To what extent did the Neolithic Revolution cause a decline in the health of early human populations?
by Georgina Holmes
CONTENTS
ABSTRACT……………………………………………………………………….
INTRODUCTION……………………………………………………………...
DISEASE AND TRANSMISSION…………………………………………
1.1 Origins of disease
1.2 Transmission of disease within communities
1.3 Implications of disease on health
LIFESTYLE SHIFTS……..…………………………………………………..
2.1 Population growth, density and aggregation
2.1a Fertility and mortality trade-off
2.2 Sedentism, work load and physical activity
2.2a Stature, growth and body mass
2.2b Bone health and robusticity
2.3 Food Processing, food and technology
2.3a Dental health
2.3b Skull morphology
DIET AND NUTRITION…..…………………………………………………
3.1 Malnutrition & Nutritional Quality
3.1a Dietary diversity
3.1b Anaemia
CONCLUSION………………………………………………………………....
WORKS CITED……………………………………………………………….....
APPENDIX A: Source evaluation…………………………...………..
ABSTRACT
This report intends to explore the extent to which the adoption of agriculture negatively impacted the health of early human populations. Literature typically associates the transition to farming with a marked reduction in skeletal and dental health, widespread infectious disease and increased mortality rates. Rather than taking a broad generalising approach and assuming that all farming or all foraging populations are the same, this report explores the variability of subsistence methods and the lifestyle factors commonly connected to the different facets of poor health. Notably, how the varying levels of intensity of sedentism, aggregation, diet composition and domestication are more significant than the type of subsistence method in explaining patterns of health in past populations. In this report I outline why agriculture is not the sole cause of declining health and conclude that lifestyle factors play a more important role in determining whether health is adversely affected. Many of these factors are seen most commonly in farmers, largely explaining the connection between agriculture and declining health.
INTRODUCTION
It seems counter intuitive that health would decline following the adoption of agriculture. For reasons such as food security, energy-dense foods and decreased energy expenditure one could reasonably think that farmers were at a nutritional advantage. Evidence of population growth and increased life expectancy beyond the reproductive age, in turn accelerating fertility rates, seems to support this concept [1]. However, research increasingly shows health decreased following the adoption of agriculture; the prevalence of disease, physiological and nutritional stress all seem to be higher in agricultural populations [2]. Abundant skeletal remains from both hunter-gatherers and farmers show increased pathologies, bony lesions, dental and craniofacial adaptions and decreased stature and robusticity in the latter [3].
The term ‘Neolithic Revolution’ is the same as the adoption of agriculture, it does not mean that Neolithic populations are always agriculturalists. In this report, studies mentioning the Neolithic may represent either sedentary farmers or more mobile forager-farmers and the same goes for any period mentioned. All periods will be linked to the characteristics known about them from archaeological record, thus allowing conclusions to be drawn between lifestyle, subsistence methods and health, irrespective of the time period. An important note is that crop and animal domestication was a long process, intensify at different times in various regions of the world [4]. Consequently, the adoption and effects of the Neolithic Revolution span a wide period of history and arguably still continue in modern health today. Nevertheless, all studies have been critically analysed and none were found to be significantly out-dated or unreliable, with all being peer-reviewed, thoroughly researched and published in respected journals. Where an author or study may not be wholly relied upon, this will be mentioned within the report.
Subsistence methods such as agriculture are not uniform across the globe and different periods of time, with different dietary compositions and lifestyle factors which play a role [5]. Consequently, considering regional variation is of the utmost importance in understanding the impact of agriculture on health. This report considers variability in lifestyle factors, subsistence methods and the changing patterns of different facets of health.
DISEASE AND TRANSMISSION
1.1 Origins of disease
Many infectious diseases in human populations emerged during the transition to agriculture [2] [6] [7] [4] [8]. Arising mainly in the Old World – Africa, Asia and Europe – many ‘new’ infectious diseases (not found in early hunter-gatherers or non-human primates) came from domesticated animals during the Neolithic Revolution [2] [6] [9]. This evidence suggests health did decline following the adoption of agriculture.
However, it is important to note when citing Diamond’s works in the following paragraphs [2] [6] [10] that his view on agriculture is largely negative. He has previously considered agriculture ‘the worst mistake in the history of the human race’ [11] and often-times his own book ‘Guns, Germs and Steel’ (which is more of a popular science book) is used in his references. Ultimately, in rigidly viewing agriculture so negatively this overlooks a balanced view where the reality of variation can be assessed (where we see poor health in foragers, for example). Nevertheless, his academic work is peer-reviewed, researched, frequently cited, published in respected journals and an important source to take into consideration.
Domesticated animals are one of the main sources for the origins of new diseases (see Fig 1.) [4] [9] [6] due to the many ways in which zoonotic diseases can be transmitted to humans. The consumption of animal products (e.g. meat, milk); close contact with animal bodily fluids (e.g. mucus, blood, saliva); poor sanitation (e.g. animal faeces, waste accumulation, water bodies); animal vectors (e.g. mosquitoes, ticks, fleas) [7] [4] [12], are all potential vectors for the transmission of disease Moreover, domesticated animals lived close to agricultural communities; waste could accumulate nearby and the use of animals meant contact was frequent and prolonged, contact was prime cross-species transmission of pathogens [3, 13, 14, 15]. As a result, the transmission of a zoonotic pathogen to a human population is highly likely in a society which has adopted farming.
Further, the majority of diseases in temperate climates are crowd epidemic diseases. As crowd epidemic diseases require large populations to sustain the spread of the pathogen – and these numbers could not have been reached in communities until the human population grew after the Neolithic Revolution [2] [9] [6] [10] – many originated following the adoption of agriculture. Additionally, most diseases originated in the Old World, largely due to the higher number of domesticated animals that could act as vectors to pass pathogens to humans [6]. Consequently, more diseases arose in Old World agriculturalists.
These factors and opportunities for transmission are much less prevalent in dispersed and nomadic hunter-gather bands. Nevertheless, zoonoses did occur in pre-agriculturalists, the human journey exposed hominids to new animals with new parasites and infections [9]. However, pre-agricultural diseases were more likely received from animals phylogenetically close to hominids such as primates, or by consumption of hunted meat [9] [2]. Contact with other animals was not frequent or prolonged enough to make transmission of disease likely [4]. To this end, transmission of zoonotic diseases are less likely in foragers.
In some cases animals are not domesticated in the region they are used in but introduced from elsewhere [6]. This increases the likelihood of zoonotic disease transmission as pre-existing humans and animals may not have immunity to foreign zoonoses [4] [16] [10] [14]. Moreover, animals used for transport, alongside increased trade between agricultural communities, provided more opportunities for foreign pathogens to be introduced in neighbouring farming populations [4] [15]. Increased physiological stress, stunted growth and exostoses in domesticated animal remains reflects the poor living conditions of early domesticated animals [4]. This is suggestive of overcrowding, poor hygiene, nutritional deficiency and a loss of mobility – all of which provide opportunity for zoonotic diseases to be transmitted – which is strong evidence for the conditions being prime for infectious diseases in pastoral populations.
Fig 1. SOURCE: [4]
The number of diseases shared between domestic animals and humans
Whilst domesticated animals act as the vector to pass diseases on to human hosts, the domestication of crops result in host vulnerability (due to the nutritional deficiencies of a less diverse diet) [7] [4]. When an organisms cannot adapt to changes in its internal environment immunity and response is insufficient, such changes are often a result of an imbalance of external factors such as malnutrition [17]. Therefore, due to the increased malnutrition in early agricultural populations, vulnerability to infectious disease also increased suggesting the transition to agriculture made it easier for health to be affected by pathogens. Additionally, the likelihood of disease transmission rose from what it was for the hunter-gatherer to the farmer.
It must not be overlooked that non-human primates and hunter-gatherer groups were still afflicted by parasites and diseases which could be sustained in small and dispersed human populations [7] [2]. Many specific infections are inherited from early hominids and primates such as Malaria and Leprosy [9] [14]. Equally, with the journey out of Africa, hominids were exposed to environments with new microbes – new diseases arose in the early hominids, but viruses and pathogens had not evolved to be human specific [9]. Consequently, non-agricultural populations are not a model of perfect health as they are sometimes made out to be. To this end, it is the lifestyle factors which allow for diseases to originate and not the subsistence method. Although these factors tend to apply to farmers, they can also be linked to settled foragers and perhaps not applied to more dispersed/early farmers. In spite of this, the origins of many human infectious diseases stem from the Neolithic Revolution due to the lifestyle changes which make transmission more likely.
1.2 Transmission of disease within communities
The adoption of agriculture caused an increase in population numbers and density [18]. Consequently, diseases that depend on hosts or large populations in order to maintain transmission within a community increased. The aggregation of human populations increased the likelihood of transmission within human communities as contact between individuals increased; decreased sanitation and the accumulation of waste/faeces provide conditions for microbial growth; poor diet increases human susceptibility to infection; trade provided cross community transmission and crowd epidemic diseases could be sustained [4] [7] [9] [12] [3] [14] [15] [17] [19] [20] [1] [21]. Infected humans and animals sharing the same space can also spread pathogens by sneezing or coughing [4] [22] [21]. Sedentism (which is commonly associated with the agricultural lifestyle) both increases population density, and thereby contact and transmission of disease, but also means the population suffers repeated infection by the same strains of parasites (these parasites like mosquitoes become specialised to humans as there is a constant food source which allows for easy breeding and a lack of variety in species to infect) [9] and a host-pathogen relationship has time to develop and establish prolonged illness [23]. All of these papers which provide this insight are peer-reviewed, published in respected journals and not of questionable provenance, which supports the link between settlement and pathogenic transmission. Sources by Cockburn T [9] and Lallo et al. [23] do date to the 1970s, but this research still remains valid and continues to be cited, once again supporting the point.
As a result, the frequency of disease in a population increases alongside increased population numbers, settlement and density [4]. This is because there are more hosts to sustain transmission of the pathogen, thereby acting as a ‘reservoir’, and due to domesticated animals and a constant food source the vectors of disease increase [24]. This supports a connection between disease prevalence in a population and agriculture because all of these causes increase with farming more so than in foragers (even settled foragers).
Thus, settled and aggregated communities are more likely to be afflicted with diseases. These lifestyle factors will vary in different geographic regions over time, as result one subsistence method cannot be the sole cause of declining health but rather the presence of these lifestyle shifts within a population. As the sedentary and densely populated lifestyle is often associated with agriculture and the domestication of animals increased the opportunity for diseases to originate, the agricultural lifestyle is more likely to be prime for disease transmission. Namely because most hunter-gatherers are mobile, sparse and do not remain in long and frequent contact with the same animals.
1.3 Implications of disease on health
The impact of increased pathogen load with agriculture can be seen in the osteological record [23] – abundant bony lesions denote a marked decline in the health [4] [20].
Human remains show lesions from infections increased with the adoption of farming [7], for example tuberculosis (TB, from cattle) and brucellosis (from sheep/goat milk) cause bony lesions [4]. From modern day case studies, tuberculosis rarely occurs in wild animals (if it does occur they have often been exposed to captive mammals) and is associated with domestication and crowding [22]. Although early strains of TB have been identified in human evolution, [25] and neutrophilia associated with TB can survive in small populations suggesting it predates agriculture [1], the main cause of transmission is domesticated livestock (see Fig 2.) which suggests the health of early agriculturalists is more likely to be affected by TB. Consequently, tuberculosis is linked to the rise of agriculture - the abundance of bony lesions in Neolithic skeletons from around 8000 B.C. and Ancient Egyptians from around 3700 - 1000 B.C. is proof of the link between the effect of domestication on human health [22].
Fig 2. SOURCE: [6]
Zoonotic diseases which originated from domesticated animals and are now human diseases
Moreover, in Middle Mississippian agricultural samples 84% of examined bones show signs of infection compared to the earlier (and more nomadic/less crop dependent) Mississippian Accultured Late Woodland sample where only 26% of the bones contained signs of infection [23]. Although more bones were examined in the latter study – likely providing more oppourtunity for dilution of the results – more severe cases were seen in the farming sample suggesting that disease afflicted agriculturalists more than foragers. Equally, a modern study of the Agta (although a modern population their lifestyle provides insight into pre-industrialised life and so it remains a useful source) has indicated helminthic intestinal parasites increases in sedentary camps (and these are rarely seen in archaeological evidence predating the rise of agriculture), this is evidence of a greater pathogen load afflicting sedentary farmers more than foragers [1].
There is strong evidence to suggest that the Neolithic Revolution caused a substantial decline in health as a result of disease. It is clear that diseases did not just affect agricultural populations, nor did they all stem from the transition to agriculture. The types of diseases do vary between foragers and farmers; viruses with a longer latency cycle and less rapid transmission are more common in hunter-gatherers to suit the sparse and nomadic lifestyle, the opposite is true in agriculturalists [7]. Consequently, the arrival of agriculture meant pathogen-load could increase and return repeatedly. In spite of the presence of parasites and pathogens prior to the adoption of agriculture, the abundance and frequency of new diseases affecting farmers is far greater than in foragers – the Neolithic Revolution did cause a decline in human health with regards to diseases.
LIFESTYLE SHIFTS
2.1 Population growth, density and aggregation
Population numbers and density increased with agriculture, as a result of: decreased birth intervals; increased life expectancy beyond the reproductive age; increased fertility rates; a decreased energy expenditure deficit [1] [3] [17] [19] [20] [24]. This pattern of population growth appears to imply that the health status of agriculturalists improved. However, establishment of settlements, alongside increased interaction and trade with neighbours increases the opportunity for the transmission of new diseases [23]. The effect of increased disease (particularly infectious disease in dense sedentary populations) evidently results in a decline in human health and increased mortality.
2.1a Fertility and mortality trade-off
The increased fertility and population growth with the transition from foraging to farming came with a higher mortality rate trade-off [14] [1]. In a study of Agta camps by Page et al., 2016 [1], higher fertility rates were observed in the sedentary mothers. The data shows that settled mothers have a 16.7% higher Total Fertility Rate (TFR) of 7.7 than mobile mothers who had a 6.6 TFR. This can be linked to the fact that forager mothers have lower BMI scores, whereas sedentary mothers expend less energy and consume more carbohydrates. Thus, the birth interval is reduced in sedentary mothers resulting in this higher fertility rate and, by extent, a population growth.
As has been established, the benefit of growing civilisations perpetuated the transmission of disease and therefore physiological stress increases. European civilisations quickly became densely populated after the Neolithic Revolution, this was a catalyst for the transmission of diseases and decline in sanitation and they were therefore afflicted with infectious diseases [6]. In the study, large camps with low mobility were 2.8 times more likely to display lymphocytosis, with only severe eosinophilia (showing extreme helminth infestations) and highest infant mortality found in the completely settled Agta [1]. To this end, as fertility rate increases with the degree of sedentism and population growth, so does the mortality rate. This trade-off explains the contradiction between global population growth and indicates health declined and pathogen load increased with the adoption of agriculture.
Although a report on modern Agta communities, those who were in settled camps in the study had abandoned foraging for a cultivated life. Thus, the correlation observed can be applied to the Neolithic Transition and early agriculture communities due to the interplay between agriculture and sedentism. Moreover, the research is peer-reviewed, frequently cited and there are no conflicts of interest. Therefore, the study is both relevant and reliable in provenance to be used as evidence.
Furthermore, reproductive, air and water-borne diseases are easily transmitted within aggregated human populations. As an example, gut rotaviruses kill lining cells and prevent absorption and retention of fluids causing diarrhoea. With each gram of faeces containing 109 viruses, microbes could thrive in such settled and confined communities with poor sanitation – large, settled populations live amongst their waste and ill, unlike nomads [21]. As a result, the growth in the successful reproductive turnover of humans is a hotspot for diseases, this demonstrates the feedback loop of declining health with population growth in agriculturalists.
Despite mortality rates generally being high in farmers, hunter-gatherers have a low life expectancy at birth [26]. This demonstrates that prior to the adoption of agriculture the risk of death was likely to be equally high. However, the mobile nature of small foraging groups means that they are less likely to be affected by diseases and parasitic infectious as has been seen in agriculturalists. To this end, population dynamics play an important role in determining the health status of a community and while sedentism is not exclusive to farmers, and population varies regionally, the general trend is increased aggregation and a greater decline in health with farming.
2.2 Sedentism, work load and physical activity
One of the key features of the Neolithic Revolution was the change from a nomadic to a sedentary lifestyle. The shift from changing location regularly and mobile activity to staying in one location brought many causes of declining health [27] [28].
Low levels of cardiovascular disease are associated with high mobility in the Tsimane and Hadza foragers with over 135 minutes of activity per day [26]. However, modern studies do not perfectly replicate past conditions and endurance running was likely more common in ancient populations than to modern ones [26]. It is possible that prehistoric foragers were even more mobile and active than present ones, naturally this sort of evidence has not preserved distinctly in the archaeological record. Nevertheless, it offers evidence towards a mobile lifestyle being healthier.
A study by Raichlen et al. [29] suggests that hunter-gatherers are sedentary for a similar amount of time as industrialised populations, but their mode of sitting such as squatting and interrupted sitting increases muscle activity. The decrease in sustained muscle activity with the move away from foraging decreases metabolism in muscles, lipid and glucose metabolism, blood flow and worsens inflammation, many of which are factors associated with cardiovascular disease. Thus, the change in the way in which humans are sedentary is more significant than the time spent resting. Although this is early research published just this year, it provides a possible insight into how sedentism changed with agriculture and the reasons why it would cause a decline in health. Whilst this study utilises modern comparisons, it provides evidence that sedentism was not so much of a problem regarding the amount of energy expended (which would likely also hold true given the labour intensity of early farming) but the mode of energy expenditure.
Consequently, decreased physical activity and sedentism are associated with decreased health. The lifestyle shift to sedentism, and not necessarily the mode of subsistence, led to a decline in health – these lifestyle aspects will be present in forager-farmers and farmers and vary in intensity regionally. Overall, the transition to agriculture amplified these activity changes and therefore contributes to poor health.
2.2a Stature, growth and body mass
Declining stature is another possible consequence of the transition to agriculture, and it had been seen in skeletons globally and across any period where farming was adopted [30] [31].
During periods of undernourishment, stress leads to the release of catabolic hormones in order to release energy, preventing anabolic growth [32]. It has been observed in both modern and ancient studies of individuals affected by famine and malnourishment that long bone growth is retarded, which in turn leads to decreased stature [31]. Consequently, growth inhibition can also be evidence of malnutrition. Such inadequate nutrition and periods of famine may seem likely in hunter-gatherers. Contrarily, due to their dietary breadth – compared to the farming reliance on monoculture which can result in crop failures and famines – there is often a wide variety of food available to consume sufficient energy and micronutrients all year round for foragers [3]. Moreover, decreased protein consumption and early crop-based agriculture (particularly with regards to maize, wheat and rice) depletes iron abundance, resulting in anaemia and not providing adequate amino acids for growth [3] [31]. As a result, poor dietary changes are commonly associated with decreased stature. Although not exclusive to agriculture, the increased likelihood of malnutrition suggests a decline in health with farming.
It is important to note that temperature, genetics, disease and work load are also linked to changes in stature, and in some cases stature increases following the adoption of agriculture (such as in the Lower Illinois Valley [33]) [31]. A study by Macintosh A. et al. [34] found significant stature and body mass reduction in early LBK Neolithic farmers compared to preceding semi-sedentary Mesolithic hunter-gatherer-fishers, but this was then followed by recovery in later agricultural populations. These results suggest that the inclusion o