(1)
Indian Institute of Science Education and Research Pune (IISER-P), Pune, India
Abstract
Perhaps we cannot apply the hawk and dove model of animal behavior and its implications to endocrinology and metabolism to humans as it is. There have been a few attempts to apply these concepts to humans, but there are some problems with this approach. Sapolsky [1] thinks that socioeconomic status (SES) in humans is comparable to social dominance and subordination in animals, and therefore, lower socioeconomic strata suffer from the same health problems as low-ranking primates. There are many problems with the argument. First of all, Sapolsky himself shows that not in all animal species low social rank is associated with high corticosteroids, which is said to be one of the markers of stress-related health problems. The negative association appears to be certainly true for species in which physical strength and aggression are the most important determinants of social rank but not necessarily so in other species. In orangutans, for example, there is a clear developmental and morphometric distinction between the dominant and subordinate males. The subordinate males are “arrested” in a juvenile-like morph, although they are sexually mature. These subordinate males are aggressive and often coercively mate with females. Here, we see that unlike most other species, subordinate males do not have higher glucocorticoid levels [1–6]. This may be because glucocorticoids have a stronger negative association with aggression than with social status. Orangutans are an ideal example where there is sufficient evidence to show that “dominant” and “subordinate” are actually two distinct mating strategies of males. Here the subordinates show aggressive behavior towards females, and their corticoid levels appear to be determined by aggression rather than subordination. Therefore it appears to be not the dominance hierarchy itself but the ways of attaining it and its behavioral consequences that decide the physiological correlates. In modern human society, physical aggression is not the predominant means of attaining high socioeconomic status (SES), and therefore, SES in humans may not be equivalent to social dominance hierarchy in animals as Sapolsky claims. The other reason to doubt Sapolsky’s claim is that human data all over the world does not show the same trends across socioeconomic groups. Sapolsky refers to the picture in America where obesity and metabolic syndrome are claimed to be more prevalent in the lower socioeconomic class. But that is not necessarily the case across the globe and at all times. Even within the USA, studies addressing this question are not equivocal [7, 8]. In South Asia and Africa, T2D and CVD have been disorders of the affluent so far [9–12], although the prevalence might be rapidly increasing in lower strata recently. The third reason to doubt Sapolsky’s conclusion is that although there is no doubt that humans evolved from animals, human evolution has taken a somewhat different line with respect to cognitive, emotional, and social aspects of life. It is possible therefore that some of the concepts that we discussed in the last chapter apply to humans but others do not. Much careful reexamination of these concepts is therefore needed before we can make any inferences about behavior and physiology of humans.
Perhaps we cannot apply the hawk and dove model of animal behavior and its implications to endocrinology and metabolism to humans as it is. There have been a few attempts to apply these concepts to humans, but there are some problems with this approach. Sapolsky [1] thinks that socioeconomic status (SES) in humans is comparable to social dominance and subordination in animals, and therefore, lower socioeconomic strata suffer from the same health problems as low-ranking primates. There are many problems with the argument. First of all, Sapolsky himself shows that not in all animal species low social rank is associated with high corticosteroids, which is said to be one of the markers of stress-related health problems. The negative association appears to be certainly true for species in which physical strength and aggression are the most important determinants of social rank but not necessarily so in other species. In orangutans, for example, there is a clear developmental and morphometric distinction between the dominant and subordinate males. The subordinate males are “arrested” in a juvenile-like morph, although they are sexually mature. These subordinate males are aggressive and often coercively mate with females. Here, we see that unlike most other species, subordinate males do not have higher glucocorticoid levels [1–6]. This may be because glucocorticoids have a stronger negative association with aggression than with social status. Orangutans are an ideal example where there is sufficient evidence to show that “dominant” and “subordinate” are actually two distinct mating strategies of males. Here the subordinates show aggressive behavior towards females, and their corticoid levels appear to be determined by aggression rather than subordination. Therefore it appears to be not the dominance hierarchy itself but the ways of attaining it and its behavioral consequences that decide the physiological correlates. In modern human society, physical aggression is not the predominant means of attaining high socioeconomic status (SES), and therefore, SES in humans may not be equivalent to social dominance hierarchy in animals as Sapolsky claims. The other reason to doubt Sapolsky’s claim is that human data all over the world does not show the same trends across socioeconomic groups. Sapolsky refers to the picture in America where obesity and metabolic syndrome are claimed to be more prevalent in the lower socioeconomic class. But that is not necessarily the case across the globe and at all times. Even within the USA, studies addressing this question are not equivocal [7, 8]. In South Asia and Africa, T2D and CVD have been disorders of the affluent so far [9–12], although the prevalence might be rapidly increasing in lower strata recently. The third reason to doubt Sapolsky’s conclusion is that although there is no doubt that humans evolved from animals, human evolution has taken a somewhat different line with respect to cognitive, emotional, and social aspects of life. It is possible therefore that some of the concepts that we discussed in the last chapter apply to humans but others do not. Much careful reexamination of these concepts is therefore needed before we can make any inferences about behavior and physiology of humans.
One obvious common element is that net reproductive success has played a major role in the evolution of both. The mating systems however are considerably different. A “marriage” system appears to have taken root and became almost universal in the human race. Although the details of the form of marriage are quite variable, long-term commitment and investment in child care by both genders are a common norm in marriages. Marriages do not guarantee faithful monogamy, but still monogamy appears to be a modal picture in the human mating system. This is certainly different from the closely related chimpanzees but not unique to humans. Lifelong monogamous pairing is common in some large birds like eagles or cranes. Human males do not have individual territories as in many animals, but some parallels to territoriality in the form of ownership of land or monopoly over a business niche do exist. Also in the strict sense there are no alpha males but a parallel concept of group leaders does exist.
The comparison most relevant to us is in the nature, form, and role of aggression and dominance hierarchy. Here there are substantial differences. In animals although there is substantial variation across species in the nature and form of aggression, escalation, and risk of injury, aggression is primarily physical. Nonphysical aggression, such as threat displays without physical attack, most commonly involves displaying strength or potentially harmful weapons such as canines. It is difficult to find any example where an animal can successfully establish dominance without being physically capable. This can happen in humans. Some anthropologists have differentiated between “dominance” and “prestige,” both independently contributing to Darwinian fitness to a similar extent [13]. They define dominance as a superior ability to inflict costs on others and prestige as an individual’s relative ability to confer benefits on others. This means that high status in humans can have more than one alternative meaning.
Unlike most animal species physical strength and aggression are only one of the several paths of achieving social status in humans. Apart from physical aggression, there are two other forms of aggression in humans which are either absent or of relatively minor importance in animals. One is verbal aggression that consists of verbally abusing, insulting, psychologically hurting, or threatening someone. The other is political aggression where the aggressor needs to neither inflict physical injuries nor use abusive words or harsh tone towards the victim. He may even talk with very pleasing words but at the same time manipulate circumstances and other individuals to cause injury to the victim. Apart from aggression, high social status can be achieved in humans by altruism, making alliances, or other types of skillful social manipulations. Obviously since the mechanisms and energetics of the alternative means of gaining hierarchical position are different, the physiological needs are also expected to be very different, and we cannot expect to see the same physiological parameters associating with high socioeconomic status irrespective of the means of achieving it.
We categorized animal behavior into hawk and dove strategies based on the aggressive nonaggressive dichotomy. We will not be able to do so in humans unless we segregate the different types of aggressions. We therefore prefer to substitute the terms hawk versus dove with “soldier” or “warrior” versus “diplomat” when it comes to humans. This distinction is not based on the presence and absence of aggression but rather on the nature of expression of aggression. It is also not based on SES but on the means of achieving SES. Physical aggression is a characteristic of a soldier, whereas verbal and political aggression or other nonaggressive means of gaining social position that of a diplomat. The words “soldier” and “diplomat” certainly do not refer to the profession; they rather refer to personalities, behavior, and physiological makeups of individuals. Our classification of soldier and diplomat is different from the dominance–prestige dichotomy of von Rueden et al. [13]. Soldier–diplomat is in a different dimension, and both dominance and prestige can be attained by either soldier or diplomat means. Since the physiological requirements of a warrior are similar to that of a hawk, we expect that the physiological correlates of a hawk should be seen in a soldier and that of a dove in a diplomat. We would expect therefore that soldier personalities would typically have high sex hormone levels, low serotonergic activity, low levels of cholesterol, corticosteroids and insulin in plasma, and higher insulin sensitivity. A diplomat personality, on the other hand, would be low in sex hormones with higher serotonergic activity and has higher plasma cholesterol, cortisol, insulin, and insulin resistance.
The transition from hawk–dove to soldier–diplomat has important consequences. The availability and security of food are lower for the lower ranks in primates as well as in humans. In an animal society physically weaker individual is most likely to have a lower calorie intake than stronger individuals. If a weaker individual finds a source of rich food, there is a high probability of a dominant individual snatching it. The dominant individual would be less interested in snatching less-rich food. Therefore it would be normal for a weaker individual to have a higher proportion of fiber-rich and calorie-poor foods, and evolution might have fine-tuned a physiological link between subordinate status and fiber-rich diet. The physiology of a subordinate or nonaggressive individual might be optimized for a high-fiber low-calorie food. Physically weak individuals having high access to calorie-rich food with substantial food security is perhaps unique to human societies, that too specifically modern human societies. Perhaps in the hunter-gatherer stage, physical strength and fitness would still have been one of the major factors contributing to social dominance and access to food and other resources. Even in agricultural societies, physical strength and activity would be important in deciding productivity and therefore access to food of an individual. But this relation is lost in modern urban life. With the rapid development of civilizations over a relatively brief period, human social structure changed rapidly, and the relevance of physical strength and aggression to social dominance and food security went on decreasing monotonically. This would doubtlessly have physiological consequences that are unique to the modern human society. The period over which the social change took place has been too small for evolution to bring about major changes in human biology. Therefore it is likely that we retain many of the ancestral responses. For example, a subordinate animal that has lower food security would be benefited by binge eating since food once eaten cannot be snatched by another dominant individual. Hyperphagia after social defeat or subordination has indeed been shown in many experiments [14–18]. Glucocorticoid levels that are typically higher in subordinates increase food intake [19]. This tendency which was once adaptive is perhaps still retained by us in spite of changed social structure. Many studies have indicated that social subordination is one of the important factors associated with eating disorders [20, 21], obesity, and T2D [22, 23] in humans too.
This raises a possibility that is speculative at present but appears logical and therefore needs to be pursued seriously. Since weaker individuals in nature are more likely to have lower calorie intake and higher fiber content in food, we would expect some physiological fine-tuning done by evolution to optimize this kind of a diet in physically weaker individuals. If a weak individual eats high-calorie and low-fiber food, there is a mismatch with the evolved tendency which might show up in the form of some pathophysiological processes. On the other hand individuals who are physically strong and have a rough and tough life may consume high-fat high-calorie food without showing any signs of adverse effects as their physiologies would be programmed for this kind of food. If this hypothesis is correct, diet-induced insulin resistance should be seen only in the diplomat class of people and not in the soldier class. This is perhaps what we see in the Masai tribe that consumes a diet rich in animal fat but remain insulin sensitive and hypocholesterolemic [24–27] or in endurance athletes that have high IMTG and are still insulin sensitive [28]. It is likely therefore that a combination of behavioral strategies and diet is what matters and not diet alone.
A good metaphor for the observed effects and importance of diet in the development of metabolic syndrome is that of sugar intake in diabetes or salt intake in hypertension. A large variation in sugar intake is easily tolerated by a nondiabetic individual without losing control of blood sugar, but for a diabetic person, even a moderate intake of sugar may shoot up plasma sugar levels much beyond the normal range. Similarly high-fat diet causes no detectable problem for a warrior, but for a supernormal diplomat, it can lead to signs of obesity and metabolic syndrome in no time. Here lies a possible answer to the diet paradox described in Chap. 3. Across the globe there are many tribes that traditionally live on extremely fat-rich or carbohydrate-rich diets and still show no signs of obesity, hypercholesterolemia, and insulin resistance, whereas a smaller rise in dietary fat or soluble carbohydrates in the modern society is evidently associated with obesity and related disorders. As long as the behavioral components of a hunter–gatherer–warrior lifestyle are intact, dietary macronutrient composition is likely to be of minor importance. Once the deficiency of these behaviors develops, diet suddenly becomes important. It is important to realize that majority of research on diet-induced obesity has been done in the modern urban or semiurban society. Animal research is typically on caged rats. Imagine a hypothetical researcher living in a society made up only of untreated diabetics. This researcher is studying the effect of dietary sugar intake on plasma sugar. Since this person has never examined normal healthy individuals, he will not realize that there is a narrow range of normal glucose levels which is not affected by consuming more or less sugar on a given day. Similarly, a diet school researcher who has never performed his diet experiments in hunter-gatherer societies (without changing their normal behavior) will never realize that macronutrient composition has little to do with body composition and metabolic alterations typical of metabolic syndrome.
The current status of diet-induced obesity in humans is an effect of drifting from hawk–dove to warrior–diplomat. In nature dove would develop thrift but is unlikely to become obese since it is unlikely to have higher access to calorie-rich food. The diplomat has a physiological makeup of a dove but still has higher access to calorie-rich food which might be a root of the problem. Hawks or warriors, on the other hand, may not worry about calories and are unlikely to develop obesity and insulin resistance in spite of having calorie-rich food. Their endocrine and behavioral makeup will convert the extra energy into muscle protein and become stronger than becoming obese. We are developing a hypothesis now that the warrior–diplomat dichotomy is one of the major drivers of physiological state. The deficiency of soldier behavior and perhaps a supernormal diplomat behavior drives neuroendocrine and metabolic changes leading to increased susceptibility to diet-induced metabolic syndrome. But before developing the hypothesis further, we need to be careful about defining the warrior/soldier versus diplomat dichotomy.
What Characterizes Soldiers and Diplomats
Table 6.1 summarizes the postulated differences between soldier and diplomat behaviors which can be easily compared with Table 5.1. The importance of physical activity in controlling obesity and insulin resistance is well accepted by current thinking. But in the current thinking, the importance of physical activity is for burning calories. As I will argue eventually the difference between soldier and diplomat is far beyond the rate of calorie burning. All other elements of the dichotomy listed in the table are absent in the current thinking, and there are reasons to think that they are more important than calorie burning alone as we will see elaborately one by one.
Table 6.1
Typical characteristics of soldiers and diplomats
Soldier/warrior | Diplomat |
|---|---|
Physically active | Relatively sedentary |
Muscular and strong | Physically weak |
Physically aggressive, often proactive | Avoider of physical aggression (other forms of aggression may be seen) |
Swift, agile, active complex NMCs | Slower reflexes |
Risk taker, exploratory, and adventurous | Risk and adventure avoider |
Injury prone | Less injury prone, active harm avoider |
Tolerant to physical injuries and discomfort | Lower tolerance to injuries and discomfort |
Higher spatial skills and memory | Higher verbal memory and cognitive skills |
Socially simple | Socially smart, manipulative, having higher levels of political skills, tactical deception |
Since the warrior–diplomat dichotomy is primarily (but not exclusively) based on physical aggression, we should start by defining physical aggression in the context of human behavior–physiology interface. This is extremely important since the word aggression has been used in a variety of contexts and with an equally wide variety of connotations. Even the treatment of diabetes is often called aggressive when it intends to control the sugar very tightly by all possible means. In the social context aggression often has a negative connotation and has been commonly viewed in psychiatry as a pathological behavior.
I will refer to physical aggression here as all the neuromotor acts involved in Stone Age hunting and fighting. These acts include hitting, throwing with aim, punching, kicking, chasing, grabbing, dodging, escaping, etc. Aggression is not anger, irritability, or hostility. Although anger may provoke aggression, anger is not aggression itself. There can be anger without physical aggression and aggression without anger. A carnivore chases and kills a prey not because it is angry on the prey, but it is an act of aggression natural for a carnivore. The same is true for irritability and hostility which may provoke aggression at times but are not identical with aggression. I will use the term aggression independent of its intentions and values such as good or evil. Aggression need not always be antisocial and therefore need not be viewed as bad all the time. In fact for maintenance of peace, law, and order, some amount of aggression needs to be used which can be viewed as good or prosocial aggression. I will use the term aggression to reflect the neuronal, endocrine, and metabolic mechanisms that are involved in Stone Age physical aggression independent of the social and moral context of it. For convenience and clarity, whenever there is a reference to verbal or political aggression, it will be specifically called verbal or political aggression or a more inclusive term—diplomat aggression. When used simply as aggression in this book, the default meaning would be physical aggression.
Aggression is also not equivalent to violence. Modern violence with remotely controlled bombs, missiles, and machine guns need not involve aggression by our definition. Pulling the trigger of a revolver or pressing a button of a remote control may not be recognized as an aggressive neuromuscular act by our Stone Age bodies. On the other hand digging to plant a tree is not a violent act, but it is physiologically aggressive as it involves muscle activity similar to what our Stone Age ancestors used in hunting. In fact digging itself was a common activity in hunting of burrowing animals. But this does not mean any muscle activity is aggressive. The act of walking on a treadmill, for example, does use muscle and burn some calories but has a small, if any, component of aggression.
It is this aggression that I consider one of the most important criteria to distinguish a soldier from a diplomat. Soldiers use physical aggression whereas diplomats avoid it although they may use nonphysical forms of aggression. Is the soldier–diplomat dichotomy an artifact of modern civilization or did it exist from the Stone Age? The latter appears to be more likely since it is a continued and gradual transformation of hawk–dove dichotomy of animal life. There is some evidence that even in human societies, the contribution of physical aggression to reproductive success is negatively frequency dependent as with the hawk and dove model. A comparative study of aggression in two tribes showed that reproductive success of aggressive individuals was greater than submissive ones in the Yanomamo societies but was lower in the Waorani tribe where the frequency of aggressive encounters was much higher [29]. This suggests a negative frequency dependence of reproductive success contribution of aggression. Negative frequency-dependent selection is known to operate in human social systems [30]. Accordingly similar to hawk and dove, soldier–diplomats are likely to have negative frequency dependence and therefore would coexist in a society. The equilibrium proportion of soldier–diplomats would depend on their payoffs that change with the nature of the societal structure. Today’s hunter-gatherer societies almost invariably have more or less specialized shamans or magic men who perhaps do less of hunting-gathering themselves but make living by creating, propagating, and exploiting a belief system. Shamans can be viewed as the ancestral diplomats of human civilization. More diplomat niches grew with the gradual transitions into agricultural, urban, industrial, and information-based societies. Throughout this transition the proportion of diplomats has grown monotonically. Nevertheless even in today’s diplomat-dominated societies, soldiers do exist in both pro- and antisocial roles.
Having defined aggression, we also need to worry about the conditions under which physical aggression can be adaptive and conditions under which it is maladaptive. Since both the costs and benefits of physical aggression are potentially very large, very subtle mechanisms must have evolved to fine-tune expression versus suppression of aggression and accordingly mobilizing the neuroendocrine and metabolic machinery in support. Since suppression of aggression is particularly important for insulin resistance, we need to look at the conditions for aggression suppression in sufficient details.
When to Express and When to Suppress Aggression
Food and sex are the two major natural causes of aggression in an evolutionary context. Other causes such as territoriality, social ranking, self defense, mate guarding, and maternal aggression are all related to the two basic needs of food and reproduction. In modern life the nature and purpose of aggression may have changed substantially, but the behavior–physiology links have evolved for the Stone Age, and therefore, we need to think of the Stone Age causes of aggression, expression, and suppression. Effective aggression can result into more access to food or better mating opportunities. However, aggression has an energetic cost as well as increased risk of getting injured. Therefore when there is no need for aggression or aggression is unlikely to be effective, it needs to be controlled to avoid unnecessary risk of injuries. Some commonly occurring conditions when aggression needs to be suppressed are:
1.
Full meal: A satiated individual does not need to be aggressive and therefore cues of food satiety such as physically having a stomach full, high plasma glucose, or raised insulin levels signal aggression control. This is achieved centrally by stimulating brain serotonin [31, 32]. The role of serotonin in aggression suppression is well known [33–38]. Therefore it is not a coincidence that serotonin and insulin happen to be food satiety signals and simultaneously aggression suppression signals. It is adaptive to suppress aggression after having food, and serotonin serves as the main bridge linking the two.
2.
Stored fat: Energy reserve in the form of fat should also signal aggression control since there is little desperation for food. If energy stores are exhausted, the individual has more desperation for food which increases risk-taking behavior and thereby readiness to engage in an aggressive encounter, particularly one related to competition over a food resource. This appears to happen by a number of mechanisms. Higher levels of FFAs facilitate cholesterol synthesis, and cholesterol suppresses aggression by stimulating serotonergic signaling [39–44]. Alternatively leptin also might have aggression suppression effects through activation of POMC neurons [45]. Obesity is also associated with hyperinsulinemia, and insulin has effects on the brain serotonin level which appears to be antagonizing aggression as stated above. High-fat intake has also been shown to reduce aggression in humans and other primates [44, 46, 47].
3.
Loss of sexual desire/function: The effects of sexual satiety should be similar to food satiety since sex is an equally strong motivating factor for aggression. Interestingly, the mechanisms by which sexual satiety reduces aggression are also similar to those of food satiety and involve serotonin signaling [48, 49]. Apart from sexual satiety, castration or loss of sexual motivation for any other reason should have an aggression suppression effect too. On the other hand, loss of aggression, dominance, or physical strength should downregulate sexual desire as well. This is because the opportunities and freedom of sex of an individual is much restrained in the presence of a stronger same-sex rival. Engaging in sexual activity in the presence of a stronger rival is inviting attack and injury, and therefore, both sex and aggression should be corepressed by a perception of being subordinate to someone of the same sex. Interestingly in movies, almost all over the world, sex and violence frequently go hand in hand. This association has a possible biological basis. The endocrine as well as neuronal mechanisms involved in the two have a large overlap.
4.
Being weaker than the opponent: It makes no sense to initiate aggression when the rival is stronger. Therefore weaker individuals should shun aggression. For this to work, there should be a mechanism to judge one’s own strength vis-a-vis that of the other. This is not an easy task. Since any individual cannot see its own size and that of others from the same perspective, a comparison is difficult. Nevertheless since this judgment could be very crucial for survival and reproductive success, elaborate algorithms are likely to have evolved taking data from a variety of sources. Mock fight is a known mechanism; eavesdropping on others’ conflicts can give useful data which may be stored in memory and retrieved in the face of a conflict. However, history is not always reliable since relative strengths of individuals are dynamic. There ought to be mechanisms to sense one’s own muscle power and continually update these data. This could be done through the sensory nerve endings in muscle. Muscles are known to be rich in sensory nerves. The function of these nerves could not be restricted to muscular pain. The sensory nerves are shown to fire at every contraction of the muscle, but why these signals are generated and what happens to these signals are not clearly known. I think that these signals are extremely important to continuously sense and update a judgment of one’s own muscle power which is crucial in making decisions as to when to initiate and when to suppress aggression. A common experience is that when muscles are temporarily weak owing to sickness of any kind, we “feel” the weakness. This self-appraisal might be extremely important in deciding behavioral strategies. I expect therefore that a “feeling” of strong muscle should have a proaggression effect, and a feeling of weakness or fatigue would be anti-aggression factors.
5.
Crowding: Although it may sound counterintuitive, crowding suppresses aggression. This argument is very well supported by theory as well as evidence over a wide variety of species. We will look at this much more elaborately in a separate chapter.
6.
Mechanistic checkpoint: Before beginning aggression it is necessary to check that all the machinery needed for initiating and executing aggression and coping with the possible consequences is in good condition. Initiation of an act without being prepared for the requirements for execution and coping with possible consequences is an indicator of a badly designed system. Since aggression is an important determinant in evolutionary fitness, evolution would certainly have built in this checkpoint before beginning aggression. Although the concept of aggression checkpoint is new, it is easily testable. A testable prediction would be that any defect or deficiency in factors that build and strengthen bone and muscle such as vitamin D should have anti-aggression effects. Similarly factors arresting or limiting muscle strength such as myostatin should also arrest aggression. Any defect in vascular contraction–relaxation mechanisms should also suppress aggression since blood flow control is critical in regulating blood supply to muscle as well as arresting bleeding in case of an injury.
Since we are considering the argument that aggression suppression is the main factor linking behavior and lifestyle to metabolic syndrome, we should expect all the ecological and social factors suppressing aggression to be obesogenic and/or diabetogenic. Overeating, stored fat, sexual dysfunction, physical weakness, social subordination, and exposure to crowding should all have significant associations with metabolic syndrome, and we should be able to assign a causative role to them. Much of this is certainly testable, and there is evidence for many in already-published literature as we will eventually see.
Some of the above conditions of aggression suppression work at acute and others at chronic level. For example a full meal should lead to short-term aggression suppression, but stored fat should show a long-term effect. Particularly interesting case is that of muscle weakness. Transient weakness owing to exhaustion or damage is also a disadvantage in an aggressive encounter, and therefore, aggression should be suppressed. Interestingly such short-term effects on muscle have been shown to induce transient insulin resistance. Although exercise is well known to increase insulin sensitivity, muscle exhaustion after marathon running is accompanied by short-term insulin resistance [50]. Eccentric exercises or any other exercises that cause muscle damage or soreness also increase insulin resistance which is not restricted to the damaged muscle [51–57]. This is difficult to explain by the lipid centric theory. In marathon running or any other intensive exercise, substantial fat is burnt, and therefore, insulin resistance should reduce. But damage or exhaustion increases it. Any major debilitating injury [58], burn [59–61], acute infections or sepsis [62–64], acute pain [65], or surgery [66–68] induce transient insulin resistance. In brief, a body condition that induced weakness and thereby transiently makes aggression impossible or unprofitable is bound to induce insulin resistance. This illustrates the tight association of loss of aggression with insulin resistance. Even short-term loss of aggression leads to short-term insulin resistance. Such short-term insulin resistance is unlikely to have any clinical importance. Nevertheless, for us, it is an important demonstration of the more or less obligate association between loss of aggression and insulin resistance. Chronic muscle weakness, on the other hand, is expected to result into chronic loss of aggression and with accompanying long-term insulin resistance. This is certainly likely to have clinical implications.
Apart from aggression there are other characteristics that differentiate soldiers from diplomats. Following Table 6.1 we can make a number of predictions. (1) The first very obvious requirement is strong bone and muscle without which soldier behavior would be counterproductive. It is indeed true that insulin resistance is associated with weak muscle [69–72]. (2) Soldiers need to have quick reflex reactions and agility which the diplomats may afford to lose. Therefore we may expect that insulin resistance may be associated with loss of quick reflex actions. (3) Soldiers need high-level spatial skills since a chase in a forest involves fast running on an unpredictable trajectory, and then it is equally necessary to find the path back. Those who experienced getting lost in a forest will understand the importance of it. Forest-living tribes have an amazing ability of mental mapping and reorientation which urban dwellers find difficult to achieve even with the help of devices such as a magnetic compass and GPS. Diplomats on the other hand need to have better social manipulation skills, facial recognition, and face reading. They need to be better at verbal memory, although they may compromise on spatial memory. (4) Soldiers also need to have a higher tolerance to physical discomfort such as pain from minor injuries, natural fluctuations in temperature, or variation in feeding intervals. (5) Soldiers are more prone to physical injuries, and their immune system needs to be geared up to take care of wounds. Diplomats can avoid physical injuries to a large extent, but if they are in a more social and perhaps enclosed indoor environment, they may be exposed more to respiratory infections. Therefore the behavior of the immune systems of both could subtly differ. (6) It is well known that people are able to solve mathematical problems more easily if presented in an appropriate context than in an abstract form [73]. My speculation is that the context in which soldiers and diplomats would do better mathematics should be detectably different. A soldier should be able to predict the trajectory of a fast-moving object and act accordingly to catch or dodge it within a fraction of a second without understanding the mathematics behind it at a conscious level. A diplomat on the other hand may solve an equally mathematically intricate problem in a social context without understanding the underlying mathematics. In a most likely case they would both fail in each other’s mathematical tasks. It can be clear from this discussion that our hypothesis is testable by means of a large number of testable predictions. Many of them are already substantially supported as we will see later. The important point to be illustrated now is that the facets of soldier–diplomat dichotomy other than physical activity can be tested, and these can really differentiate between the older way of thinking which has already recognized the importance of physical activity and the new thinking that has many more components in addition to physical activity.
A soldier or diplomat behavior is highly contextual. Both personality and the nature of challenge decide whether the response to the challenge will be a soldier or a diplomat behavior. Different individuals can give different responses to a given challenge, and this depends predominantly on their personalities particularly in the context of social challenges. However certain types of challenges do not give much choice and compel the responder to behave like a soldier or like a diplomat. The two are also not completely independent, and the nature of challenges faced in the past influences personality at least partially. Genetics certainly plays some role in deciding personality, although currently we do not know to what extent. The terms soldier–diplomat therefore do not simply reflect genetic predispositions or environmental influences alone but are a complex outcome from genetic, developmental, social, environmental, and stochastic elements.
So far I have introduced the concept of hawk–dove or soldier–diplomat as if they are mutually exclusive and strictly dichotomous. In reality as well as in theory, they need not be. I did so for the convenience of description. They should rather be viewed as two ends of a continuum, but a dichotomy is an easier way of expression while introducing a concept. However if we recall the original hawk and dove model, there are two possible solutions which are mathematically equivalent. Either there could be a population equilibrium consisting of an optimum proportion of pure hawks and pure doves or there can be a mixed strategy ESS. The mixed strategy ESS implies that the same individual can behave as a hawk sometime and a dove at other times. Similarly we can think of a mixed soldier and diplomat personality or of soldier and diplomats as two components of personality in a state of balance. There are different physiological requirements of the two components. However the body has sufficient flexibility to give the appropriate response to appropriate behavior. Such flexibility in the physiological responses is quite well known. Problem may arise if this balance is lost.
I am going to argue and demonstrate henceforth through several chapters that it is the lost balance between warrior–diplomat components of personality in the modern urban human behavior that has given rise to the epidemic of obesity and type 2 diabetes. For a person with a moderate mix of soldier and diplomat elements, both the associated physiological responses are adaptive and flexible. The adaptive responses become pathological only after losing the balance and going to the extremes of behavior, in this case giving up soldier behavior almost completely and adopting supernormal diplomat behavior. Steven Pinker [74] has shown that violence has been decreasing in human history, and I think, as compared to violence, physical aggression has decreased orders of magnitude more dramatically. Most of the violence today is mediated more by technology and less by physical aggression. It is quite likely that this is one of the factors behind the epidemic of obesity and metabolic syndrome. In order to understand the pathological consequences of the supernormal diplomat behavior of the modern human society, we need to understand why the endocrine and physiological correlates of diplomat are adaptive for diplomat behavior first. Then it would be easy to extrapolate and see how they turn pathological if stretched beyond the limit in which they evolved.
Much of the logic of these arguments remains the same as that in the last chapter, but we will see now what modifications may be necessary while applying it to humans. Insulin resistance changes the energy budget allocation on adopting a predominantly diplomat lifestyle. This principle is applicable to animals as well as humans, but the change is of a higher order of magnitude in humans. Human brains are much larger, their energetic requirement is substantial, and the contribution of cognitive activities to success is considerably larger in humans. Therefore, in humans, it makes a great sense to finely regulate the brain glucose supply according to the need and insulin action, and insulin resistance is one of the mechanisms of regulating brain glucose supply. The tendency to develop insulin resistance in humans on adopting a diplomat life is expected to be quantitatively much sharper than other primates although qualitatively in the same direction.
Of particular importance is the direct role of insulin in the human brain. Early studies on glucose metabolism in the brain indicated that the uptake of glucose in the brain is independent of insulin, and therefore for several decades, insulin was not perceived as important to brain activities. However insulin receptors are widely distributed in the brain indicating that insulin has some other function in the brain. The role of insulin and its receptors in the cognitive brain functions such as learning and memory has been demonstrated independently by many research groups in animal as well as human system [75–80]. What is of greater interest but unfortunately with scanty research inputs is the specific effects of insulin on mood, emotions, and behavior. Kern et al. [77] studied the effects of insulin on preattentive sensory processing (i.e., before the stimulus gains access to working memory) versus attentive processing (i.e., relatively delayed processing after the stimulus enters working memory, which involves meaning and significance attached by the subject) and demonstrated that insulin impaired information processing at preattentive level but enhanced the slower attentive processing. This might be of great relevance to the soldier–diplomat behavioral axis since hunting or fighting involves a greater component of preattentive processing, and diplomat activities may need more of attentive processing in the hippocampal and frontocortical areas. Insulin infusion also affected mood. The high-insulin infusion group experienced reduced restlessness and annoyance and had less difficulty in thinking [77]. Unfortunately, no more research is found in published literature addressing this aspect of insulin action. But we can make a more generalized testable prediction here that if insulin is infused while keeping glucose levels constant, one should see impairment of soldier-related characteristics such as quick nerve–muscle coordination actions, physical risk-taking, aggression, and tolerance towards physical pain and discomfort. On the other hand one should see simultaneous enhancement of tasks involving memory, thinking, and problem solving in a social context. Such experiments will be of great help in resolving between the two alternative interpretations of insulin resistance syndrome. Currently only the Kern et al. [77] results appear to be the ones available in literature, and they are in support of our expectation that high levels of insulin suppress certain components of soldier behavior and enhance certain components of diplomat behavior.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
