René Dubos

Of Human Nature




From Chapter III of So Human an Animal.



In common usage, the phrase "human nature" refers chiefly if not exclusively to the psychological and moral attributes of man. When used by biological scientists, the phrase denotes, in addition, the anatomical structures and physiological attributes of the human body, both the inherited ones and those that are acquired or modified by experience. Whether used in its limited or generalized sense, the phrase human nature has long been the subject of philosophical and scientific arguments identified with the nature versus nurture controversy.

The view that man is the product of his environment, so forcefully stated by Hippocrates in Airs, Waters, and Places, has long remained influential not only among physicians but even more among philosophers.
John Locke (1632-1704), Jean Jacques Rousseau (1712-1778), and other partisans of the "nurture" theory of human development believed that the newborn child is like a blank page on which everything is consecutively written in the course of life by experience and learning.
In the spirit of this general theory, Rousseau's contemporary Claude Helvetius asserted that, intellectually, man is but a product of his education; Charles Fourier (1772-1837) went so far as to state that universities could at will produce nations of Shakespeares and Newtons!
A century ago, Thomas Huxley (1825-1895) asserted with his usual picturesque vigor that the newborn infant does not come into the world labeled scavenger or shopkeeper or bishop or duke; he is born as a mass of rather undifferentiated red pulp and it is only by educating him that we can discover his capabilities.

In contrast to the partisans of "nurture," Thomas Hobbes (1588-1679), Herbert Spencer (1820-1903) and the social Darwinists upheld the view that nature (heredity) determines to a very large extent the characteristics of the person, young or adult.
On the basis of very inadequate statistical evidence, Francis Galton (1822-1911) concluded that this genetic view accounted satisfactorily for the stratification of English society. As he saw it, judges begot judges, whereas workmen, artisans, and even businessmen were not likely to be born with the innate mental ability required for a successful performance in the intellectual world.
From Joseph-Arthur Gobineau (1816-1882) to Adolf Hitler (1889-1945) and into the present, a narrow interpretation of genetic determinism has given rise to many foolish and criminal attitudes concerning the existence of inferior and master races.

The conflict between genetic and environmental philosophies in the analysis of human attributes has continued into the twentieth century.
Sigmund Freud (1856-1939) believed that the peculiarities of each person's mind can be accounted for by the influences that have impinged on his development, especially those around the time of birth. According to Freud and his followers, most of the complexes that plague man's existence are determined by the early environment.
In contrast, Carl Jung (1875-1961) claimed that man can be understood only by exploring the many factors which played a part in the genesis of the collective human mind during the remote past. He related behavior to the operation of archetypes as old as the human race itself.
Modern discussions concerning the development of languages also center on the genetic-environmental theme. At Massachusetts Institute of Technology, Professor Noam Chomsky teaches that there is an intuitive semantics common to the human species and underlying all spoken languages.
In contrast, the Swiss child psychologist Jean Piaget doubts that this universal grammar is really innate; he points out that speech ability is not present at birth and that speech does not become possible until the major sensory-motor functions have become organized to the point where they are capable of generalization. In Piaget's view, man's universal semantic ability might depend upon the fact that all human beings have similar experiences in early life, leading to the organization and interrelation of the sensory-motor systems.

The nature versus nurture controversy constitutes only a pseudo problem, because, as stated earlier, genes do not determine the characteristics by which we know a person; they merely govern the responses to experiences from which the personality is built. Recent discoveries are beginning to throw light on the mechanisms through which environmental stimuli determine which parts of the genetic endowment are repressed and which parts are activated. Microscopic and chemical studies have revealed the remarkable fact that at any given time in any specialized cell only a limited number of genes are active - 10 to 15 percent of the total gene areas is probably a reasonable figure. This is true of nerve cells as well as of any other type of differentiated cells. Furthermore, genes can be activated or repressed by certain kinds of substances, hormones in particular. It can be assumed that gene activity is profoundly influenced by the composition of the cellular fluids and that various substances differ qualitatively and quantitatively in their activating or repressing effects.

A general hypothesis can now be formulated to account for the well-established fact that the external environment conditions the manner in which the genetic endowment of each person becomes converted into his individual reality. This hypothesis states that the external environment constantly affects the composition of the body fluids, in part by introducing certain substances directly into the system, in part by affecting hormone secretion and other metabolic activities. Such changes in the body fluids alter the intracellular medium which in turn affects the activity of the genetic apparatus. In this manner, the individual's experiences determine the extent to which the genetic endowment is converted into the functional attributes that make the person become what he is and behave as he does.
The biological and psychological uniqueness of every human being generates many conceptual and practical difficulties for the study of behavior and the practice of medicine. Theoretical scientists can make generalizations about man's biological nature, but psychologists and physicians must deal with individual persons. Each person represents a constellation of characteristics and has problems that differ from those found in any other person.

Until a few decades ago, physicians commonly referred to a patient's "constitution" when discussing problems of diagnosis and prognosis. They used the word constitution to denote the person's physical and mental characteristics relevant to his state of health. The patient's constitution was assumed to determine his susceptibility and resistance to stresses and to trauma, as well as his ability to overcome the effects of disease. The term is now rarely if ever used in scientific medicine, because its meaning seems extremely vague. This is regrettable, because much progress has been made toward understanding the factors that determine how a given person will respond to a biological or psychological threat. One definition of the word constitution in Webster's Third International Dictionary is "the whole physical make-up of the individual comprising inherited qualities as modified by the environment."

Early influences certainly play the most important role in converting the genetic potentialities into physical and mental attributes, but it is obvious that these attributes change continuously throughout life. The changes occur as a result of the aging process, and also because physical and mental attributes are constantly being acted on, and thereby altered, by environmental stimuli. To live is to function and to respond. Almost every response of the organism to any stimulus results in the acquisition of memories that alter its subsequent response to the same stimulus. Two organs of memory are now recognized -the brain and the so-called reticulo-endothelial system, which provides the mechanism for a sort of biological memory.

The brain is able to register and store experiences until the time of death. Whether the memory is conscious or unconscious is immaterial for the present discussion. The point of importance is that even subconscious memories can be activated, either by occurrences with which the past events were associated, or by artificially stimulating the proper area of the brain.
The reticulo-endothelial system is a complex of cells widely distributed throughout the body which can bring about tissue changes resulting in the various forms of immunity and allergy. For example, human beings are never spontaneously sensitive to poison ivy; they become allergic to it only after having been exposed. When allergic sensitization has occurred the sensitized person retains the allergy long after the sensitizing event. Human beings susceptible to tetanus toxin can acquire antitoxic immunity by the proper technique of vaccination with this toxin or with a detoxified derivative of it; immunity may wane with time, but some evidence of it persists for many years and probably for the whole life span. Allergy to poison ivy or to any other substance, and immunity to tetanus toxin or to any other poison or microbe, can be regarded as manifestations of biological memory.

Each person's constitution is therefore made up of the evolutionary past embodied in the genetic apparatus and of the experiential past incorporated in the various forms of mental and biological memory. Throughout life, the constitution becomes modified and enriched by the responses that the body and the mind make to environmental stimuli and that become incorporated in the physical and mental being of the person - incarnated in his being, so to speak. At any given time, the constitution of a particular person includes the potentialities that his experiences have made functional; its limits are determined by his genetic endowment. Since the constitution changes continuously with time, it can be defined in scientific jargon as the continuously evolving phenotype of each particular person.


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