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No data suggest genetic dissimilarity between early human hunter-gatherers (hunter-gatherers), and evidence they are genetically homogeneous, therefore apparent differences between them can be accounted for by the effect of environment on shared genome. Human anthropology and physiology are reviewed to see if an environmental factor can be identified that could account for these differences. It is proposed that attenuated mobility with civilizations was this external factor that resulted in a sharp decline in endorphins. This explains all apparent differences between hunter-gatherers and contemporary humans. The ability of hunter-gatherers to tolerate temperature variations when unclothed and poorly sheltered and sleeping on hard and irregular surfaces is attributed to the analgesic effect of endorphins. The a mildly euphoric mood associated with ample endorphins made their life  emotionally pleasant and accounted for a high fertility rates. Physical addiction to endorphins explains the enormous work capacity of hunter-gatherers. Yet high endorphins caused by their intense mobility blocked contemplation (the ability to retain complex mental constructs), thereby obstructing technological advancement. This provides insight into contemporary health problems. Relatively low endorphin levels in contemporary humans explains the obsession with comfort through ambient temperature control and contact with yielding contact surfaces. Lacking the analgesia and euphoria of hunter gatherers, contemporary healthy humans live in pain, anxiety and depression. This contributes to  excessive medical costs and iatrogenic problems such as opioid addiction. Since sufficient endorphins production through mobility seems impossible in the present context,  contemporary humans may be well served through continual safe analgesia and anti-depressive medication to control expression to counteract an adaptation that served hunter-gatherers well but now is dysfunctional.


The notion of relative genetic homogeneity between modern man and early human hunter-gatherers (hunter-gatherers) rarely appears in scientific reports. Maybe scientists have simply accepted genetic dissimilarity based on descriptions of environmental conditions in which hunter-gatherers thrived which appear beyond the capability of contemporary humans. Possibly, the poor intellectual performance of hunter-gatherers suggests poor reasoning capacity rather than simply performance. Perhaps they were influenced by banal pseudo-scientific notions promoting genetic differences even between extant groups of humans, such as the myth of "human races." Review of the scientific literature on this subject reveals no data supporting genetic dissimilarity between hunter-gatherers and contemporary humans and strong evidence suggesting they share a near identical genome, the most convincing of which must be the sudden change from hunter-gatherer to fully modern man with the advent of civilization. This means that differences between them must be accounted for by environmental (external) factors, and understanding the environmental influence that account for differences may have bearing on contemporary human health.

From this perspective, poor contemplation in hunter-gatherers (used here to mean retaining complex mental constructs) was caused by an external factor that dulled thought processes in hunter-gatherers. Their high work capacity might be accounted for an environmental influence which compelled them to be mobile. Their attenuated discomfort from cold and high amplitude tactile loads was caused to an external influence that produced analgesia. Their ability to thrive under conditions that would cause psychological stress to modern man perhaps was caused by an external influence that made them relatively euphoric.

This report starts from the likely notion that hunter-gatherers and modern humans are genetically homologous. It searches for a single external factor that could account for all of the sudden changes that could account for the sudden transition from hunter-gatherer to modern man that occurred with civilizations.


Perhaps 250,000 years ago Homo sapiens first appeared as a distinct hominid living exclusively as nomadic hunter-gatherers in sub-Saharan Africa. There is evidence that they expanded their territory beyond this region about 70,000 years ago, but only started to cease their nomadic existence  in the last ten millennia with civilizations. They lived in groupings of about 50 individuals. Their diet was largely animal based. Large piles of smashed bones from large grazing animals have been found along with tools used to crack them. These bones were a selection of those with the thickest cortex which no animal could crush without tools, therefore hunter-gatherers were largely scavengers living off leftovers from more able predators which only humans could exploit. Bone marrow with its high content of animal based essential fatty acids is now thought to have been their staple food, with these lipids most critical to human development. Nutrition would have been plentiful when animals herds were present, but these animals migrated seasonally, therefore humans experienced seasonal hunger. Humans must have displayed group protective behavior perhaps involving weapons such as spears otherwise the predators which killed the animals from which humans scavenged bones would have chosen to feed off of humans who lacked the mobility and strength of their preferred prey.

Natural selection provided humans with low satiation, which lead to periodic obesity when nutrients were present in abundance. This is an adaptation which is present in a minority of primates all of which live under conditions of periodic (typically seasonal) nutrient scarcity. Body fat provides energy for survival. Contemporary humans possess this adaptation but in the contemporary context it results in persistent rather than periodic obesity because present day humans do not utilize energy through mobility to obtain their food, and there is no prolonged period of nutritional scarcity which eliminates excessive adiposity. In this respect it  seems inappropriate to consider obesity in present day humans as a disease, but rather a useful adaptation for survival as hunter-gatherers which has become a health concern in the current context.

Harvesting of marrow involved finding the abandoned animal carcasses, the strenuous task of separating target bones from it, which probably required tools, transporting the bones to a central location, cracking them and the extraction of marrow. All steps were energy intensive and two required prolonged mobility. Mobility is used here to signify all forms horizontal displacement of the human center of mass when weight bearing, which occurs when walking, running, and even maintaining stable equilibrium which involves constant postural adjustments therefore considerable work. When nutrients were in abundance the life of hunter-gatherers involved near constant mobility in their Sisyphean attempt to satisfy their unrelenting hunger.

Hunter-gatherers lived mainly unclothed, minimally sheltered with no evidence of sophisticated bedding, until small numbers of them eventually reached extreme latitudes.  Hunter-gatherers were far less troubled than modern man to discomfort caused by cold and high amplitude localized loading of hairy skin such as from irregular surfaces they slept on. This tolerance to environmental stress was probably not extreme enough to compromise health because humans thrived in terms of numbers. From this analysis based on genetic homogeneity, the perception of pain in contemporary humans seems far to acute excessively low because we seek greater comfort through sophisticated clothing, bedding and shoes, and pain relief though the use of analgesics, and we become addicted to opiates while seeking pain relief. . 

High infant mortality, substantial maternal mortality, predators, periodic starvation and no health care as we know it made it essential that hunter gatherers maintain near optimal reproductive rates by which every ovulating female soon became pregnant. Current low fertility rates would have been incompatible with survival of human hunter-gatherers. There is no environmental factor that has been proposed that could account for differences in fertility rates between populations, but the relation between human emotional states and fertility in humans is so strong that fertility rates can be used as a surrogate measure of the emotions of a population and vice-versa. Anxiety and depression suppress fertility whereas positive emotional states amplify it. This suggests that the mood and affect of hunter-gatherers probably was relatively euphoric despite what we would now consider harsh conditions. In contrast, the mood of present humans presently tends to be depressive, with an affect showing depression and anxiety. Perhaps global differences in mood and affect explains fertility differences between hunter-gatherers in modern humans. But environmental factor that accountable  for both mood and affect is unknown.

The is no evidence that hunter-gatherers were contemplative considering that there is no convincing example of a written language nor substantial technological innovation. This is perhaps the greatest difference between them in modern man.  The environmental factor lacking in hunter-gatherers that interfered with contemplation and present in modern man that allows it is unknown.


"Civilizations" is used here to indicate relatively large groupings of humans that live in a fixed location and use a written language. From the evolutionary perspective, the change from  humans exclusively living as hunter-gatherers to civilizations being dominant was both recent and sudden, since the earliest example that satisfies the definition civilization appeared less than 10,000 years ago, with new ones arriving periodically in various parts of the world. It is not certain what caused the transition to civilizations, but most think that the success of hunter-gatherers in mastering life in sub-Saharan Africa lead to high population density which forced hunter-gatherers to territories with limited grazing animal  populations. This forced them to experiment with vegetation to supply their nutritional needs. There is near universal agreement that agronomy, particularly the growing of grains, was the essential precondition for civilizations. Agronomy permitted acquisition of nutrients predictably with significantly less mobility when compared to hunter-gatherers.

With civilizations came almost instantly all the major behaviors and intellectual performance  of modern man. The rapidity and completeness of this transition is explained poorly by current notions of progression through natural selection. Rather, it suggests that an environmental factor caused expression of a genetic potential that was already available. Humans in civilizations near universally began wearing clothing and lived in substantive shelters, which suggests they became as sensitive to environmental variation as is modern man. Further, pain from inadequate bedding becomes a subject of the earliest writings which seems similar to current human complaints.  References appear to health concerns of sustained obesity. There is discussion of dysphoric mood and evidence of escaping it through alcohol intoxication. Perhaps most significantly, not only does contemplative powers appear, but they are substantial. There is no evidence that that the intellectual capacity of humans in even early civilizations differed from modern man and it is rare that this notion is advanced, probably because the achievements of ancient civilizations, particularly ancient Greece, seem sophisticated even by current standards. The suddenness and completeness of this change from hunter-gatherer to modern in every aspect further suggests that an environmental cause of this change.


Thorndike and Skinner identified operant conditioning as a form of learning whereby behavior is modified ("shaped") by perceived consequences of behavior ("reinforcers"), with positive and negative reinforcers either increasing or reducing the quantity of that behavior, respectively. An addictive substance is considered here to be a psychoactive chemical that is exogenous (not normally present in humans; i.e., opioids), or endogenous (normally present in humans in varying concentrations; i.e., endorphins) which are capable of producing  tolerance through repeated exposure in relatively high concentration, and a dysphoric abstinence syndrome with a sudden reduction in blood concentrations, which is a negative reinforcer which encourages continued use. Endorphin is a word that was created by combining “endogenous” and “morphine” to signify what is now a heterogenous group of psychoactive peptides produced by all humans and many other animals that are similar to morphine in that they are addictive in high blood concentration.

When endorphin blood concentration is low in humans, their affect and mood typically reveals at least modest anxiety and depressiveness without evidence of addiction. When endorphin levels are high, there is evidence of tolerance and some suggestion of a withdrawal state typical of exogenous addictive substances. Endorphins are released in humans in response to certain behaviors,,the common of which is persistent mobility of moderate intensity and well as many internal (e.g., hypoglycemia) and external stimuli (e.g., hypothermia). In healthy humans, prolonged mobility of moderate intensity is the only useful behavior available that would have been performed daily by hunter-gatherers that could produce sufficient endorphins in aggregate to create an addictive state whereby relative euphoria and analgesia, and an abstinence syndrome would be positive and negative reinforcers respectively. 


 It is proposed that change in the amplitude of mobility that occurred with civilizations caused a sharp drop in endorphins which resulted in decline  in pain threshold, loss of the euphoric mood with rise of anxiety and depression, and lower fertility which follows mood. It also allowed contemplation for the first time in humans history.

In more detail, it is hypothesized that through conditioning the endorphin system maintained an addictive state that amplified mobility of hunter-gatherers needed to provide their current nutritional requirements and adiposity to survive seasonal starvation. The positive reinforcers were a euphoric mood and elevated pain thresholds, and negative reinforcers were despotic mood, pain intolerance and an dysphoric abstinence syndrome due do endorphin withdrawal. The apparent tolerance of hunter-gatherers to cold, poor shelter and primitive bedding in actuality was an genetic adaptation that allowed safety and functionality. The present inability of contemporary humans to tolerate these conditions suggests that pain thresholds is set too low because they designed to be effective in hunter-gatherers. Hunter-gatherers likely could also maintain a mildly euphoric state despite environmental hazards and unpredictability related to minimal accumulated knowledge due to high endorphin levels. Modern man's mood and affect consists of excessive depressiveness and anxiety because we continue to be best adapted though our endorphin system to life as hunter-gatherers.

It is further proposed that the high endorphin condition of  hunter-gatherers, the euphoric mental state interfered with contemplation just as opioids attenuates contemplation in modern man. This explains the inability of hunter-gatherers to possess even the power of contemplation sufficient to even formulate a written language. The lowered endorphin levels from attenuated mobility not only ridded humans of their euphoric state but it allowed the sudden emergence of contemplation at levels consistent with contemporary man. Since their loss of their euphoric state, humans have intensely searched for an escape from their persistent dysphoria through technological innovations that make life with a low pain threshold more pleasant, and other means to escape to more natural state of euphoria though substances.


Life of the hunter-gatherer would have been pleasant in terms of  modest anxiety and physical discomfort by current standards despite unpredictability due to little accumulated knowledge and environmental stress on an unclothed body. But it also  would have been robotic by current standards with minimal intellectual curiosity nor pleasure though innovative solutions. This explains why there is no evidence that over the 250,000 years humans have existed prior to civilizations, there was never a useful written language that allowed them to accumulate knowledge, nor was there more than the most meagre advances in technology.

This suddenly began to change perhaps 6,000 years ago when some humans gave up their nomadic existence with civilizations. This sharp decline in mobility resulted  in plummeting endorphin levels. Humans were freed to contemplate for the first time in their history. Essentially the totality of human intellectual achievements and technological innovations commence at this recent point in human story. It is not certain  why civilizations came about. Most think that high densities of human hunter-gatherers in sub-Saharan Africa forced many to territories without large animal populations. Out of necessity this probably lead to attempts to use plants to supply nutritional needs. There is near universal agreement that agronomy, particularly the growing of grains was the essential precondition for civilizations.

With civilizations came diseases from large numbers of humans living in close quarters for the first time in human history. Bacteria, viruses and parasites from human-to-human transmission and through contaminated water could now decimate vast populations rather than only small numbers when humans lived in small grouping as hunter gatherers because  natural selection probably never provided them with resistance to these threats. New stresses emanated from their change in diet. Human gut anatomy, physiology and endocrine system is so poorly adapted to a diet rich in carbohydrates (and ethanol which made its presence with grain) and cellulose, consumption of these products remain a major source of ill health in contemporary humans. However the selective advantage of being intellectually unrestrained was greater than these disadvantages, and civilizations multiplied. Written language allowed the accumulation of knowledge. Bereft of high endorphins, humans experienced lower pain thresholds which required innovations such as clothing and shelter to overcome. These innovations allowed exploitation of regions in which they never could have existed previously even with the high pain threshold associated with abundant endorphins.

The change to civilizations was so rapid and recent that it may be useful to visualize contemporary humans as not fully adapted to elements of modern life because they retain essentially the body and brain of the hunter-gatherer. The relatively low and constantly declining fertility in contemporary society may be caused by by amplified anxiety and depression in due to low endorphins levels from low mobility or another adaptation that promotes mobility. Increase in mobility sufficient to raise endorphin levels to change overall emotional seems incompatible with life in a modern industrial state. Even most competitive runners would not be mobile enough.

Perhaps many current social trends, such as the non-medical use of anxiety lowering and euphoria producing drugs, and dependance on ethanol are actually a form of self-medication to escape unrelenting anxiety and depressiveness associated with low endorphin blood levels resulting from limited mobility. Modestly lowering anxiety and depression in a society may have substantial positive effects on fertility. The present low pain thresholds due to extremely low endorphins helps to explain the persistent state of discomfort in contemporary humans which has lead to obsessive searching for the "perfect" footwear, clothing and bedding, and living at narrow temperature range indoors through heating and air conditioning, and outdoors via a selection of clothes for seasonal variations in temperature.

Perhaps antidepressant medications should be in more widespread use. Antidepressant medications have been used for a half century for management of major depressive disorders. At least the current generation of these medications successfully relieve mild to moderate chronic anxiety and depression that may be below levels typically classified as a mental disorder, a condition that is so prevalent in rich countries that some have considered it universal. Antidepressants are not capable of inducing euphoria except with bipolar disorders, therefore they do not function through raising endogenous opioids. They seem to block the dysphoric state associated with low endorphin levels. They may also block somewhat the euphoric state associated with exogenous euphoria producing substances considering that many individuals addicted to these substances report less euphoria with their use.

Obesity is mistakingly considered a disease rather an adaptation necessary for survival in human hunter-gatherer humans which adversely affects health in the contemporary context. Effective and safe pharmaceutical control of appetite is needed to overcome the low satiation inherent to humans. This is currently unavailable but when it is it should be considered as a solution to adaptation that served humans well when they were hunter-gatherers but is harmful in the contemporary context.

The notion that individual fertility control through contraception would result in a more logical situation whereby those with resources to raise children who could succeed in this technological world, whereas those with no resources would reproduce less, thereby avoiding starvation, war and unemployment that has plagued the impoverished world, and individuals best adapted for success in rich countries. Rather, reproduction control programs in impoverished countries have had minimal effect of fertility, with was and starvation rampant, whereas in rich countries fertility is so low that despite increase in labor productivity, economic advancement depends on immigration of people which has some negative consequences with older inhabitants resistant to cultural practices of newcomers. If the notion of historic and current genetic homology of humans is applied to this problem, there exists environmental conditions that are present in impoverished countries that amplifies desire to reproduce and which is lacking in rich countries. Overall fertility of a population is not a logical response to economic conditions but rather it is controlled by poorly understood environmental factors, that if better understood and controllable, may benefit everyone. A similar argument can be applied to mobility, pain sensitivity, human affect and the ability to retain and manipulate mental constructs which appear to be considerably different between hunter-gatherers and contemporary humans, but are of environmental control. This report attempts to explain how environmental factors control these behaviors in humans.

It is currently fashionable to glorify human existence as hunter-gatherers. This may be appropriate considering humans are probably best adapted to this condition. They existed is relative euphoric whereas their contemporary existence entails substantial anxiety and depression. Furthermore, they existed without medications and health care which, both of which humans rely on. But adding technological advances resulting from contemplation has more than doubled the life expectancy of hunter-gatherers. They tolerated their existence through addiction to endogenous opioids which made their life extremely robotic by modern standards. Also humans seem to intrinsically enjoy creativity made possible by moderation of endorphins. If pain thresholds were elevated to more appropriate levels and depression and anxiety control inherent to modern life was made more available, few humans would turn to exogenous euphoria producing agents that have become so prevalent recently. chemicals were They were incapable of complex reasoning because of these endorphins. We now live with lower endorphins. I doubt that high endorphins is an adequate solution to the current state of low pain thresholds, anxiety and depressiveness. Human intelligence will eventually deal with the problems created by low endorphins while enjoying the use of their intellect.


It was proposed that available evidence suggests that human and hunter-gatherers share a near identical genome therefore apparent differences between them would be environmental in nature. It was proposed that a single environmental explanation that could explain all of the apparent differences between these groups is mobility amplitude. This external factor caused the changes mainly through the endorphin system. It explains the apparent differences in intellectual capacity between hunter-gatherers and modern humans. It seems to explain the apparent physical robustness of hunter-gatherers compared to contemporary man through rise in pain thresholds caused by high endorphins mainly from intense mobility. It explains their mental resiliency to what would be now intolerable by the effect of endorphins on mood. This also explains differences in fertility rates between early and current humans.