Physics / Experiment Review

Vol. 7, NO. 3 / December 2022

Planetary Intelligence

Charles Lineweaver

Letters to the Editors

In response to “Planetary Intelligence

Adam Frank, David Grinspoon, and Sara Walker, “Intelligence as a Planetary Scale Process,” International Journal of Astrobiology 21, no. 2 (2022): 47–61, doi:10.1017/S147355042100029X.

How did we get here? How do we compare to other life forms? Are we alone in the universe?1 Astronomy seems like an obvious place to seek answers to these questions. But compared to the enormity of astronomical space and time, our lives can seem short, small, and meaningless.2 An antidote to this malaise is Carl Sagan’s vision of an open-ended, enduring technological future for humanity3—a future in which we wake up and find out we are the eyes of the world.4 Adam Frank et al.’s paper “Intelligence as a Planetary Scale Process” (hereafter FGW) makes a provocative contribution to such narratives in which humanity plays a leading role.

But before we can reach our potential as a species, we find ourselves at a tipping point.5 Will we, in our selfish immaturity, continue to pillage and ruin the Earth, eventually leading to our extinction? Or, will we reverse our exploitative relationship with the Earth and become, as FGW suggest, the brain of the biosphere—the stewards of a mature and sustainable technosphere?6 FGW not only suggest that our current immature technosphere is facing an existential challenge, they also speculate that if exocivilizations exist on distant exoplanets, these societies may also be similarly challenged on their way to technospheric maturity.7

In order to survive this crisis, the authors suggest that humanity needs to acquire more maturity and intelligence. FGW begin by pointing out that although intelligence has conventionally been applied to individual organisms, there is much evidence for collective intelligence to be found among quorum sensing bacteria, bee hives, fungal networks, and eusocial animals, to name just a few examples. Thus, the concept of intelligence can be broadened from something an individual has to something a group can have. FGW go even further and argue that intelligence is something the entire biosphere could possess, and that the same could also be true for the biospheres of other exocivilizations—if they exist. Under these assumptions, the authors ponder whether the Earth is indeed smart, concluding that: “Even though Earth might be full of intelligent life, at this point in its cosmic history, it certainly doesn’t seem very smart.”8 Artificial intelligence, nuclear weapons, biotechnology, and climate change threaten our existence. We are eroding natural resources, changing the climate, ravaging the biosphere, and driving many species to extinction.9 All these are problems of our own making, and mitigating them is the central issue of our time.10

The Gaia hypothesis plays an important role in FGW’s vision of planetary intelligence. This is the idea that the Earth can be usefully viewed as a living organism, Gaia, with its own planetary physiology.11 Not content with this conception of Gaia, the authors ask: “If a planet with life has a life of its own, can it also have a mind of its own?” Indeed, FGW are seeking to improve upon the original notion of Gaia by making her more intelligent. The authors want to give her a brain and propose that if we humans can stay alive, we are destined to be that brain.

Human intelligence, or intelligence of any kind, has not played a significant role in the various versions of the Gaia hypothesis.12 Thus, giving Gaia a brain is an interesting new development. Not content with only our Gaian biosphere being intelligent, FGW also postulate the existence of Gaian biospheres on other Earth-like planets and argue that the concept of planetary intelligence will be “a useful framework for understanding and predicting the possible paths of the long-term evolution of inhabited planets.”

The authors propose that the evolution of planets like the Earth follows a linear chronological sequence. Such planets start as a geosphere without life. Then the emergence of life creates an immature biosphere, which then evolves into a mature biosphere. The next step is the evolution of an intelligent species, such as Homo sapiens, who produce an immature technosphere. This is the stage where Earth finds itself today, in the midst of an unsustainable Anthropocene crisis. Finally, if an intelligent species, such as ourselves, can mature into a trustworthy steward of a sustainable biosphere, the planet will evolve into a mature technosphere.13

This sequence postulates two potential branches in humanity’s future. One branch leads to human extinction; the other leads to a mature technosphere. We are afraid of branch one and hope for branch two. Yet the notion of maturity as a culmination for our species seems incongruous. Maturity without senescence or death implies that human technology—after shifting from unsustainable to sustainable—will have an enduring, open-ended future. But doctors and biologists agree that after maturity comes senescence and death. The same is true for species. New immature species evolve into mature species and across timescales that span tens of millions of years, they eventually disappear—either because they go extinct, or because they have evolved and diverged into different species. If we manage to avoid extinction, we will evolve into something so different from our present condition that we will no longer be human in any sense we now value.

Ignoring senescence is one problem. Another is that the history of defining and measuring human intelligence is a long-running tale of woe in which Social Darwinism, sexism, racism, and eugenics have all featured prominently.14 Indeed, the comparison between human intelligence and the intelligence of other species is plagued with unacknowledged speciesism and characterized by self-serving logic: human-intelligence is the best. It is the standard. Therefore, species possessing an intelligence most similar to our own are the smartest. Chimps are smarter than dogs. Placental mammals are smarter than marsupials. Eusocial organisms are more intelligent than nonsocial organisms. Animals are smarter than plants. Multicellular organisms are smarter than unicellular organisms. And eukaryotes are smarter than prokaryotes.15 Such systematic speciesism, genusism, and kingdomism is the propagation of familiar systematic prejudices at the subspecies level to larger cladistic levels.

Even more challenging are attempts to measure intelligence at different levels of organization. Which ecosystems are more intelligent? Jungles or savannah? Deserts or tundra? Assessing the relative intelligence of biospheres is even more baffling. Is an atmosphere with oxygen smarter than one without? Is Earth smarter than Krypton? There are so many different ways of making a living, so many different adaptive behaviors, so many different ways of acting intelligently and staying alive, that to reduce such n-dimensional diversity onto a one-dimensional scale of intelligence is an unhelpful impoverishment.

There is also an intrinsic contradiction between the notions of human exceptionalism and human stewardship of the Earth. Rather than helping us become better earthlings, the power of human intelligence and technology seems to be making us more arrogant and dismissive of other animals and the rest of the biosphere. Self-preserving behavior has been deeply integrated into the ethical circuitry of our brains. Can humans evolve and learn to act for the benefit of other species besides our own? Even if we are able to enlarge our circle of empathy to include all humans,16 what about the rest of the biosphere? Currently, we only take care of the biosphere to the extent that it benefits us. This is the human–biosphere alignment problem that FGW and environmentalists of all stripes are anxious to resolve in order to make our civilization sustainable.17 The perplexing part of this problem is that we are the only reason the biosphere needs saving. Are we supposed to save it from ourselves?18

Perhaps the strongest evidence against planetary evolution resulting in a long-lasting mature technosphere is what Paul Davies has described as “the eerie silence”19—the lack of any evidence for technological intelligences elsewhere in the universe; no radio messages, no Dyson spheres, no self-replicating robots, and no technosignatures.20 If mature technospheres evolve across the universe and endure for billions of years, then where are they?

Most of the community involved with the search for extraterrestrial intelligence believe that the reason we have not found any signs of life elsewhere in the universe is simply because we have not looked hard enough.21 They argue that if you take a bucket of water from the ocean and do not find any fish, this does not mean there are no fish in the ocean. But, if you take a bucket of water from the ocean and find no viruses, that is fairly good evidence there are no viruses in the ocean. Thus, the interpretation of the eerie silence depends on expectations. Are exocivilizations more like isolated fish and confined to their planetary system of origin? Or would they instead be more like viruses—spreading everywhere once they become capable of interstellar travel? In the latter case, absence of evidence is evidence of absence.22

Since the entire span of human civilization only stretches back a mere 10,000 years into the four-billion-year-history of our planet, and technological civilization occupies just the last few hundred years, it seems quite speculative to claim a mature technosphere as an enduring culmination of our future. And it seems even more speculative to claim that mature technospheres are what biospheres elsewhere evolve into. FGW seem to be aware of how speculative their proposal is, describing it as “an exploration of an exploration of planetary intelligence.” They hope that by pointing out the destructive immaturity of our current technosphere we will recognize our immaturity, reform ourselves, and become the mature stewards of a mature technosphere. They hope that this recognition will make us better earthlings and help us solve the current crises. To this reader they have produced an adaptive useful fiction—a myth that humanity may need to survive.23 If this Gaian-inspired planetary perspective on the future of humanity succeeds in inspiring us to protect the future of the biosphere, the authors should be proud of their redemptive narrative.


  1. See, for example, the Bible; Charles Darwin, The Origin of Species by means of Natural Selection (London: John Murray,1859); Charles Darwin, The Descent of Man and Selection in Relation to Sex, 1871; Thomas Huxley, Evidence as to Man’s Place in Nature (London: Williams and Norgate 1863); Alfred Russel Wallace, Man’s Place in the Universe (London: Chapman Hall, 1904); Jacob Bronowski, The Ascent of Man (Boston: Little, Brown and Company, 1973); Richard Dawkins, The Selfish Gene (Oxford: Oxford University Press, 1976); John Maynard Smith and Eors Szathmary, The Major Transitions in Evolution (Oxford: Oxford University Press, 1995); Noah Yuval Harari, Sapiens: A Brief History of Humankind (New York: HarperCollins, 2015); David Christian, Big History (London: DK Publishing, 2016). 
  2. Steven Weinberg observed that:
    It is almost irresistible for humans to believe that we have some special relation to the universe, that human life is not just a more-or-less farcical outcome of a chain of accidents reaching back to the first three minutes, but that we were somehow built in from the beginning ... It is very hard to realize that this is all just a tiny part of an overwhelmingly hostile universe. It is even harder to realize that this present universe has evolved from an unspeakably unfamiliar early condition, and faces a future extinction of endless cold or intolerable heat. The more the universe seems comprehensible, the more it also seems pointless.
    Steven Weinberg, The First Three Minutes: A Modern View of the Origin of the Universe, 2nd edn. (New York: Basic Books, 1993), 154; Sean Carroll, The Big Picture: On the Origins of Life, Meaning, and the Universe Itself (New York: Dutton, 2016). 
  3. Carl Sagan, The Cosmic Connection: An Extraterrestrial Perspective (New York: Double Day, 1973); Carl Sagan, Pale Blue Dot: A Vision of the Human Future in Space, (New York: Ballantine Books, 1994). 
  4. Grateful Dead song “Eye of the World” in 1973 album Wake of the Flood; see also David Grinspoon, Earth in Human Hands: Shaping Our Planet’s Future (New York: Grand Central Publishing, 2016). 
  5. Johan Rockström et al., “Planetary Boundaries: Exploring the Safe Operating Space for Humanity,” Ecology and Society 14, no. 32 (2009); Toby Ord, The Precipice: Existential Risk and the Future of Humanity (London: Bloomsbury, 2020). 
  6. The authors summarize their thesis in: Adam Frank, Sara Walker, and David Grinspoon, “Is Earth Smart?,” The Atlantic, February 19, 2022. 
  7. Aditya Chopra and Charles Lineweaver proposed a bottleneck much earlier in the evolution of life on a planet. See “The Case for a Gaian Bottleneck: The Biology of Habitability,” Astrobiology 16, no. 1 (2016): 7–22, doi:10.1089/ast.2015.1387. 
  8. Frank et al., “Is Earth Smart?.” 
  9. Nick Bostrom and Milan Ćirković, Global Catastrophic Risks (Oxford: Oxford University Press, 2008). 
  10. In The Precipice, Ord estimates that anthropogenic risks are 30 times larger than natural ones (e.g. asteroid impacts and super-volcanoes). Recently founded institutions addressing these problems include: Future of Humanity Institute at Oxford University, Future of Life Institute, and Earth Futures Institute; See also Harari Sapiens; Noah Yuval Harari, Homo Deus: A Brief History of Tomorrow, (New York: HarperCollins 2017); Noah Yuval Harari, 21 Lessons for the 21st Century (London: Jonathan Cape, 2018); David Christian, Future Stories: What’s Next? (Boston: Little, Brown Spark, 2022); Nick Bostrom, Superintelligence: Paths, Dangers, Strategies (Oxford: Oxford University Press, 2014); Max Tegmark, Life 3.0: Being Human in the Age of Artificial Intelligence (New York: Knopf, 2017). 
  11. The Gaia Hypothesis is the idea that the biosphere has a life and body of its own with a physiology, circulatory systems based on global scale biogeochemistry, feedback loops, bacterial emissions and oxygenic photosynthesis. To trace the development of the Gaia hypothesis, see Vladimir Vernadsky, The Biosphere (New York: Springer, 1998; translation of Biosfera Leningrad, Nauka: 1926); James Lovelock and Lynn Margulis, “Atmospheric Homeostasis by and for the Biosphere: The Gaia Hypothesis,” Tellus XXVI 1–2 (1974); James Lovelock, Gaia: A New Look at Life on Earth (Oxford: Oxford University Press, 1979); James Lovelock, “What is Gaia?,” Trends in Biochemical Sciences 9, no. 74 (1984); Timothy Lenton, “Gaia and Natural Selection,” Nature 394 (1998): 439–47, doi:10.1038/28792; Timothy Lenton and Andrew Watson, Revolutions That Made the Earth (Oxford: Oxford University Press, 2011). For critical reviews of the Gaia Hypothesis see Richard Dawkins The Extended Phenotype (Oxford: Oxford University Press, 1982), 235–6; Stephen Schneider and Penelope Boston, Scientists on Gaia (Cambridge, MA: MIT Press, 1991); Stephen Schneider et al., Scientists Debate Gaia: The Next Century (Cambridge, MA: MIT Press, 2004); Michael Ruse, The Gaia Hypothesis: Science on a Pagan Planet (Chicago: University of Chicago Press, 2013); Toby Tyrrell, On Gaia: A Critical Investigation of the Relationship between Life and Earth (Princeton, NJ: Princeton University Press, 2013). 
  12. In the following quotes, one can see the relative unimportance of the human mind in the Gaia of Lynn Margulis and Dorion Sagan.
    Perhaps the greatest psychological stumbling block in the way of widespread scholarly acceptance of Gaia is the implicit shadow of doubt it throws over the concept of the uniqueness of humanity in nature. Gaia denies the sanctity of human attributes. If intricate planning, for instance can be mimicked by cunning arrays of subvisible entities, what is so special about Homo sapiens and our most prized congenital possession, the human intellect? The Gaian answer to this is probably that nothing is so very special about the human species or mind. … [H]uman beings, in spite of our raging anthropocentrism, are relegated to a tiny unessential part of the Gaian system. People, like Brontosaurus and grasslands, are merely one of the many weedy components of an enormous living system dominated by microbes.
    Lynn Margulis and Dorion Sagan, Slanted Truths: Essays on Gaia, Symbiosis and Evolution (New York: Copernicus, 1997), 155–56.
    On the other hand, in this quote Margulis and Sagan seem to foreshadow the idea of humans as the future brain of Gaia:
    …our ultimate potential as a nervous early warning system for Gaia remains unsurpassed. Deflecting oncoming asteroids into space and spearheading the colonization of life on other planets represent additions to the Gaian repertoire that our species must initiate.
    Margulis and Sagan, Slanted Truths, 157. 
  13. This narrative is illustrated in Figures 1, 2, 3 and 5 of their paper.  Other linear narrative evolutionary scenarios have been proposed: Nikolai Kardeshev, “Transmission of Information by Extraterrestrial Civilizations,” Soviet Astronomy 8 (1964): 217–21; and Eric Chaisson, “The Natural Science Underlying Big History,” The Scientific World Journal (2014), doi:10.1155.2014/384912. In The Singularity is Near: When Humans Transcend Biology (New York: Viking, 2005), Ray Kurzweil proposed six epochs. The four epochs which have occurred so far are Physics and Chemistry, Biology and DNA, Brains, and Technology. The Singularity will coincide with the next epoch when there will be the Merger of Human Technology with Human Intelligence. After the Singularity during the final epoch, the Universe Wakes Up. Intelligence will then radiate outward from the planet until it saturates the universe. See also David Christian, Maps of Time: An Introduction to Big History (Berkeley: University of California Press, 2004). During TED talks in 2011 and 2012, Christian proposes eight thresholds in a narrative of Big History: Big Bang, Stars, Elements, Planets, Life, Humans, Civilizations, Industry. Presumably these scenarios are relevant to only the Earth. See David Christian, “The History of Our World in 18 Minutes,” YouTube video, April 11, 2011; and David Christian, “The Stages in Big History,” YouTube video, May 23, 2012. In a 2018 paper, Hikaru Furukawa and Sara Walker extrapolate three epochs to all planets: “We can classify these evolutionary stages of planets into matter-dominated, life-dominated, and agency-dominated phases, where each is distinguished by the extent to which information processing systems control planetary processes.” Hikaru Furukawa and Sara Walker, “Major Transitions in Planetary Evolution,” Artificial Life Conference Proceedings. Cambridge: MIT Press, (2018), 101–2. 
  14. See Stephen Gould, Mismeasure of Man, (New York: Norton, 1996) and his critique of Richard Herrnstein and Charles Murray, The Bell Curve: Intelligence and Class Structure in American Life (New York: Free Press, 1994). Gould argues that for hundreds of years questionable measurements of human intelligence, like skull size or IQ, have been used to justify racism, sexism, and class stratification:
    one number for each individual, and the use of these numbers to rank people in a single series of worthiness, invariably to find that oppressed and disadvantaged groups—races, classes, or sexes—are innately inferior and deserve their status.
  15. Lori Marino, “Objectivity in the Study of Intelligence: The Cornerstone of New Methods and Discoveries,” Bioastronomy 2002: Life Among the Stars, IAU Symposium, vol. 213, eds. R. P. Norris and F. H. Stootman, (2004); Charles Lineweaver, “Paleontological Tests: Human-like Intelligence is not a Convergent Feature of Evolution,” in From Fossils to Astrobiology: Records of Life on Earth and the Search for Extraterrestrial Biosignatures, eds. Joseph Seckbach and Maud Walsh (Berlin: Springer Science+Business Media, 2008), 353–68, doi: 10.1007/978-1-4020-8837-7_17. 
  16. Peter Singer, The Expanding Circle: Ethics and Sociobiology (Oxford: Clarendon Press, 1981). 
  17. Adam Frank, David Grinspoon, and Sara Walker, “Intelligence as a Planetary Scale Process,” International Journal of Astrobiology 21, no. 2 (2022): 47–61, doi:10.1017/S147355042100029X. 
  18. The wisdom of traditional societies could be invoked as evidence that humans can be good stewards of the Earth. But it is easy not to threaten the biosphere if human technology is practiced by a small population kept small by disease, infant mortality, and tribal warfare. Jared Diamond, Collapse: How Societies Choose to Fail or Succeed (New York: Viking, 2005); and Jared Diamond, The World Until Yesterday: What we can learn from Traditional Societies (New York: Viking 2012). 
  19. Paul Davies, The Eerie Silence (New York: Houghton Mifflin Harcourt, 2010); and Michael Hart, “An Explanation for the Absence of Extraterrestrials on Earth,” Quarterly Journal of the Royal Astronomical Society 16 (1975): 128–35. Hart calls the eerie silence “Fact A” 
  20. Jason Wright et al., “The Case for Technosignatures: Why They May Be Abundant, Long-lived, Highly Detectable, and Unambiguous,” The Astrophysical Journal Letters 927. No. 2  (2022), doi:10.3847/2041-8213/ac5824. 
  21. Seth Shostak, Confessions of an Alien Hunter: A Scientist’s Search for Extraterrestrial Intelligence (National Geographic, 2009); Jason Wright et al., “How Much SETI Has Been Done? Finding Needles in the n-dimensional Cosmic Haystack,” The Astronomical Journal, 156, no. 6 (2018): 260, doi:10.3847/1538-3881/aae099; and Silicon Valley Astronomy Lectures, “A Little Talk About Aliens: Techno-Signatures and the new Science of Life in the Universe [Adam Frank],” YouTube video, May 28, 2021. 
  22. Hart, “An Explanation for the Absence of Extraterrestrials on Earth”; Frank Tipler, “Extraterrestrial Intelligent Beings Do Not Exist,” Quarterly Journal of the Royal Astronomical Society 21 (1980): 267–81; Keith Wiley, “The Fermi Paradox, Self-Replicating Probes, and the Interstellar Transportation Bandwidth,” arXiv:1111.6131; and Charles Lineweaver, “A Lonely Universe,” Inference 6, no. 4 (2022), doi:10.37282/991819.22.11; but see Carl Sagan and William Newman, “The Solipsist Approach to Extraterrestrial Intelligence,” Quarterly Journal of the Royal Astronomical Society 24 (1983): 113–21; Glen Brin, “The ‘Great Silence’: The Controversy Concerning Extraterrestrial Intelligence,” Quarterly Journal of the Royal Astronomical Society 24 (1983): 283–309; and Milan Ćirković, “Fermi’s Paradox—The Last Challenge for Copernicanism?,” Serbian Astronomical Journal 178 (2009):1–20. 
  23. Harari, Sapiens; Charles Lineweaver, “Cosmic Perspectives and the Myths we need to Survive,” Journal of Big History, III(3) (2019): 81–93, doi:10.22339/jbh.v3i3.3350. 

Charles Lineweaver is an Associate Professor at the Research School of Astronomy and Astrophysics at the Australian National University.

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