Sometimes a collaboration between individuals occupied in separate biological fields and the application of understandings from one field to the other leads to felicitous insights and new perspectives.

Our own experience has encompassed studies of the evolutionary bases of human behavior on the one hand and two decades of clinical experience with addicts of various kinds (and their families) on the other.

Departing from the conventional view that addiction arises solely from the life history of an individual or out of an obscure chemical imbalance, we have come to a formulation of the problem, rather, as one of the effects of group mechanisms upon the individual.

The dynamics residing within the entity we call a society affect all its members. There are those who can adapt themselves to group requirements and others who in some or many ways cannot.

This applies to all social groups of all creatures, whether animal or human. Very frequently manifestations that appear to us to be peculiarly human, when compared with the patterns of life of other animals, come to be thought of as due to our cultural endowment or to our specific civilization and as phenomena that therefore define a separation between our species and all others.

Language, love, politics, and the care of the sick are among many human propensities and predilections that come into this category. Yet everything human has its origin in an animal past, and such a view tends to prevent certain aspects of human behavior from being seen in a context of overall natural patterns, hindering full understanding of their significance.

The problem of addiction is certainly a human one, and it has not been thought of in terms of comparative behavior. The reason is simple.

Addiction does not occur in a natural state. Laboratory animals may be induced artificially to become addicted to most of the substances on which a human being may become physiologically or psychologically dependent, but this does not happen in feral conditions.

Nor, on the other hand, is the presence of “mind” in humans an explanation for the different behavior, since animals with no advanced neocortical development can become addicted in laboratory conditions.

Beyond the failure to view addiction in terms of overall natural processes-- or perhaps a part of that failure--is the tendency we have had to ask questions about the “whys” of addiction in terms only of an addicted individual’s life.

We ask what personal problems led him to turn to drugs or alcohol for relief. Even if we take a step further and examine the social background of the addict, seeking a cause for his problems on a wider basis, this larger dimension is considered relevant only in terms of its effect on the individual; and so the answers we find, like the questions we pose, remain individual oriented. Since the study of the individual is the domain of the psychiatrist, the problems of addiction have come to be accepted as within his province.

A further question that must arise, of course, is how it can happen that addiction can arise biologically. This question has been asked by some, and answers to it have been sought in the physiology of the nervous system.

But this step again focuses on the individual, even when investigations are pursued into his genetic background; and so, while the question is right, the approach to answering it is limiting, since it leads no further than the previous ones--to the individual. Yet it is indeed in neurophysiology that we may begin to find clues to the larger pattern.

The nervous system is more than a recipient of stimuli and regulator of an organism’s behavior. It is a repository of reflex responses that connect the individual to his phylogenetic past and is also a regulator of interactions between the individual and the present society of which he is a part.

What we call social pressures are conveyed to an individual, and he reacts to them, not only through his understanding but also through direct neural responses, so that in this sense the nervous system is the mediator between an individual and a society in a way analogous to the role of the hormones in mediating between the behavior of cells and the needs of the whole organism.

In binding individuals to the needs of their societies, their nervous systems serve to integrate group well-being. To see this clearly, it is helpful to look at some group mechanisms in the breeding groups of other species, and we may then see how these throw light on otherwise puzzling human behavior.

The pioneer experiments of R.N. Chapman (1928) showed that, in an enclosed environment in which the nutrient medium was a layer of flour two centimeters deep, a steady ceiling population of the flour beetle (Tribolium confusum) would ultimately be obtained.

An experimentally repeatable, almost constant density of individuals per gram of flour was finally arrived at, whether the culture was started with one pair of adults or many pairs or whether the volume of flour was small or large.

Of many subsequent workers, D.S. MacLagan (1962) performed parallel experiments with Tribolium and Sitophilus, the grain weevil. He found that there was a drop in the number of eggs laid per female associated with crowding, and he concluded that natural populations as well as experimental ones “automatically check their own increase by virtue of this density effect, and that the organism itself imposes the ultimate limit to its own abundance when all other factors (biotic and  physical) have failed” (p. 452).

Both Tribolium confusum and its close relative T. castaneum, when adult, have glands in the thorax and abdomen that produce an irritant gas that P. Alexander and D. H.R. Barton (1943) identified as ethylquinone. The glands are stimulated to liberate this gas by disturbance and crowding.

In crystalline form, it is lethal to first-instar larvae; as a gas it induces developmental abnormalities in late larvae and pupae, and it probably has a depressing effect on the well-being of the adults (Roth and Howland 1958).

The now classic experiments of C.M. Breder and C.W. Coates (1932) showed that, in tanks containing an equal volume of water, whether a single gravid female or a number of guppies (Labistes reticulatus) were placed in them, it took only about 20 weeks for the same constant population of nine or ten fish to be reached in each.

Surplus individuals were cannibalized. Tadpoles overcrowded in their tanks excrete into the water metabolites that have the effect of stunting growth until the smaller individuals die off and the population is adjusted to an uncrowded condition (Richard 1958).

Socially induced mortality occurs also in birds, and among them social status becomes a factor. The most subordinate members of a population may be inhibited from breeding at all.

Those a little higher in rank may achieve a nest and mate and perhaps even eggs, but when environmental conditions impose a necessity for a reduction in the number of young birds being reared, the stress falls more tellingly on them than on better-established and higher-ranking members of the community.

A wide variety of species-specific mechanisms are brought into play, from reduced egg production or the destruction of eggs to the killing of young, but for our present purpose it is sufficient to note that the reduction of the threshold of resistance to parasitic infestation is one of the many manifestations of crowding stress that have a homeostatic effect.

D. Lack (1954, chapter 54), in an extensive review of mortality attributable to disease in birds, noted that, when they are in good condition, such birds as the red grouse (Lagopus lagopus) can carry a considerable burden of internal parasites without injury but that, if the quality of their staple food plant is affected by harsh weather or by unusually extensive damage by the heather beetle, then the birds’ threshold of resistance is lowered so that the lower ranking appear to die of parasitic disease.

The element of status in the survival of birds in crowded conditions was noted in an extreme manifestation by A.A. Allen (1934). He observed in a captive group of ruffed grouse (Bonasa umbellus L.) what he called an intimidation display. “A bird that has been completely subjugated . . . is subject to attack from every other bird in the enclosure. He has developed an inferiorism and usually, unless removed, he remains in a corner until he dies, not from mechanical injury nor from starvation, but from some sort of nervous shock, and death is likely to occur within 24 hours.”

V.C. Wynne-Edwards (1962) has commented that the function of hierarchy is to identify surplus individuals whenever environmental necessities require a reduction of population. Wild mammals respond no less than other creatures to population density. In North Wales Brambell and his associates made the discovery in the rabbit (Oryctolagus cuniculus) that an average of 64 percent of embryos  conceived perish before birth, usually by the twelfth day of pregnancy.

The arrested embryos are not aborted, but their tissue is broken down and resorbed by the uterus, leaving nothing but an impermanent scar (Thompson and Worden 1956, pp. 112-113). The percentage of embryos resorbed is responsive to environmental conditions.

These are but arbitrary examples (that could be multiplied almost endlessly) taken from insect, fish, amphibian, avian, and mammalian societies, to give some idea of the types of social mechanisms to which we are referring.

V.C. Wynne-Edwards states that there can remain no doubt that populations are effectively self-limiting, “and the inference must be very strong that selection has perfected the adaptations so that population densities always tend to balance themselves at the optimum level” (1962, p. 498).

In his encyclopedic work, he has shown that there is probably no species that does not have some built-in method of population control that effectively regulates the density of its breeding groups or societies. Indeed it is clear that this must be so, since any population that failed to effect this regulation would very soon strip its habitat of the resources necessary for its sustenance and thus promote its own extinction.

For each species, the range of “personal space” required by individuals varies, but the work of such researchers as J.B. Calhoun (1962, 1963) has made us aware of the gross distortions of normal behavior that occur when this space requirement is infringed. The more enlightened curators of zoos have recently come to recognize the modifying effects on the natural behavior of animals of cages that confine their living space too closely, and we ourselves have become aware of our own need for “personal space” and of human responses ranging from mild irritation all the way to violent aggression that may occur when it is invaded.

The potential for these responses is carried genetically in all species, and H. Selye (1950) has shown that social stress can have depressing and injurious effects on the animal body just as severe as those produced by disease, hunger, or fatigue.

But the mediating agency between the environment and the individual is the nervous system, in that the nervous system not only brings awareness of population pressures to the individual but also sets in motion the adaptive responses, whether physiological or behavioral.

We may now ask ourselves, Where does the human being fit into this pattern?

It is evident that no natural design as universal as the response against crowding in the interlocking network of mechanisms that exist in the interest of species viability and survival can possibly be without significance or consequence in our own.

And, indeed, into quite recent times many human practices, including infanticide, gerontocide, social requirements governing marriage, taboos governing child spacing, and so on, have in effect achieved population regulation by cultural means as efficient as the biological mechanisms of other species (Carr-Saunders 1926).

Many observers have noted that tribal groups relatively out of contact with modern life had maintained stable populations over long ages. If this is the case, we must concede that it is hardly possible for modern societies of man to be entirely free not only of vestiges of earlier mechanisms of population control but also of some that operate in our own societies and ‘in our own times.

It is indeed probable that such mechanisms in fact exist but that they appear in the guise of cultural practices or individual characteriological  idiosyncrasies that themselves become the subject of attention and so obscure awareness of the larger function they serve.

This then interferes with our realization that powerful biological mechanisms operate on a group level in our culturally and technologically modified societies, no less than in all societies in the rest of nature.

Doubtless the individuals living in a tribal society would see the observance of their taboos affecting, say, child spacing as acts of conformance with their customary cultural practices and would not relate it to similar behavior in many animal groups.

Would it be possible for us, who are at a distance and not involved with them, to see those practices in terms of their overall biological effect?

May we then not ask ourselves whether some of the social manifestations we see in our own communities and consider to be culturally conditioned may not also fit into larger biological patterns? We believe that this is so and that addiction comes into this category.

From the point of view of the individual concerned and of those who attempt to relieve him of his habit, addiction is an unmitigated ill.

The initial gratifications derived from the drug, alcohol, or smoke frequently fade as an organism becomes habituated and relatively immune to their effects, and the addict is then driven to larger and more frequent intake in order to capture the initial pleasurable feeling.

In this process a crescendo of ills besets him. His health declines, and his social adjustment is increasingly disrupted, until eventually he secedes from his community altogether and lives, so to speak, on its fringes, either as a member of a deviant group or as a solitary outcast.

His fertility is frequently impaired and his genetic endowment thus often eliminated from the gene pool of his population. The personal involvement of medical workers in general and of psychiatrists in particular in attempts to help these individual reverse their downward drift is a factor in the failure to see the overall pattern.

Given our current attitudes about what constitutes sickness and health, focused as they are on the well-being of individuals, perhaps it takes a quantum jump in our thinking to recognize the undoubted fact that a whole breeding group or society is an evolutionary unit in its own right and must also maintain good health if it is to survive.

On the health of its breeding groups the viability of an entire species depends. Here we must note that the general understanding of the principle of natural selection encompasses a misconception: it is that the genes of fit individuals survive, while those of less fit individuals are weeded out over time.

The fact is a little different, but that small difference puts a completely other complexion on the matter. It is that the principle of natural selection does not operate at the level of the individual but at the level of the breeding population as a whole.

At this level it is easy to see that, if every individual within a breeding population were exquisitely adapted to its current environment, then any external change in that environment would wipe out the total population.

It is therefore an adaptive character of populations that they carry in their total gene pool several variations of individual traits, including some that appear currently maladaptive at any given time.

The best-known example that illustrates this fact is the population of moths whose white wings are peppered with grey-to-black speckles. In an earlier period of pristine atmosphere, the whiter moths  predominated numerically in the population.

As industrial pollution darkened the trunks and branches of the trees on which they settled, however, the whiter moths became conspicuous to their predators and were picked off in proportionately larger numbers, until at the present time the populations of this species are predominantly of the darker colored variety (Kettlewell 1973).

Should human antipollution endeavors now prevail, on the other hand, it is likely that the lightly speckled moths will again come into their own. Thus it will be seen clearly that, for this moth population as a whole, it is adaptive for it to carry, if recessively, in all generations a potential for alternative coloration that at any particular time is ill adapted--indeed, dangerous-- for the individuals that carry it.

Without this potential for alternative coloration, the destiny of all the moths would be at the mercy of the vagaries of their habitat, and their species life would be very short. Variation of color in the moths, of course, is an anatomical character.

In our own species from its earliest emergence, however, behavior has been as determinative of survival as morphology and a spectrum of behavioral traits therefore as important to the viability of our species as a whole as morphological variety.

It would seem reasonable to assume that a range of sensitivity to external stimuli and group pressures would have its place in this context and that those who take and become addicted to narcotics or stimulants in our present societies are among the more sensitive to such stimuli and pressures.

In other eras or in other circumstances, such hypersensitivity might well have been and may well yet become a species-saving characteristic. Yet in the universal ability of all groups of all species to reproduce a larger number of offspring than they can sustain and the tendency of all groups to do so lies the necessity that mechanisms must exist to ensure that at all times all populations are, so to speak, thinned out.

Inevitably it is those individuals who are currently of the wrong color, too tall or too short, too slow or too fast, or too little or too acutely sensitive who are the ones who become sacrifices to the need of the group to adjust its density.

Those individuals then, depending on their species, fall prey to predators; to reduced resistance to parasites; to elimination by others before birth, in the perinatal period, or later; or to self-elimination as a result of social pressures.

Within the context of the concept of the well-being of the larger entity, the whole society--its necessity to produce more recruits than it needs so that it may survive in case of calamity and therefore its equal necessity to eliminate its surplus--we discover an overall design into which several conditions that have proved puzzling to investigators may well fit.

For example, no more than the potential addict does the schizophrenic show any organic impairment that could classify his condition as a disease state; and, like the addict, the schizophrenic is also hypersensitive to stimuli and to social signs--above all, to crowding. It would appear probable that both the addict and the schizophrenic are heirs to genetically carried behavioral responses that were supremely adaptive in earlier phases of mankind’s phylogeny when human groups were smalI, when social stimuli were infinitely fewer, and when a creature’s awareness had to be constantly alert and finely attuned to sensing danger from the environment in order to survive (Jonas and Jonas 1975).

A nervous system so exquisitely adapted to perceiving the minutest changes in environmental signals clearly becomes overwhelmed and produces dysphoria when its carrier must exist among the exponentially increased social stimuli of a modern environment. Those individuals  whose nervous systems are less sensitive and who would surely be at peril in, say, a forest habitat today are better adapted to our more crowded living conditions.

The more sensitive can only attempt to ease their discomfort by blunting their perceptions with alcohol or depressive drugs or, alternatively, by using consciousness-altering drugs to transport their senses from the dysphoric world in which they live to private worlds of their own.

In the conduct of group therapy among addicts in connection with the U.S. Army’s detoxification and rehabilitation program, we have observed in practice that the members of these groups consistently show difficulty in relating to each other. They are plainly uncomfortable being together in a group, facing each other, and experiencing the social stimuli implicit in any close human gathering.

Even with those who attempt to dissipate their discomfort in drunkenness, it is apparent that their conviviality or boisterousness does not lead them toward closer interactions with others but is, rather, a device that shields them from it. The alcoholics’ own belief that they drink to relax their sense of tension is misleading.

What they are doing is blunting their perceptions so that they no longer respond to those signals from others or from within themselves that cause them feelings of embarrassment, inadequacy, or shame when they are sober. In doing so they eventually effect a general leveling of their mood, and then, paradoxically, the absence of affect itself produces an unhedonistic and dysphoric state.

Today addicts of whatever kind form a sizable segment of the broad spectrum of our population. As such they provide an available pool of individuals that is readily amenable to a reduction of population density by reason of their potential for reproductive failure.

That is to say that, although the ability to reproduce may not be impaired in the individual case of any particular addict, nevertheless the addiction of itself renders successful mating less probable than for the nonaddictive person.

Our clinical experience has been that, even where successful mating does occur among addicts, the problems which cause and are a result of their habit tend to make them less able to rear their children in a socially satisfactory manner.

The children of addicted parents encounter more problems in social adjustment than most of their contemporaries, making subsequent successful mating difficult for them in their turn. Thus the potential for eventual reproductive impairment exists among addicts, even if perhaps extending over several generations.

And in this vital social function they may have replaced that pool of children who in each generation in earlier times were eliminated by childhood diseases but who are now saved by medical intervention.

(The semipermanent state of warfare which is characteristic of our species has not been an element in stabilizing populations because, until our own time, it has not reduced the female population. But in earlier times poor hygiene, productive as it was of plague diseases among adults as well as adding to the toll of child mortality, was also a factor in the automatic spacing of populations whenever they became too dense.)

The large increase in stress diseases in modern times and of stress responses including anomie, accident proneness, a possible increase in homosexuality, addiction, and so on are today probably also aspects of the operation of this group mechanism.

This bioanthropological overview of the adaptive significance of selfeliminatory behaviors places these phenomena within the framework of a context wider than that to which we are accustomed in our professional concern for the well-being of the individual.

In the process, it forces upon us the necessity of contemplating ethicomoral issues--of making a  decision as to whether our primary duty is to an individual or to our society. To offer an analogy, it is as though a surgeon were obliged to decide whether to rescue an organ to the possible detriment of the whole organism.

It is a quandary that is currently becoming apparent to widening circles of responsible scientists.

Our comparatively recent awareness of the limited nature of our biosphere and of the closely interlocked necessities both of inanimate material and of all forms of life that sustain and are sustained by it enforces a reevaluation of many, perhaps most, of our existing values.

This awareness has produced a growing number of people committed to such concerns as environmental quality, the preservation of endangered species, the control of population, the wider effects of pesticides, birth control, and so on.1

In the present-day liberal political and philosophical climate, the interest of the individual reigns supreme. The idea that a society might sacrifice certain of its individuals for the greater good of the whole is anathema, and we cannot dissociate ourselves from the reality of the prevailing morality.

We are of our times, and it is our deepest desire to improve the lot of each and every human being. This does not preclude the possibility that at some future time other moralities may supervene.

Addiction and similarly dysfunctional social behavior, then, constitute pathways along which certain individuals move toward an exit from the gene pools of their populations, and the attempt to halt their departure and to encourage them to reverse their course fosters a biological paradox .

We have seen that the phylogenetic preservation of variety within a population, whether of anatomy or behavior, does not only permit a group to survive changes in its environment. It also provides a group with a certain proportion of individuals that it may safely discard whenever its density exceeds an optimum.

Thus we recognize that those who become addictive do not have within themselves the behavioral repertoire that will enable them to move successfully into the mainstream of the life of their group.

They are, so to speak, biologically designed to fulfill a different role.

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1 We might note that, while it is reasonable to assume that conditions involving hypersensitivity to the environment may in the past have had and may yet have adaptive elements, there are genetically determined physiological variations (such as juvenile diabetes mellitus, among numerous other genetic abnormalities) that would seem to be nonadaptive in any circumstances. Such variations as these would be eliminated from a population in a natural state simply by the death before reaching reproductive age of the individuals carrying them.
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Given the orientation of our Western societies, however, we search for remedies that will allow so-afflicted individuals to live out their lives and perhaps to procreate. The heritable element of their disability may be masked through several subsequent generations, depending upon several factors, including the genetic endowment of those with whom succeeding generations mate.

It is therefore usually extremely difficult, if not impossible, to determine precisely the stage at which’maladaptive traits carried genetically are finally eliminated from the gene pool of a human population, although, by their nature, this must eventually occur if the society is to continue in existence. 

In our individual-oriented, liberal society, such a concept, however, is unacceptable. Humanitarian principles impel concerned professionals to devote all available resources to the task of rehabilitation. As humanitarians we ourselves (the authors) are also involved in such an endeavor.

As biologists, however, we have to see that a remedy for addiction does not lie in the realm of treatment for the individual but, rather, in a broader understanding of the ecological needs of the society as a whole.

Unless we see to it that steps are taken to prevent overpopulation, if not addiction then other social mechanisms will emerge that will have the effect of eliminating individuals, and a new set of problems will then have to be faced.

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Reprinted with permission from Perspectives in Biology and Medicine, Spring: 345-354. 1977. Copyright © 1977 by The University of Chicago. All rights reserved.

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From N.I.D.A. Monograph 30 - Theories on Drug Abuse: Selected Contemporary Perspectives.  [Page for pdf download, which includes diagrams and reference list.]