MacCready Explosion

The MacCready Explosion is a term coined by philosopher Daniel Dennett. based on a 1999 publication of aeronautics engineer Paul MacCready, under the conceptual title “Nature vs. Humans” Contemporaneously with and earlier to the published paper, MacCready conducted a number of live presentations on the subject, some hosted by TED.com. A number of such presentations were conducted in conjunction with MacCready’s professional interest and research in efficient transport systems and aeronautical innovation.

“Nature vs. Humans” attempts to encapsulate the dramatic effects of Homo sapiens rise to dominance on earth over the last ten millennia and the last century.

The eponymously named phenomenon has been variously articulated by population theorists, environmental scientists and historians such as Garrett Hardin, Vaclav Smil, Jared Diamond and Juval Hariri amongst others. Much of this literature can trace its origins back to the work the 19th century population theorist Thomas Malthus and others of that era, under what is now broadly termed neo-Malthusian theory, substantially qualified by earth science theories and research of the 20th and 21st century.

While MacCready (1925–2007) rose to prominence in the field of aeronautics, developing record breaking human powered and solar powered heavier-than-air vehicles, his other less well-known activities pertain to his activist research and pronouncements (often skeptical) on human development and the environment, of which “Nature vs. Humans” was a prominent one.

Nature vs. Humans

In his exposition of the phenomenon, MacCready uses as the long time frame the last ten millennia of human history and the dramatic increase of human, livestock and pet populations at the expense of, and reduction of, naturally occurring (wild, non-domesticated) terrestrial and avian vertebrae, all expressed as biomass. This time frame spans from the broadly accepted commencement of the First Agricultural (or Neolithic) Revolution, circa 8,000 BCE, to the end of the 20th century.

His papers on the subject, now under the curatorship of California Institute of Technology, and as used in the TED.com presentations, show in series graphical form a shorter time frame (1850 – 2050) to emphasize especially the dramatic unchecked increase in human, livestock and pet biomass, commencing in the early 20th century, along with ongoing decreases in wild terrestrial and avian vertebrate biomass. In his presentations he infers that ultimately human population growth trends must be logistical rather than exponential given the finite carrying capacity of the planet. The graphics makes no reference to the source of his population data used to promote his views, other than directing readers to contact the author for underlying data used and assumptions made. His assumptions appear to broadly concur with researched/published data of Vaclav Smil, a widely respected and published inter-disciplinary researcher.

In essence, MacCready’s claim was that at the start of agrarian based civilization some 10,000 years ago, terrestrial and avian vertebrate biomass (excluding humans, their livestock and pets) represented ~99.9% of such living creatures while humans, their livestock and pets represented only ~0.1 %. At the date of publishing and presenting his phenomenon in 1999 (and allegedly revised in 2004), he claims the figures had dramatically reversed to ~2% and ~98% respectively. Per MacCready’s shorter time frame analysis, at circa 1900, the figures provided indicate biomass ratios of ~56% and ~44% respectively. It should be kept in mind that Macready’s long time frame analysis of 10 millennia straddles the Quaternary Megafauna Extinction between ~50,000 and ~3,000 years ago and in which it is estimated that approximately half of all mammal species over 40 kg was eliminated, much of this through human activity.

Given comparative time frames of terrestrial vertebrate life first appearing on earth (~350 million years ago), mammals at least 178 million years ago, and modern humans (at least 200,000 years ago), the exponential growth of humankind (along with human induced growth of livestock and pets) in only the last century is remarkable.

His conclusions, poetically and dramatically stated and widely quoted, are:

"Over billions of years on a unique sphere, chance has painted a thin covering of life – complex, improbable, wonderful and fragile. Suddenly, we humans, (a recently arrived species, no longer subject to the checks and balances inherent in nature), have grown in population, technology and intelligence to a position of terrible power: we now wield the paintbrush."

Factors leading to the phenomenon

Broad consensus amongst anthropologists and evolutionary biologists indicates that factors underlying the phenomenon are due principally to human cultural revolutions. Such revolutions are claimed to have occurred in, amongst other things, language development, societal cooperation, tool making and agriculture. Such arising culture in turn arose from the prior evolutionary and co-evolutionary development in Homo sapiens of the large brain and resulting intelligence, along with possibly other anatomical features such as a deepened vocal tract that permitted sophisticated vocalization and communication

The conflating by MacCready of human biomass growth, along with livestock and pets, would appear to be the key to appreciating the phenomenon. Domesticated animals such as cattle and pigs especially, have contributed greatly to biomass growth, and consequential increases in greenhouse gases, land and water usage, deforestation, and environmental damage. Indeed, livestock (and cattle in particular) are fractionally the biggest contributor to human induced biomass growth by a wide margin.

Inferred in the above phenomenon is the increasingly larger land tracts required not only for pasturage but to cultivate domesticated crops to provide plant-based sustenance to the specified cohorts and which compete directly with wild plants of all type (the largest in biomass by far of all living organisms). Not inferred or included in the above analyses are microscopic organisms and insects which, even though their collective biomasses (and bacteria specifically) dominate non-plant kingdoms on the planet. They are explicitly excluded by MacCready, on the basis that they presumably do not compete at the macro scale for planetary space or resources with the specified cohorts.

Increasingly more sophisticated and exhaustive research data has become available in the 21st century on biomass distribution on the planet and is constantly being revised and improved. A 2018 meta-analysis indicates that to a first approximation, humans and livestock represent less than 0.03% of all biomass (expressed as giga tonnes of carbon content, a derivative of dry biomass) in the earth’s biosphere. This then indicates, from a different perspective, the critical extent to which the very small human induced biomass could affect much of the remaining biosphere. The effect on marine, estuarine and fresh-water life (where fish alone represent ~80.5% of all planetary vertebrate life) is of particular concern in the modern world, and is not addressed in the phenomenon.

MacCready’s overriding message derived from the phenomenon is that all growth must ultimately face the limits imposed by a finite natural world and that mankind needs to continually strive for better efficiency in all spheres to retain any reasonable quality of life for all. His analysis and describing of the phenomenon are not exhaustive or even scientifically rigorous, but appears to provide a framework for the future, being used by other earth scientists, especially as regards conflating human induced biomass growth and then comparing that to other categories. It should perhaps rather be seen as a late 20th century clarion call to humanity, effectively visualized in simple graphical form, to reflect on and modify its activities on earth given the profound direct and indirect effects it has on the biosphere.

References

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