In the first article of this series, Constructing Our Niches: How Evolutionary Theory Is Useful for the Building Industry, I introduced the idea that operating deliberately within an evolutionary theoretical framework offers benefits to the building/construction industry and justified why I was the person suited for making this argument. Now it’s time to wade into the evolutionary pool, starting with a more thorough discussion of why evolutionary theory is applicable to contemporary humans and our social/cultural worlds.

As I discussed last time, this applicability rests on the following five assumptions that are spelled out by Leonard (2001:71):

  1. Humans are life forms.
  2. Natural selection operates on phenotypes, making evolution in part a phenotypic phenomenon.
  3. Behavior is part of the human phenotype, and it is transmitted partially through learning.
  4. Technology [along with other aspects of our social/cultural worlds] is the product of human behavior, and consequently a component of the human phenotype.
  5. The differential persistence of behavior will be reflected by the differential replication of technology [or other aspects of culture] through time [and/or across space].

Again, the phenotype refers to all of the characteristics of an organism (or group of organisms) that “… include biological features, such as skin color, height, muscle strength, basic behaviors, etc., as well as cultural features such as tools, artifacts, dwellings, institutions, etc. that are the results of behaviors (Dawkins 1982, 1989; Dunnell 1989, 1995; Leonard 2001; Leonard and Jones 1987; O’Brien and Lyman 2000a)” (Harmon 2005:204). The phenotype for individuals results from the interaction of that individual’s genes with the surrounding physical and social environment. For cohesive groups, it results from the interaction of the group’s individual members with the surrounding physical and social environment. The transmission of this phenotypic variation occurs biologically (genetic inheritance via sexual or asexual reproduction) as well as culturally (information inheritance via teaching/learning, imitation, reverse engineering, etc.).

This means that human behaviors, the physical objects we create and use (such as the built environment), and their associated intellectual traditions (including those of the design/construction industry), are part of our collective toolkit for adapting to the larger social/cultural and physical environments we live within, individually and as members of nested groups of ever-increasing size. Given this, we can use Darwinian evolutionary theory to not only understand human biological change, but also human cultural change and transmission.

To illustrate this, let’s examine the use of forced air as the dominant modern method in the U.S. to heat and cool buildings. In such systems, air is used as the primary medium to transfer heat energy, either into a space through the introduction of warmer air, or away from a space through the introduction of cooler air (though the manipulation of humidity levels also plays a role in this). Yet air is a relatively poor medium to use for capturing and moving heat – it’s a far better insulator. Water, also used to capture and transfer heat around in modern HVAC systems, is 832 times denser than air, and can therefore do this quite a bit more efficiently per unit volume than air can. Air’s specific heat value (the amount of energy required to raise a unit volume of material by one degree, an indicator of a material’s ability to capture and move energy) is just under 25% of the value for water (Moe 2010:72).

Nor are air-based systems as effective at maintaining thermal comfort compared to systems that use some combination of radiant heating/cooling, low-velocity underfloor air distribution and natural ventilation. In part, this is because in most situations only 27.5% of the human body’s exchange of heat energy with its surrounding environment results from convective transfer, that is the transfer of energy via the movement of molecules within a fluid or gas (i.e., air coming into contact with building occupants). Whereas radiant transfer, via the absorption of electromagnetic waves from a source at a greater energy intensity level (such as a radiator, thermally active building surface, or another warmer human body), accounts for the bulk of this exchange at 47.5%. The other 27% results from exhalation and a few other physiological processes.

It is true that conduction, heat transfer via the direct contact of objects, can dominate all other modes of heat transfer – think back to wrapping your hands around a hot cup of coffee or walking on the cold tile of a bathroom floor with bare feet first thing in the morning. However, conduction is a much less common occurrence and certainly not a primary method used to maintain thermal comfort in the built environment (Moe 2010:68-70).

Thermal comfort is dependent on other factors as well, such as variation in the insulative properties of clothing, occupant activity levels, metabolism rates, the degree of personal temperature and ventilation control, expectations, and connections to nature, to name a few. But these factors don’t change the basic limitations of air based heating/cooling systems. Which begs the question, how did these comparatively inefficient and ineffective systems out replicate other forms of heating and cooling in the U.S.? Why did the “behavior” that produced this technology have greater persistence than the “behavior” producing other technologies, such as radiant based heating or cooling? What was it about air-based systems that provided a greater selective advantage from an evolutionary perspective over other means of heating and cooling? Perhaps more importantly, who was that advantage provided to?

Looking at just the ability to control the rate of heat gain or loss from one’s own body, or that of your children, grandchildren, etc., then behavioral/technological adaptations that allow you to control this rate of change through such things as clothing, fire pits, fireplaces, fans and centralized heating/cooling systems do offer a selective advantage to individuals and their genes. The more extreme the environmental temperature, the greater the advantage of being able to control one’s rate of heat gain or loss. Such control allows us to minimize our exposure to temperature extremes that result in death or the physiological stress resulting from prolonged or chronic thermal discomfort, which can shorten life expectancy or even lead to emotional distress (Brager et al. 2015; Cheung et al. 2016; Hanna and Tait 2015; Lucas et al. 2014; Mishra et al. 2016; Xiang et al. 2014).

One’s ability to survive long enough to reproduce and the rate of survival of one’s offspring are then positively impacted by this general behavioral/technological adaptation. While certainly critical for our long distant hunter-gatherer ancestors, this part of our phenotypic toolkit still increases our relative “fitness” to this day. It positively impacts our species’ rate of reproduction relative to not having this adaptation. And over time, more fit technologies out replicate, or replace, less fit technologies that are less effective in increasing our reproductive fitness (O’Brien and Lyman 2000), such as the eventual supplanting of fireplaces by central heating systems as the dominant means of heating during the 19th and 20th centuries.

However, fitness isn’t only defined with respect to the reproductive success of individuals or our genes. Recall from the first article in the series that evolutionary forces can operate at multiple levels simultaneously – genes, cells, organisms/individuals, and groups of organisms/individuals (Sober and Wilson 1998; Wilson 1998, 2015, 2017 – see the last for a summary of the basic tenets of MLS Theory). The ability to control the rate of heat gain or loss would also have increased the relative fitness of the nuclear family units or larger kinship groups of our hunter/gatherer ancestors. It also increases the fitness of contemporary businesses relative to other competing organizations. All else being equal, the more employees can effectively control their rate of heat gain/loss according to personal preferences, the more thermally comfortable and subsequently more productive they are (Horr et al. 2016; Kats et al. 2003; Seppanen et al. 2006). Let’s now explore how these relative fitness benefits at varying levels of selection likely influenced the development of HVAC systems in North America.

Over the course of the eighteenth and nineteenth centuries, the needs of increasingly large and complex industrial, hospital and prison facilities was a primary driver for the development of heating and ventilation technology. These facilities needed to address the presence of “foul” air as well as heat larger volumes of space containing larger numbers of people. As a result, the primarily radiant based fireplace of the eighteenth century evolved into the centralized, mechanically powered convective based heating and ventilation systems of the late nineteenth century (Moe 2010:34-53).

At the time, coupling convective heating with ventilation was the most effective way to meet both needs. Fire was originally used to generate the convective currents of air in these early ventilation systems, and so it was easy to couple the functions of convective heating and ventilation together into one system. It also made sense to continue this coupling as heating and ventilation systems further developed. By the end of the nineteenth century, artificial heating and ventilation were fully integrated and centralized within the same distribution system.

The 19th century also saw some early attempts at artificial cooling, such as more elaborate uses of ice to cool moving air as well as the introduction of early compressors (Cashman 2017). But it was the “thermal comfort” of industrial machinery that really drove the development of artificial cooling during the late nineteenth and early twentieth centuries. As industrial equipment increased in size and number, there was a growing need to both dissipate the heat generated by this equipment, as well as more tightly control the humidity levels within industrial/manufacturing spaces, such as printing and textile facilities. Enter Wills Haviland Carrier, the “Father of Air Conditioning” (Ingels 1952).

Building on previous research and engineering applications of air conditioning in manufacturing facilities, Carrier developed his psychrometric chart and formulae which quantified the relationship between temperature, humidity and dew point. Contemporaries of Carrier independently formulated similar diagrams and formulas, but partially because of his ambition and marketing abilities, Carrier’s chart, formula, and underlying principals ultimately formed the basis of contemporary air conditioning engineering.

Those manufacturing companies incorporating air conditioning for their industrial equipment increased their production rates and efficiencies. It put them at an advantage – it increased their relative fitness – compared to other manufacturers who didn’t adopt air conditioning or were slower to do so. And the fact that air conditioning could make use of the same centralized heating/ventilation distribution systems already being used in manufacturing facilities made it that much easier. Evolutionary forces operating at a group level, namely manufacturing companies, essentially selected for air conditioning as a phenotypic adaptation of manufacturers. This isn’t to say that the selective advantages to shareholders or individual employees wasn’t a factor as well, but the competitive economic environment that existed likely resulted in the level of selection stronger at the group than that of the individual.

Cooling equipment gave way to cooling people as awareness grew. With the ability to artificially cool environments now actually available, the comfort provided in hot and humid conditions (along with the decreased health risks during temperature extremes) coupled with the aggressive marketing from Carrier and other early HVAC system manufacturers, artificial cooling was initially seen as a symbol of status before eventually becoming the norm (Basile 2014).

The demand for commercial and multi-family/single-family residential applications of forced air HVAC systems (including window AC units) steadily grew over the early to mid-20th century. These early HVAC systems along with electric lighting also allowed developers, builders, and business owners to “free” themselves from the constraints imposed by the need to passively heat/cool, ventilate and daylight spaces. Building orientations and configurations no longer had to maximize cross-ventilation, passive solar heating or daylight penetration (Addington 1995:460; Ali and Armstrong 2010:1-4; Wood and Salib 2013:16-17).

This reduction in contextual environmental constraints, along with the desire of builders and developers to minimize construction costs and shorten construction schedules, contributed to an increase in the standardization of building materials (Beamish and Biggart 2010:260). This further contributed to the increase in home ownership by the mid-20th century (Johnson and Kennedy 2006). Businesses could also increase the square footage of their buildings relative to the size of their lots since employees no longer had to be located near windows (Ali and Armstrong 2010:2), allowing for an increase in the ratio of employees per square foot (e.g. Lu 2015: 17-18; Rassia 2017:10-12).

All of this resulted in varying levels of economic benefits for homeowners, developers, designers, builders, building/construction industry manufacturers (i.e., Carrier), business owners, employees and even municipal, state and the federal government through the increase in tax revenues, increasing their relative fitness. I would propose that the dominance of modern forced air HVAC systems in the U.S. are essentially the result of:

  • The relative economic and health/comfort benefits across multiple levels of selection that artificial heating/cooling offers (compared to no artificial heating/cooling),
  • The constraints to subsequent technological developments imposed by a) the coupling of convective heating and ventilation during the 18th and 19th centuries and b) the need to more tightly control environmental temperature and humidity for manufacturing equipment during the late 19th and early 20th centuries, and
  • The financial benefits and increased relative fitness provided to Carrier and other forced air HVAC manufacturers through the aggressive promotion of forced air HVAC systems.

The constraints mentioned above in the second bullet point are part of the social/cultural and physical environment that evolutionary forces, such as natural selection, operate within. The conditions of the environment at any given time limit the direction that evolution will proceed forward. While some combination of radiant heating/cooling and natural/forced air ventilation would best address the human physiological and psychological processes relevant to human comfort, the technology and engineering knowledge readily available at the time, combined with the other two factors listed above, made the path to dominance significantly easier for forced air systems.

The uniformity provided by a single dominant type of HVAC system played a role in this as well. In general, uniformity imposed on group members (such as that through social/cultural norms) enhances the cohesiveness, cooperation and functional integration of groups (Boehm 1996, 1997a, 1997b; Sober and Wilson 1998; Wilson 1998). Norms (including formal laws, regulations, standards, etc.) help create common experiences and expectations among group members, binding them together. As a result, they help suppress within-group selection among group members that can disrupt the cohesiveness of groups, ensuring that between group forces dominate (Wilson 2015). During the late 19th and early 20th centuries, the standardization of materials, systems, and building configurations increased the uniformity within manufacturers, designers, builders and business owners. Even if a given design solution wasn’t the most optimal (such as forced air compared to radiant relative to thermal comfort), the uniformity offered by standardizing on a solution in and of itself provided a selective advantage to these organizations, the building/construction industry, and society at large.

In fact, at the level of the nation-state, particularly one like the U.S. with diverse social/cultural subgroups, such technological standardizations that cut across these varying subgroups help unify the larger nation-state. And one could argue that developers and building owners who lagged incorporating HVAC systems into their facilities would have been outcompeted by their competitors, potentially going out of business. The new building/construction environment at the time, partially defined by HVAC use, would have selected against those developers and builders.

For the purposes of this article, I’ve simplified this exercise of framing the U.S.’s history of HVAC within an evolutionary theoretical framework. There are obviously more details and nuances within the history itself, as well as with the evolutionary applications. Such specifics could be fleshed out in more detailed overviews and studies. One of many potential examples would be the use of phylogenetic analysis (or cladistics), along with other statistical methods, to systematically examine the development and distribution of HVAC system characteristics from the nineteenth through twentieth centuries, across the U.S., and across various sectors (residential, commercial, healthcare, etc.) (e.g. Harmon 2000, 2005, 2008; Harmon et al. 2006; Mace et al. 2005). This would provide a more detailed picture of the developing uniformity of HVAC systems around air-based technology over this time, and across the U.S. and various sectors, clarifying the overview presented above.

And the story obviously doesn’t end here. While forced air systems still dominate in the U.S., that dominance is waning, driven in part through such things as the energy crisis of the 1970’s, recognition of the threat of anthropogenic (human-caused) climate change, the phenomenon of sick building syndrome, and the proliferation of sustainable and wellness certification systems. The selective environment has changed.

“Hybrid” systems that integrate water as a means of transferring heat (and even beam heat into space), passive heating/cooling methods, and systems that use some combination of radiant heating/cooling, low-velocity underfloor air distribution and natural ventilation are becoming more the norm. There is greater recognition among decision makers that energy consumption, greenhouse gas (GHG) emissions, the impacts of thermal discomfort, and other aspects of sustainability and health/productivity have an impact on their bottom line. And with regards to climate change, we’re recognizing the need for more sustainable and regenerative built environments that better meet the productivity and health needs of building occupants and organizations, as well as minimize, and even reverse, the built environment's contributions to GHG emissions.

The relative selective advantage offered by increased thermal comfort, decreased energy consumption, and decreased GHG emissions is now enough to overcome the advantage offered by the previous industry standardization on forced air systems. The baseline is no longer a lack of mechanical heating/cooling or just cooling. Competition among building systems, the firms who design, install and manufacturer them, as well as the organizations who use them, is now relative to the quality of heating/cooling provided and energy consumed, not the use of heating/cooling vs. no or limited heating/cooling. Changes in the physical and social/cultural environments are selecting for changes in the types of heating/cooling systems we manufacture and install in our built environments. Though the Trump administration, segments of the fossil fuel industry, as well as other organizations like the Heartland Institute, continue in their efforts to limit or reverse some of these changes in the social/cultural environment.

Nor does natural selection care if we’re deliberately taking actions with evolutionary consequences in mind. The ability to understand the consequences of our actions, policies, etc., from an evolutionary perspective offers significant potential to help guide better decision making moving forward. It gives us an added selective advantage, but only if we recognize this and choose to act on it. During the early 20th century, if we had better understood anthropogenic climate change, the determinants of human thermal comfort, and the impacts of discomfort on productivity and health, then the history of HVAC in the U.S. might have been different. In the next article, I’ll begin exploring how to do this with a discussion of Elinor Ostrom’s Nobel Prize-winning research on avoiding the tragedy of the commons phenomenon.


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