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For more than two centuries, the rapid increase of the human population has shaped public perception about planetary limits. In 1798, the Reverend Thomas Malthus published his influential An Essay on the Principle of Population, in which he contrasted the exponential curve of population growth against the linear increase in food production. “The power of population is so superior to the power of the earth to produce subsistence for man, that premature death must in some shape or other visit the human race,” he wrote. Since Malthus’s publication, the threat of a so-called Malthusian catastrophe has influenced modern discourse about the future of civilization.

Given this ominous prediction, it is a relief to consider the alternative paradigm presented in A New Reality: Human Evolution for a Sustainable Future (City Point Press, 2018). First published in 1981 and recently revised, the book was co-authored by the late scientist Jonas Salk and his son Jonathan Salk, a psychiatrist. The senior Salk is widely recognized as the developer of the polio vaccine as well as Louis Kahn’s visionary client in the commission for the Salk Institute for Biological Studies in La Jolla, Calif. Although he is widely respected for his contributions to medicine, Jonas Salk is lesser known for his scholarship on population growth—a priority during his final decades of life.

In their book, the Salks introduce a revised trajectory for population growth called a sigmoid curve. Unlike Malthus’s relentless upward slope (with inevitable collapse), the sigmoid is an S-shaped function that initially parallels the Malthus model—but then decelerates after a point of inflection. This second phase represents the gradual stabilization of growth, without catastrophe, as well as the sustainable utilization of available resources.

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This Salks’ model is based not on naive optimism but on science: as biologists know, a given population of organisms will adhere to a sigmoid growth trajectory within a closed system. From fruit flies to yeast cells, an initial period of accelerated growth (Epoch A) eventually transitions to a stable plateau (Epoch B) based on environmental carrying capacity. Although this general shape is predictable, the slopes can vary considerably. The more food provided and the greater the frequency of waste removal, the more vertical the Epoch A slope becomes. If the supply of resources or removal of waste suddenly declines or stops, the population stabilization will then resemble a Malthusian catastrophe. Thus, while the Salks’ paradigm presents a more holistic and scientifically derived model for the growth of a given population in its environment, it does not guarantee a “soft landing” Epoch B.

In a September lecture to the Design Futures Council Leadership Summit on the Future of Environmental Responsibility, held at the University of Minnesota, Jonathan Salk emphasized humanity’s role in determining the nature of this second growth phase. He explained the profound ways in which Epoch B shifts common assumptions. For example, Epoch A is defined by a dilemma between pragmatic (e.g., consumption) or humane (e.g., conservation) choices. However, in Epoch B, the most humane outcome is also the most pragmatic (e.g., avoiding catastrophe). Salk argued that architecture and design are essential Epoch B disciplines, based on their capacity to shape a future environment defined by humane pragmatism. In my follow-up interview with him after the lecture, Salk addressed several questions raised by the book and his lecture.

For example, the sigmoid curve inflection point—the threshold between epochs—has uncannily similar timing as the beginning of global overshoot in Malthus's model. Both of these events supposedly occurred during the latter decades of the 20th century. While not inextricably connected, they are “two interacting phenomena occurring at the same time,” Salk says. Population growth slows as human needs are met, infant and child mortality decreases, and individuals don't need to have as many children. Thus, the slowing of growth is not caused by the approach of limits, per se, but the two are happening at the same time. For Salk, the outpacing of the Earth's resources is a mathematical consequence of the simultaneous increase in human numbers and the growth of energy-consuming technology. Although exceeding these limits is influenced by population size, other determining factors, such as technological development, exist. “I must add, however, that my father saw this phenomenon as an example of the wisdom of nature that is inherent in all living systems, so that he would think of the slowing of growth as happening in response to the approach of limits to ensure survival and continued evolution,” he says.

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Unlike the single-species growth tests involving fruit flies or yeast cells, humankind is currently running a multispecies experiment with alarming consequences for non-human life. According to Salk, population growth and decline are in constant flux in the natural world and there are many possibilities in the shape of species’ growth curves. “If a species does not become extinct, but stabilizes at a new, lower, population level, that portion of the curve would be a reverse sigmoid,” he says. Salk argues that we can combat the current rapid biodiversity loss and encourage the growth of endangered species most effectively by limiting climate change. “If we can do that, a significant part of human life will be the care and respect for the natural, non-human world, the preservation of which is intimately tied to our survival,” he adds.

What about the ways technological development—and by extension, architecture—might influence Epoch B? According to Salk, although new technologies did spur the growth in Epoch A, they can also be a part of the adaptation to equilibrium and plateau in Epoch B—as well as the integration of Epoch B values into our daily lives. For example, technology can facilitate the reemergence of a sense of community and connection that declined during the period of accelerating growth. Furthermore, new approaches to harnessing renewable energy and extracting carbon from the atmosphere might facilitate, rather than exacerbate, the tapering of growth. Salk believes that “there will be some other advance in technology that will fuel further change such that even if we are at a plateau, in terms of population size and resource use, there will continue to be growth, change and evolution in the technological realm, and also in the human and creative realm.”

In A New Reality, the Salk paradigm transforms the Malthusian calamity into a situation where humans can exert some control. Unlike the predictable laboratory models of other species’ growth patterns, human technologies and behaviors are differentiating factors, and they can help shape our future path. According to Salk, “Adapting and changing our values, strategies and behavior now require urgent, radical and conscious human effort in order for us to survive.” Environmentally conscious technological development is also an essential element in our adaptation to Epoch B, he adds: “Given our sheer numbers and the ecological challenges that face us, our lives will depend on it.”