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Plant energy

All activity is powered by energy and the entire community of life is powered by the Sun’s energy stored in plant tissues. This energy is absorbed into other bodies when plant tissue is eaten – sometimes indirectly as meat which is itself plant-derived.

Humans, like other animals, are totally dependent on plants, so it is hardly surprising that acquiring plant food-energy has played a crucial role in human history while the use of the concentrated plant energy stored in fossil fuels created modern globalized industrial and post-industrial society. 

Baron von Mueller

The Sun

Ultimate source of the plant energy that powers the entire community of life

The Sun is 4.5 billion years old.
The temperature in the core (a hot, dense plasma of ions and electrons) is 15 million degrees celsius, generated by nuclear fusion.
It takes just over 8 minutes for the Sun’s light to reach Earth
Sun-worship makes a lot of sense
Courtesy Wikimedia Commons – Kelvinsong – Accessed 17 September 2018


All activity uses energy.  Historically we can regard energy as the ultimate means for ‘getting things done’.

Plants get their energy from the Sun and humans (until the recent advent of solar, wind, hydro, and nuclear) used the energy of plants for both individual and collective development.

Human history may be divided into three major phases, each powered by the Sun’s energy stored in plant chemicals during photosynthesis. These three phases we can call natura, agraria, and industria. In each phase the direct energy absorbed from the food and powering individual human bodies has remained about the same. What distinguishes them  is the indirect energy needed for food production, manufacture, and social activity – in other words the energy needed to build social organisation. It is the discrepancy between these direct and indirect social energy use that has defined these three social transitions.

First came natura, the phase of nomadic hunter-gatherers when, for a period of about 55,000 years from c. 70,000 to 12,000 BP small tribes of 20 to 100 people during the Upper Palaeolithic until the world  population reached around 3 million (Morris 2015). These foragers lived within wild nature hunting animals, their plant diet consisting mostly of wild greens, fruits, seed, and root vegetables. During natura the social energy needed for fuel, clothing etc., hardly exceeded the average individual food energy requirement of about 1500 to 2000 kcal/cap/day.

Second came agraria, the phase of settled farming communities associated with domesticated plants and animals from about 12,000 BCE to 1500 CE during the Neolithic Agricultural Revolution whose settlements evolved into Bronze Age cities and civilisations which lasted for around 11,000 years until the population numbered about 450,000 million at the dawn of phase 3. During this second phase the diet was strongly supported by the energy stored in the grains of cultivated cereals and the meat of domesticated animals. The sedentary lifestyle and ready energy source facilitated population growth and the additional social energy needed for food production, rudimentary manufacturing and the building of settlements and eventually cities. Total energy consumption would have been around 6000 to 8000 kcal/cap/day (Morris 2015).

The third phase, industria, occurred around 1550 with the discovery of the concentrated fossil plant energy that could be harnessed from fossil fuels. This provided a windfall of social energy that facilitated unprecedented increase in social organisation manifest as a rapid acceleration in population numbers, manufacturing, technology, along with improved transport and communication that increased trade and global connectivity. We know this phase as the Industrial Revolution which has lasted about 470 years. Food energy was now achieved with energy-hungry industrial agriculture and extensive processing while social energy was eaten up in product manufacturing of many different kinds leading to energy-intensive lifestyles consuming up to 200,000 kcal/cap/day and more (Morris 2015). The result was a human population explosion during which today totals about 7.5 billion. This has been accompanied by a similar burst in the numbers of domesticated animals. The ‘MacCready explosion’ claims that 10,000 years ago humans, their pets and livestock comprised around 0.1% of terrestrial vertebrate biomass, today this total has rocketed to 98% (MacCready 2004). Though a statistic that must have been difficult to derive, even if remotely accurate it is indeed alarming.

Change in human lifestyle have occurred as a result of slow biological change or rapid cultural change. Let’s begin with our basic biology.

The theme of plant energy influencing the historical structure of human society is explored by Stanford historian Professor Ian Morris in his book Foragers, Farmers, and Fossil Fuels: How Human Values Evolve (2015) where he relates long-term human social structure to the means of energy capture and its influence on our values. This interesting thesis can only be briefly and inadequately sketched here.

Baron von Mueller
The Cycle of Life Energy
During photosynthesis plants convert light energy into chemical energy. This energy is stored in carbohydrate molecules which are synthesized from carbon dioxide and water as oxygen is released. Respiration conveys oxygen to tissues and cells as carbon dioxide and water are released
Courtesy CSIRO Publishing. Sustainable Gardens, Cross & Spencer 2009, p. 9

Morris points out that in pursuing their work historians, in effect, zoom in and out of the dimensions of space (local to global) and time (short-term to long-term) and that, as they do so, different material and cultural factors come into focus as the key historical determinants.

Long-term human history, Morris suggests, though influenced by many complex interacting factors, is largely determined by the geographic location of the energy resources needed to build social organization, while short-term history tends to be more about people and places. So, it is energy and geography that have largely determined where and when things have happened in the long term.

The question of why they happened at all is more a biological question about human nature.

And if we want to know how the process works we need to look to sociology. Geography determines the regions where new forms of social organization are likely to originate, develop and flourish – although change in social organization itself can alter the nature of the geographic challenges, as when improved transport systems overcome the tyranny of distance. The mode of energy capture has determined, or limited, population size and density which, in turn, has constrained the development of social complexity and technology. The resultant form of social organization then makes some values more appealing than others.

On this account it is the interplay between geography and energy capture i.e. material factors that are most closely related to different forms of social organization over the long term, rather than, say, culture, religion, science, political institutions, or the actions and ideas of great people.

By ‘social organization’ (or social development) Morris means the quantifiable capacity of particular societies ‘to get things done – to shape their physical, economic, social and intellectual environments to their own ends’ (Morris 2010, p. 24).

Morris relates long-term energy capture to three major phases of human history: foraging (requiring about 10,000 kcals/person/day), farming (from about 10,000-30,000 kcals), and fossil fuels (to 230,000 kcals in recent times).

Phase 1 – Foragers – Palaeolithic hunter-gatherers obtained the energy needed for survival but their form of social organization faced the energy constraints of a life-style which needed mobility to secure a varied diet. Only a year-round secure food supply would allow these small groups to settle, increase in number and develop a different form of social organization. Foragers disdained political and wealth hierarchies but accepted gender hierarchy and violence.

Phase 2 – Farmers – Settled Neolithic farmers harnessed the food energy of domesticated plants using solar agriculture and the muscle-power of domesticated animals, which removed the need for hunting. Eventually the surplus energy made possible by agrarian sedentism was sufficient to support city populations and their differentiated activities. The benefits of scale then facilitated the construction of monumental architecture, sea-going ships, armies, written language, sophisticated commerce and the social structures we associate with modern civilizations. Social stability was maintained by stratification into political, economic and gender hierarchies with legal systems that regulated behaviour and discouraged violence (unless officially sanctioned).

Eventually these communities benefitted from geographic movement as they shifted from fertile river valleys to coastal regions where there was access to distance trade. The energy needed to build cultural infrastructure came from plant energy converted into human and animal labour (sometimes as slavery). A life of toil was the price paid for food and security. The social order was often regarded as the ‘natural order’.

Phase 3 – Fossil fuels – Building on the scientific achievements of the 17th century, consumption of fossil fuels launched the Industrial Revolution in 18th century Western Europe beginning in England. Between 1780 and 1830 Britain’s population doubled from 7 to 14 million and in the century between 1800 and 1900 the proportion of the world’s population living in Europe and North America increased from 16% to 24%. A Western (fossil-fuel) economy dominated global markets with Europeans having control of 84% of the planet’s landmass and 100% of its oceans’.[37] Machines and sophisticated technology reduced the need for muscle power, massively increasing productivity and the demand for effective services and administration later given momentum by the advent of mostly plant-derived electricity, oil and natural gas.

Afro-European commerce was centred on the Mediterranean at the time of the Roman empire, moved to the Atlantic, Indian and Pacific Oceans with Spanish, Portuguese and Dutch exploration before much of this trading empire was embraced by the British Empire. American influence increased in the 20th century, especially in the Pacific. After 1950 we see a gradual Asian ascendancy. Today, most of the world’s people live in cities.

Fossil fuels reduced the need for large families resulting in healthier and better educated citizens with mothers that had time for themselves and salaried work (the ‘demographic transition’). It is this last phase of human history with its rapid increase in trade and communication across the world’s oceans that has resulted in today’s global interconnection and interdependence. We are suspicious of political and gender hierarchies. We resist violence but accept some differentiation in wealth.

Morris’s thesis that correlates human values with the social organization of societies, as determined by the mode of energy capture and use, agrees in broad outline with research reported in the World Values Survey (see cultural evolution).

World values

Inglehart-Wetzel graph of world values
Plot of traditional vs secular-rational values on one axis against survival values vs self-expression on the other. From bottom to top indicates transition from traditional to secular values: from left to right the shift from survival to self–expression values – as a tension between authoritarian (traditional) and emancipative values. With a rise in standard of living and move from an industrial to a post-industrial knowledge society values move diagonally from lower-left corner (poor) to upper-right corner (rich)as values change on both axes. Attitudes of particular countries are also strongly correlated with their philosophical, political and religious ideas
World Values Survey –

The world population which was about 450-500 million in 1500 at the start of the Great Divergence increased to 1 billion around 1800 then expanded rapidly with fossil-fuel powered globalization to 2.5 million before gathering global momentum in the ‘great acceleration’ to increase from 2.5 to over 7 billion by 2018.

‘Across the two centuries since the Industrial Revolution began and capitalism took off, the world’s population has grown 7-fold, its biggest city 25-fold, its stock of knowledge (by Morris’s calculation) 860-fold, and its energy capture more than 40-fold’.[1] Prior to 1800 world-wide life expectancy at birth averaged less than 25 years – in 2018 it is 70 years.


From nature to culture via plant energy

For almost all human history we have lived as nomadic hunter-gatherers until, beginning about 12,000 years ago, there was the progressive adoption of settled agriculture. The food energy needed for survival and once obtained from wild plants and animal hunting was then obtained from cultivated cereals and domesticated animals. With efficient cereal cultivation fewer people were needed to provide food, so in urban settlements people were available to follow other cultural pursuits through a diversification of labour and more complex social organization, facilitating not only population growth but also economic and other development or ‘growth’ as a form of wealth. Back in 1300, across the world, and bar social elites, most people still shared a similar lifestyle, living by labour-intensive subsistence farming. Wealth generation (as freedom to move off the land) was greatly accelerated when the concentrated energy of fossil fuels was combined with the use of machinery during the industrial and agricultural revolutions around the 18th to 19th centuries, first in western Europe but spreading to the rest of the world. Today more than half the world population lives in cities and only about 25% work in the agricultural sector, although this is less than 1% in the United Kingdom and United States (World Bank 2017).

Thus humans first lived within wild nature, the factors influencing lives coming from nature itself. The adoption of cultivated crops and domesticated animals as a food source gradually transformed human existence especially in the cities where the physical surroundings were now a consequence of man-made culture. The transition from nature to culture created new socially functional urban spaces and new ways of thinking that contrasted (among other things) nature and culture, wild and cultivated, urban and rural, even poverty and wealth with the new complications of ownership of land and property.

Wealth, social structure & values
Though we have always been totally dependent on plant food as a critical life resource, its economic value as a commodity has depended on the forces of supply and demand and the labour needed for its cultivation, storage, and distribution. For much of human history food was a fundamental currency of life but major social changes occurred as new energy sources reduced the input of human labour needed for its production, first by the use of animal muscle and more effective tools, like ploughs, then more complex machinery powered by fossil fuels leading to industrial agriculture. In recent times there has been the addition of assorted chemical growth facilitators, plant breeding and biotechnology including genetic engineering. With fewer people employed in food production there has been a rural to urban transition as people have moved into the cities where increasingly sophisticated technologies with access to global resources has resulted in ever more complex and diversified lifestyles.

This increase in diversity, the global reach of trading networks and political networks has produced a complexity of technology and social organization that is hard to grasp. Perhaps we get an inkling of this when we realize that our computers and mobile phones are the products of long-accumulated and increasingly sophisticated scientific and technical knowledge and the sourcing of scarce resources from around the globe. The increase in social complexity implied when comparing a knapped flint arrow head with a computer mouse is mind-blowing. Whether this transition has been a ‘good thing’ is another matter.

The meaning and significance of plants in peoples’ lives
What has been the role, the significance or meaning of plants in peoples daily lives through the course of history. If this has varied then how and why has it changed?

Changes in food production – moving off the land
We have seen how, over time, increasing efficiencies in food production there has been a gradual movement of people off the land, out of wild nature with wild plants, onto cultivated land and into cities in a transition from wild nature, to rural agriculture, to urban culture. Today’s city-dweller encounters food plants briefly in grocers and supermarkets, but in considerable diversity, having little idea of how they are cultivated or, indeed, where they have been grown. Seasonal constraints have often been addressed, so if we discover that the food was sourced from another country, perhaps on the other side of the world, we are unlikely to be surprised.

In sum, the supply of food has, over time, become more secure: we have access to a greater variety of food in unlimited quantity but with little awareness of its source or method of cultivation.

Plants as luxury goods
For almost all human history scarce, beautiful, or useful plants have been prized by society. As availability has increased so their economic value has declined. From early times affluence has distanced people from the land. Wealthy ruling elites, who did not need to worry about the source of the next meal, could display their wealth by, for example, enhancing their food with rare herbs and spices and get access to the best plant-based medicines. This was the pattern during classical times up to the time of the colonial spice race to the East Indies until spices lost their fascination. But the social prestige of plant rarity would not go away but be replaced by a host of different luxuries of economic botany sourced from round the world – exotic beverages like tea, coffee, cocoa, and in more recent times coca, not to mention spirits and wines. New plant commodities like sugar, tobacco, and cotton would generate fortunes and social customs that have persisted, with consequences that have been for both better and worse. During the time of European colonial expansion plants were prized as ornamental garden novelties to be displayed in prestigious rare collections, starting with the financial bubble of tulipomania. These would gradually pass into commercial nurseries to become more generally available.

Once again, efficiencies in production have made socially influential economic and ornamental plant rarities more widely available. Wealth appears to no longer find plants such an attraction. In recent times the diversity of ornamental plants has reached saturation point though novelty always appeals.

Historically the control of food production and agricultural labour has been the catalyst for social transformation by generating the wealth needed to add complexity to social organization – including political, economic, cultural and religious structures, science, exploration and trade. The first circumnavigation of the world and production of maps that outlined the world’s great land masses circumscribed limits for biological inventory and a global economy as sophisticated social organization meant that societies could take full advantage of the benefits of distance and scale.

This background has briefly discussed the effects on human society of the harnessing plant food-energy, first from the wild, then the energy produced by the solar agriculture of cultivated plant crops, followed by the addition of the concentrated sun’s energy in dead plants as fossil-fuel-based industrial agriculture, modern synthetic chemicals and biotechnology. This provides a framework for energy considerations of the future. It also draws attention to the elaboration of interest in plants that followed the elaboration of European society during the Great Divergence, which will be discussed in the next article.

Key points

Whatever our opinion of Morris’s thesis about changing human values his work draws attention to important long-term features of the human relationship to plants:

• Total dependence of humans on the capture of life-sustaining plant food-energy and the way that ‘growth’ (in population; economy; diversity, complexity, polity – i.e. social organization) is closely energy-related

• The close relation between mode of energy capture and social organization over the long term transition from hunter-gatherer societies to agrarian societies where people are mostly occupied with food production, storage and distribution

• How the location of first agrarian human settlements was related to geographic regions suitable for plant energy capture, that is, conducive to plant and animal domestication

• How readily available energy in sedentary communities facilitates rapid population growth

• How large populations can harness the benefits of scale (division of labour, ocean-going ships, armies, communal technology)

• How in settled communities when food can be provided by fewer people this is a form of wealth, releasing more people to engage in other cultural pursuits that benefit the community as a whole – that is, increasingly complex social organization

• How all the above factors have accelerated as ‘growth’ was increased using the ancient energy of the Sun stored in fossil fuels

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