Human Evolution And Entropy
- Human population growth has dominated the planet. In a Darwinian context, this phenomenon is attributed to “survival of the fittest” where intelligence has been the key differentiator between humans and other species. This framework can be broadly rephrased to state that the universe is orientated towards species that maintain the fastest growth.
- Human population growth could not have occurred on the same scale without increasing energy consumption (made possible by human intelligence). Greater energy consumption increases entropy.
- As a thought experiment, one could reverse the order of these two observations and broadly state that the universe is orientated towards species that increase entropy the most. The subtle difference of this perspective relative to the “survival” view is the implication that the universe will promote outcomes in which the greatest total amount of energy is consumed over the long run. This view is consistent with human's’ unique ability to increase the Earth's radiant heat loss via global warming. More conventionally, it is also compatible with human’s desire to increase GDP per capita.
- This thought experiment suggests that humans -- as agents of increasing entropy -- have a “special place” among species only as long as they are able to consume the most energy. It also suggests the ultimate limit on human population growth is their ability to access energy.
Thinking about entropy can be a pleasant but time consuming diversion. I started thinking about entropy and humans “thanks”(?!) to Cesar Hidalgo’s engaging book Why Information Grows which articulates the concept that complex order grows in out-of-equilibrium systems. However, energy is required to keep out-of-equilibrium systems from returning to equilibrium. Your refrigerator is an excellent example, as it uses energy to keep a cool interior from rebalancing to the temperature of your kitchen.
There are three common ways in which the concept of entropy is expressed. For my purposes, the simplest thermodynamic form expressed by the French military engineer Sadi Carnot in the 19th century is sufficient: ΔS = ΔQ/T. It states that the increase in entropy, S, is equal to change in heat Q relative to absolute temperature T. The second law of thermodynamics states that total system entropy cannot decrease: it can either remain the same or increase. Going back to the refrigerator example, while entropy in the interior of refrigerator is decreased due to cooling, the waste heat from the motor cooling your refrigerator causes a net increase in overall entropy.
Figure 1: Schematic Illustration of Universe’s Entropy Increase
While cosmology is a hotly debated topic, there is broad agreement that entropy was very low 13.8 billion years ago when the Big Bang occurred, and that it has increased ever since. While there is controversy as to whether “heat death” (in which all energy is fully distributed across the universe) is the final state of the universe, heat is being distributed in the universe now. A specific example of this is provided by our sun. It will dissipate heat from nuclear fusion for several billion more years before transforming into a “red giant” engulfing Mercury, Venus and probably the Earth. The point of this review is simply to make the point that the universe is evolving to increase entropy and it does so by consuming and dissipating all available free energy.
Unique Earth, Unique Species (In Our Solar System, Perhaps Not In The Universe)
Other planets in our solar system absorb solar radiation, but Earth is the only that has stored significant amounts of solar energy in the form of organic material. Similarly, humans are not the only species that consume solar radiation and stored solar energy. But humans have proven to be a unique species because of their ability to dramatically increase the rate of their energy consumption. First through the use of fire, then by domesticating other species, and more recently via fossil/nuclear fuels and “renewables.”
Table 1: Human Energy Consumption By Method
As Figure 3 illustrates, humans continue to increase their consumption of energy at a faster rate than the growth in the overall population. While human progress is often credited to a competition of ideas, it is interesting to note that the net effect of all of those ideas is to consume more energy!
Figure 3: World Population Growth and Energy Consumption 
However, GDP has increased even faster than energy consumption, meaning humans have gotten better at converting energy into material well being.
Human’s explosive population growth could not have been accomplished without commensurate dramatic increases in energy consumption. Seven and a half billion people would have a hard time feeding themselves if they were still hunter/gatherers warming themselves by a fire. But this also means humans have been phenomenally successful in increasing entropy. So much so that their efforts are visible in some amount of global warming.
The only way the Earth can transmit heat is by radiative cooling (as space’s atmosphere does not permit convective or conductive heat dissipation). There is vigorous debate regarding how efficiently the Earth transmits heat. The less efficient it is, the longer global warming caused by Man’s activities will last. But regardless of how much warming occurs on Earth, increased heat due to human’s energy consumption causes faster increases in entropy as that heat is eventually released into space.
How Much Longer?
This thought experiment has implicitly suggested that human’s good fortunes were created because they were the agents most capable of facilitating the universe’s tendency towards increased entropy. If increasing entropy is the objective, presumably human’s survival will be enabled at least until all fossil and nuclear fuels have been used up. After that point, humans have substantially less relative “entropy advantage” over other species. That is, unless they can remain more energy intensive by exploiting solar and other “renewables.”
While there will inevitably be a time when Earth’s traditional sources of energy will be exhausted, that time is likely well into the future based on remaining energy potentials illustrated conceptually in Figure 5. In postponing that time, human’s declining fertility, their ability to increase the ratio of GDP to energy consumption, and past successes in developing new technologies are all encouraging.
Figure 5: Schematic Of Remaining Energy Potential
While this theoretical framework may seem far fetched, other thinkers have travelled down a similar road. Alfred Lotka proposed complementary dynamics in the early 1920s (bolding is mine):
“He was especially keen to explore the energetics of evolution: that is, how to understand evolution broadly as a process involving the capture and transmission of energy. Lotka envisioned systems as giant machines or energy transformers that changed over time. For him, natural selection could be understood as a physical principle with the same level of generality as the laws of thermodynamics (13). Lotka argued that natural selection would tend to favor an increase in the rate of circulation of matter through the system, and would also favor more efficient use of energy. Seeking to derive a general law expressing this idea, Lotka proposed the principle that ‘evolution proceeds in such direction as to make the total energy flux through the system a maximum compatible with the constraints’”
It is not clear to me that this perspective provides any useful predictions that are different from those made from viewing the universe in a more conventional Darwinian framework. But now and again, it can simply be refreshing to view existence in a novel way.
 Other species like the Passenger Pigeon grew tremendously, but were unable to maintain their growth and later collapsed.
 Excludes energy from food, fire and agriculture except to the extent primary fuels, solar, wind, or hydroelectric were used as inputs.
 Increasing greenhouse gases, high cloud cover, and water vapor all slow the rate of the Earth’s cooling. The Earth continues to warm until the point when heat lost from additional radiative cooling equals the additional heat generated on Earth.
Transparent and reproducible: I only generated Figure 3 from World Bank data using the free, publicly-available R program, the data links in this article, and the R code available in “energyEntropy.r" on github.