays a puzzling historical irony. Its roots are firmly embedded in evolutionist movement of the mid 19th century -indeed Charles Darwin himself can be claimed as a legitimate parent- yet it has harbored, defended, propagated, succumbed to some of the most antievolutionist thinking of all the biological disciplines. My intention here is to investigate how the founders of our discipline conceived of evolution, in the hope of illuminating our current problems.

The publication of The Origin of Species in 1859 marks one of the most significant revolutions in the history of scientific thought. The changes in thinking that Charles Darwin introduced have in the intervening 125 years become sufficiently widespread in acceptance as to become largely taken for granted in much of our current thought. It is therefore useful to remind ourselves of the major features of that revolution.

Although essentialism (the belief that things are only imperfectly patterned on an eternal idea or archetype) had shown distinct signs of losing its hold on scientific thinking already in the 18th century, it was only put conclusively to rest by the acceptance of the evolutionist understanding of nature. This has innumerable consequences on thinking in general, including the shift from an emphasis on types as a goal of scientific investigation and cognition, to an emphasis on individuals in populations, i.e., so-called "population thinking." The acceptance of evolution also forced the move from a static worldview to one that was dynamic. Science could no longer theorize except in terms of change, development, and process: it became self-consciously historical. [p. 16]

These and many other monumental shifts in the scientific worldview were brought forcefully together in Darwin's central idea of the transmutation of species. In contrast the previously long prevailing view that species, although taxonomically classifiable according to degrees of similarity, represented fundamentally immutable kinds, types, or qualities, the evolutionist asserted the fundamental mutability of species, and therefore also of kinds, types, and qualities. The unity of nature was no longer attributed to an abstract divine Good, but to a concrete process of organic development. Any species now could only be accounted for by the process of its transmutation from another species. The exclusive isolation all natural categories was relegated to the scrap heap of historical misunderstanding. As Ernst Mayr (1982) has concluded: "A true theory of evolution must postulate a gradual transformation of one species into another and ad infinitum" (p. 352).

Darwin's ideas about mental evolution stand in marked contrast to his theory of the evolution of species. In Darwin's discussion of the evolution of mind any concept even resembling the transmutation of species is conspicuously absent. In brief, by Mayr's criterion for true theories of evolution, Darwin's theory of mind does not qualify.

Darwin's concept of mind was a loose one and included three relatively distinct classes of attributes that he called reflex action, instinct, and intelligence. These three classes of attributes were thought to be hierarchically related, but Darwin was emphatic that they were not sequentially related; that is, instinct did not evolve from reflex action, and intelligence did not evolve from instinct. In even the lowliest animals there exists at least some degree of each. A curious exception is Darwin's concept of "lapsed intelligence" according to which an intelligent act could become transformed into a instinctive one.

What then is imagined to occur in mental evolution? It will be useful to note here that Darwin appears to have been naively Cartesian in his metaphysics (Carter, 1898). He believed that mind and body were two distinct, interacting, interdependent realities. But mind, like body, has survival value and is shaped by natural selection. For example, rats with a higher degree of cunning are more likely to survive and will thus be selected for. The conception of change involved here, however, is not that of transmutation. It is a change not of kind, but of degree. In places, Darwin (1888) was quite explicit about this: "There can be no doubt that the difference between the mind of the lowest man and that of the highest animal is immense….Nevertheless the difference…., great as it its, certainly is one of degree and not kind" (p. 127). If Darwin imagined any psychological difference in kind to exist between man and the lower animals -and most of what he wrote suggests that he did not- he failed to provide any theory of how such differences developed. It appears he felt that attributes such as reason had to be there from the beginning in order to be selected for. This is implied by Darwin (1859) in the following: "I have nothing to do with the origin of the mental powers, any more than I have with that of life itself. We are [p. 17] concerned only with the diversities of instinct and of the other mental faculties in animals of the same class" (p. 207).

It seems odd that a theory that made history by its bold assertion that homoiothermic beings evolved from nonhomoiothermic beings, and that flying creatures evolved from nonflying creatures, could not take the implied next step to assert as well that living and thinking beings evolved from nonliving and nonthinking predecessors. Darwin's metaphysics appears to have contained two fundamentally exclusive categories of qualities, one subject to transmutation and one not. This is disappointingly inconsistent and arbitrary, but it is not surprising in view of his Cartesianism.

Herbert Spencer's position (Spencer, 1899) was virtually the same in this matter as Darwin's:

"in Instinct the (adjustive) correspondence is between inner and outer relations that are very simple or general; in Reason, the correspondence is between inner and outer relations that are complex, or special, or abstract, or infrequent. But the complexity specialty, abstractness, and infrequency of relations, are entirely matters of degree" (p. 453).

It was the monistic materialist John George Romanes, the follower of Darwin and Spencer, who can be credited with the first "true" theory of mental evolution. In the words of Carter (1899):

"Romanes had taken upon himself the task of elucidating a theory of mental development in which the genesis of mind is to be traced from non-mental elements, i.e., from instinct and reflex action and, indeed, from physiology itself. This evolutional theory attempted to do for mind what Darwin had done for species, to show a graded series from lower to higher, and a continuity in that series by means of natural inheritance" (p. 115).

Although Romanes adopted Darwin's threefold classification of reflex action, instinct, and intelligence (or reason), these were now understood as forming an evolutionary series, and, equally important, reflex action and instinct were no longer considered as part of the mental, i.e., mind. These two lower categories served as the nonmental from which the mental evolved. According to Romanes, the physiological function underlying this development, was selective excitability or the power of discriminating between different kinds of stimuli.

Romanes's theory of actual transmutation from one level of psychic development to another is not particularly satisfactory. The transition from reflex action to instinct, for example, occurs when into the former "is imported the element of consciousness" (quoted in Carter, 1899, p. 110). Reason evolves when instinctual adaptation becomes "intentional" (Carter, 1899, p. 110). Presumably the underlying mechanism of change is natural selection, but all in all, the theory remains sketchy, speculative, and weak. It was, however, an important recognition of the need for a theory of mental origins and development. [p. 18]

One further innovative recognition by Romanes should be noted. This was his allusion to the possibility of a qualitative distinction between biological and cultural evolution within a monistic metaphysic. He believed that the "art of writing" formed the basis of this distinction. Romanes (1916) wrote that owing to writing:

"a civilized man inherits mentally, if not physically, the effects of culture for ages past, and this in whatever direction he may choose to profit therefrom. Moreover… in this unique department of purely intellectual transmission, a kind of non-physical natural selection is perpetually engaged in producing the best results" (p. 33).

The distinction may be crude, but it is a necessary one, and it is one that could only be made because Romanes took seriously the centrality to evolutional thinking of the transmutation of qualities.

Qualitative transformation was central as well to Conwy Lloyd Morgan's thinking on mental evolution. To begin with, mental evolution was placed within the context of a general evolutionary scheme consisting of three qualitatively distinct, yet sequential and continuous, major stages: inorganic, organic, and psychical.

Morgan's version of psychical evolution is complicated by his insistence on a double-aspect form of psychophysical monism. This meant that the conscious aspect of the psychical could not have evolved from the organic substrate. Rather, only the physiological aspect was thought to have so evolved. The conscious aspect could only have developed from something like itself, and thus Morgan postulated an infraconsciousness associated with the organic. Morgan was most insistent, however, that his position was not pan- or even bio-psychistic. Consciousness evolved not from other forms of consciousness, but from some form or other of what he called metakinetics, which accompany, in Spinozist fashion, the kinetics characteristic of all physical matter: Consciousness is a qualitatively novel transmutation of preconscious metakinetics.

Consciousness was understood as having undergone three stages of evolutionary development. The most primitive of these he called "sentience" that was regarded as a "mere accompaniment of organic behavior" (Morgan, 1900, p. 61). The animal behaves primarily instinctively but is in some sense aware of its environment and its own behavior. Morgan's conclusions about this stage (Morgan, 1900) appear to result more from the philosophical considerations mentioned previously than from empirical evidence: "There may be sentience which is merely an accompaniment of organic action without any guiding influence on subsequent modes of behaviour. In that case it is not effective; and whether it is present or not we have no means of ascertaining" (p. 43). From an empirical point of view, then: "we may assume that this sentience is a concomitant of all life processes, or only of some. But we have no criterion by which we can hope to determine which of these alternatives is the more probable" (p. 61). [p. 19]

The stages of "effective consciousness" were more subject to verification and investigation. The first of these Morgan called "consentience," sometimes also referred to as the "perceptual" stage because percepts were formed that led to perceptual inference. The common manifestations of this stage were the apparently intelligent actions of the higher animals. Here consciousness guided behavior, but behavior was not under the direct control of consciousness.

The second and highest stage of effective consciousness was called the "ideational" or "conceptual" stage, characterized by conceptual inference or abstraction and by the direct control of behavior by consciousness. This was the stage of "reason," as opposed to mere intelligence, and was exclusively attributed to humans.

Morgan (1900) was less explicit about the actual process of transmutation. With regard to origin, in one place he wrote: "The origin of consciousness, like that of matter or energy, appears to be beyond the pale of scientific discussion" (p. 61). Elsewhere, and obviously in a more speculative mood, Morgan (1890/1891) wrote: "I think that we may fairly believe that some dim form of discrimination is the germ from which the spreading tree of mind shall develop" (p. 338).

He was not much more informative about the interstage transition once consciousness appears on the scene. He appeared certain, however, that the transition from the perceptual to the conceptual stage is brought about by the introduction of language. In this connection Morgan (1900) indicated how he imagined the problem will be solved:

"If we were ever to trace the passage from the instinctive through the indicating stage of communication, and so onwards through the beginnings of description to its higher levels, and thus to the use of language as a medium of explanation; it must be through child study. In every normal human child the passage does actually take place, though, no doubt, in a condensed and abbreviated form as an epitomized recapitulation in individual development, of the steps of evolutional progress. Thus we may obtain a key to the solution of one of the most difficult problems in evolution by continuous process -that of the transition from animal behaviour to human conduct" (p. 337).

The scarcity of details regarding the actual process undoubtedly reflected Morgan's cautious recognition that comparative psychology was yet an infant science. But the general conception of the process was clear. It was a qualitative leap from one distinct stage to another by what in his earlier works he called "selective synthesis" (e.g., Morgan, 1894, chap. 19), and that later became more refined under the rubric of "emergent evolution" (Morgan, 1931).

Quite independent of the particular scientific or philosophical merits of Morgan's comparative psychology, there can be no denying that its intent was evolutionary in the truest sense of the word.

The next figure to be considered in the present account, the mechanistic [p. 20] materialism of Jacques Loeb, marks a decided beginning of the end to the evolutional preoccupation among comparative psychologists.

On the one hand, Loeb believed in evolution and was a vigorous opponent of special creation and other mystical accounts of animal origins. He even advanced the idea that what people called conscious or psychic, though it did not exist as such, did exist as associative memory, which was the unique product of increased complexity of the nervous system in higher animals. This hypothesis was further reinforced with a theory of discontinuous emergence similar to that of Morgan (Loeb, 1900, p. 252).

On the other hand, however, Loeb was not a Darwinist and was generally skeptical, if not overtly contemptuous, of the evolutional speculations of his contemporaries. In his 1916 book, The Organism as a Whole, he devoted a single chapter of less than three pages to the topic of evolution. His message was simple: He would believe it when some evolutionist could demonstrate an actual transmutation of species -preferably in the laboratory.

Even Loeb's concession to emergence soon broke down. Loeb (1900) stated:

"We, of course, concede that the associative memory shows different degrees of development or perfection in different animals. These different degrees are mainly differences in capacity and resonance. By difference in capacity I mean a difference in the number of associations of which the brain is capable. By difference in the resonance I mean the ease with which associations are produced" (pp. 253-254).

Quality here was reduced to quantity, a manifestation of the intellectual tendency of Loeb's that so clearly distinguished him from Darwin, Romanes, and particularly Morgan. This tendency was reductionism. The psychic was first reduced to association, but only to make it accessible to a more fundamental analysis: "We consider it our aim to work out the dynamics of the processes of association, and find out the physical or chemical conditions which determine the variation in the capacity of memory in the various organisms" (Loeb, 1900, p. 287).

Loeb could not have been anywhere near as disappointed at Herbert Jennings' discovery of associative processes in the most primitive organisms (Jennings, 1906) as Robert Yerkes suggested in 1905.

The reductionist trend continued with Edward Thorndike. He described his comparative psychological task as follows (Thorndike, 1911):

"If we could prove that what we call ideational life and reasoning were not new and unexplainable species of intellectual life but only the natural consequences of an increase in the number, delicacy, and complexity of associations of the general animal sort, we should have made out an evolution of mind comparable to the evolution of living forms" (p. 286).

This reductively quantitative view of development, Thorndike (1911) felt, was born out by the existing evidence of his time. He concluded: [p. 21]

"In man this increase reaches such a point that an apparently new type of mind results, which conceals the real continuity of the process. This mental evolution parallels the evolution of the cell structures of the brain from few and simple and gross to many and complex and delicate" (p. 294).

And finally: "[Man's] sense-powers show no new creation. His intellect we have seen to be a simple though extended variation from the general animal sort" (p. 294).

John B. Watson's understanding of evolution is well known. Citing Jennings (1906) in support of his views, Watson (1914) concluded:

"No new principle is needed in passing from the unicellular to man. As we pass from the responses of the simple organisms to the more complex one of the higher animals we find (1) a greater number of units, and (2) more complex forms of combinations of these units" (p. 318).

There is for Watson, however, a significant difference between man and "brute," and this is language. But this should not be construed as a difference in principle. Watson (1914) stated:

"we will suppose that future analysis will enable us ultimately to show that every word, syllable, and letter, whether spoken or thought, produces a characteristic form of response which, when recorded, must be looked at from the same standpoint which we adopt when looking at habits elsewhere" (p. 328).

With Watson questions of qualitative transformation and of the special status of the human species succumbed completely to the essentially antievolutional program of reductionism.

I close with the following six conclusions and four observations:

1. We have encountered two distinct conceptions of evolution. The first, represented by Romanes and Morgan, emphasized emergence, transmutation, and discontinuity in the evolution process, although not, it seems, at the immediate expense of continuity. The second, represented by Loeb, Thorndike, and Watson, emphasized uniformity of principle and continuity, often at the clear cost of discontinuity.

2. Ernst Mayr (1982, p. 341) reminds us that one of the "great challenges" of evolutionary biology has been to "reconcile continuity and discontinuity," i.e., to overcome the historical tendency to take up one in exclusive opposition to the other. The first understanding, that of Romanes and Morgan appears to have been working toward that end. The second understanding, that of Loeb, Thorndike, and Watson never recognized it, implicitly or explicitly, as a desirable or necessary goal. [p. 22]

3. The first understanding, being emergent in nature, was prima facie antireductionist. The second was overtly and aggressively reductionist.

4. Curiously, both Loeb and Watson expressed antipathy toward "Darwinian continuity theory," while providing, themselves, the clearest of examples of theory that emphasized continuity over discontinuity.

5. It is true that the emergentist theories had the tendency, despite the best intentions of Morgan's famous canon, to project human traits onto lower animals. This is not a necessary consequence of their emergentism, however. On the other hand, the reductionist theories appear to have been equally guilty of the reciprocal error of projecting the traits of lower animals onto humans, and this is a necessary consequence of their reductionism.

6. With respect to mental evolution, Darwin appears not to have been a Darwinist. His views on this were most like those reductionists who pronounced themselves anti-Darwinian, and most unlike those who were called correctly, I believe, Darwinians.

To these conclusions, I add the following observations:

1. The Thorndike-Watson style of reductionist continuity theory appears to have become hegemonic in 20th century comparative psychology.

2. This hegemony successfully absorbed whatever opposition might have come from the functionalists and it has resisted any inroads form antireductionist such as T.C. Schneirla.

3. The result of this hegemony has been a de-emphasis on evolution in comparative psychology, with the development of a consequent vulnerability to reductionist attacks from the ethologists and particularly from sociobiology.

4. I suggest that it is time for comparative psychologists to reexamine their commitment to evolutionary principles and, once again, lend serious attention to the questions of mental evolution with a view to strengthening the philosophical and theoretical basis for their scientific efforts.

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