Technological innovations have allowed exponential growth in the human population and economy, but can it continue? A new model combining population, culture, and innovation projects possible futures for humanity.
Humans are a peculiar species. On the one hand, we’re vulnerable to the same environmental constraints, such as food shortages and disease, that keep all species in check. On the other hand, there is no question that Homo sapiens is extraordinarily successful. In just 10,000 years, we have gone from small networks of hunters and gatherers using simple tools to hyper-dense agglomerations in technologically rich cities1. From the axe to the modern power grid, innovations have allowed the human system (population and economy) to grow, produce new technologies, and grow more. Whether these trends will continue is a hotly contested question that historically divides disciplines such as ecology and economics. In a special issue on innovations in Philosophical Transactions B, Weinberger and colleagues propose a new model to bridge this academic divide by linking the dynamic feedbacks between human population growth and the ecosystem services that support it through the process of cumulative cultural evolution (CCE)2.
Such CCE is the accumulation of socially-learned technologies — technologies that are tried, transmitted, modified, and recombined over time through copying, teaching, and learning3,4. CCE is undoubtedly a distinguishing characteristic of the human species5, and understanding it may provide novel insights into humanity’s predicament. By promoting innovations that draw ever more food, water, fuel, and other ecosystem services into the human system, CCE has enabled us to live in more places on Earth and use a wider variety of resources, effectively expanding the human niche.
The model by Weinberger et al. highlights the particular role human population size plays in enhancing cultural evolution and driving technological innovation. In the model, CCE drives technological innovations aimed at increasing the flow of energy, materials, and other ecosystem services from the finite biosphere to the embedded human system (Fig. 1). Maintaining growth in the human system depends on the net effects of technological innovations on the flow of ecosystem services and on future technologies. The net effects are key because some technologies will have negative impacts on ecosystem services, such as depletion of non-renewable resources, as well as positive impacts on future technologies, such as by enabling use of cleaner energy sources.
Critically, if the feedback from technological innovation is too small, the human system will collapse due to runaway growth that exceeds the flow of ecosystem services6. However, if technology enhances creation of those innovations needed to keep pace with a growing human system (that is, large technological feedback), then collapse may be avoided. The model thus shows that a technological innovation can degrade ecosystem services today yet still sustain human society long-term if the technological feedback generates less-harmful future technologies. A technological innovation that allows full substitution of renewables for fossil fuels would be an example.
The Weinberger et al. model deepens our understanding of the critical thresholds upon which humanity precariously sits. While the relationship among resource use, population, and innovation has received considerable attention from past scholars (for example, Ester Boserup, Leslie White, Fred Cottrell, Howard Odum, Herman Daly, Paul and Anne Ehrlich, and The Club of Rome), this new model makes an earnest attempt to unite the dynamic processes of ecology, demography, culture, and technology that underpin human society into a deliberately simple mathematical form. However, the human–environment interface is complex, with feedback relationships that could result in rapid collapse. Future research should estimate the 18 model parameters using real data, both across the globe and through human history, to assign likelihoods to different scenarios.
In the end, what is the likelihood that technology will outpace collapse? The start of the Anthropocene has been marked as the point in history when humans began tapping into energy sources stored on geological time scales (~300 million years ago) in the form of fossil fuels7. The scientific evidence is clear that the rapid discharge of the Earth’s stored biomass (such as in plants and animals) and fossil energy to fuel a growing human system is having alarming impacts on climate, biodiversity, and physical geography8. Contrary to expectations, technologies that increase efficiency often accelerate resource consumption instead of promoting resource conservation (the rebound effect, or Jevons paradox9). If innovations make coal cheaper, we tend to use more of it, swamping any benefit from the innovations. This illuminates the challenge for technology to keep pace with accelerating trends in resource consumption.
The Weinberger et al. model refines what is perhaps the most important question for humankind — will technology outpace environmental constraints and prevent collapse of the human population and globalized economy? The model produces different scenarios for how the future of humanity may play out. A fruitful way forward is to understand the rates of cultural and technological innovation and the necessary feedbacks for transitioning to renewable energy in a post-fossil-fuel era. A useful analytical tool is the notion of energy return on investment (EROI), meaning the ratio of usable energy derived from a resource to the amount of energy used to obtain it (sensu 10). The EROI provides a powerful currency to evaluate the likelihoods of the different scenarios revealed by the Weinberger et al. model. Quantifying the EROI required to substitute renewables for fossil fuels will foretell just how colossal a task innovating fast enough to outpace collapse may be. The new model by Weinberger and colleagues clarifies the mechanics that underlie humanity’s predicament.