Sara Walker is an astrobiologist and theoretical physicist. She is the deputy director of the Beyond Center for Fundamental Concepts in Science and a professor in the School of Earth and Space Exploration at Arizona State University; external faculty at the Santa Fe Institute; and a fellow at the Berggruen Institute.
Toward the end of August 1924, the orbits of Mars and Earth carried the two sister planets closer to each other than they had been in around a century. Enthusiasm for the event spread across the United States. An article in the New York Times anticipated that astronomers “may definitively solve the question whether Mars is inhabited.” The government requested five minutes of complete radio silence, on the hour every hour, across the nation over the days when the planets were closest to one another, with the hope that this radio silence would increase our chance of detecting any signals broadcast by Martians.
No message came.
As long as we have looked toward worlds that might be among the stars, we have hoped for and assumed life would be on them. Disappointment and shock greeted the news that there was no observable life revealed by the first images of the surface of Mars. Since then, we have grown accustomed to images of other barren worlds in the decades.
But could we recognize life if it is really out there? We are embedded in a living world, yet we do not even recognize all the life on our own Earth.
For most of human history, we were unaware of the legions of bacteria living and dying across the surface of everything in our environment — even within us. It took the technological innovation of the microscope in the late 16th century for us to finally see a microscopic world teeming with life. The first indication we had of viruses was cryptic patterns in infectious diseases they cause, but their existence was only confirmed in the late 19th century. We also did not know about the ecosystems thriving near hydrothermal vents in the darkest depths of the ocean floor until the second half of the 20th century, when submarines that could stand intense pressures got us close enough to observe them.
The discovery of new forms of life requires the advent of technologies that allow us to sense and explore the world in new ways. But almost never do we consider those technologies themselves as life. A microbe is life, and surely a microscope is not. Right? But what is the difference between technology and life? Artificial intelligences like large language models, robots that look eerily human or act indistinguishably from animals, computers derived from biological parts — the boundary between life and technology is becoming blurry.
A world in which machines acquire sufficient intelligence to replace biological life is the stuff of nightmares. But this fear of the artificiality of technology misses the potentially far-reaching role technologies may play in the evolutionary trajectories of living worlds.
Complex (technological) objects do not just appear spontaneously in the universe, despite popular folklore to the contrary. Cells, dogs, trees, computers, you and I all require evolution and selection along a lineage to generate the information necessary to exist.
Here on planet Earth, this is evident even in the rocks: Mineral diversity has co-evolved with life, for example through the process of biomineralization, in which organisms produce minerals to strengthen shells or skeletons or accomplish some other goal. The global rock record literally includes the fossilized remains of the history of life, because life has altered the geosphere so markedly. Because of this, we expect worlds with no life will have different compositions than the Earth does, even in the nonliving materials that compose them.
Many of us would not recognize mineral diversity as “life” any more than we would the computer screen or magazine you are reading this text on as “life,” but these are products of a sequence of evolutionary events enacted only on Earth. This is as true for a raven as it is for a large language model like ChatGPT. Both are products of several billion years of selective adaptation: Ravens wouldn’t exist without dinosaurs and the evolution of wings and feathers, and ChatGPT wouldn’t exist without the evolutionary divergence of the human lineage from apes, where humans went on to develop language.
Attempts to define life have so far failed because they focus on containing the concept of life in terms of individuals rather than evolutionary lineages. Invariably, something is included or excluded from the category of “living” that probably should not be. If you draw the line at self-reproducing or self-sustaining, viruses or parasites are excluded. (Viruses are often cited as a boundary case for exactly this reason.) If you draw the line based on the consumption of energy, fire can reasonably make the cut. Other definitions face similar problems. A popular one first developed by a NASA working group — “life is a self-sustaining chemical system capable of Darwinian evolution” — at first seems innocuous enough. But on closer conceptual inspection, it faces these same pitfalls. Only populations evolve — individuals do not. And it raises a question rather than providing an answer: Must all life rely on chemical reactions to exist?
To move beyond these circular debates, we need to get past our binary categorization of all things as either “life” or “not.” We should not exclude examples based on naive assumptions about what life is before we develop an understanding of the deeper structure underlying the phenomena we colloquially call “life.”
Consider the discovery of the nature of motion. When physicists talk about motion, the details of different examples of moving things are of no concern. Color, size, texture, age — none of that is important for calculating how objects move through space. We only care about mass, position and velocity (plus derivatives). Realizing that moving things can be described in terms of just a few observables was a huge conceptual leap made by our species. In the words of Isaac Asimov, “We all know we fall. Newton’s discovery was that the moon falls, too — and by the same rule that we do.”
All motion, whether here on Earth or on the other side of the observable universe, can be described in the same way. This discovery — this development of the laws that form the abstract description of motion — unified what happens terrestrially with what happens celestially. Before we understood motion at such a level of depth and abstraction, we had no idea the heavens were governed by the same laws as the Earth.
Just as our ancient ancestors could not have expected the same rules governing motion here on Earth to also apply to the heavens, a deep abstract structure underlying life need not conform to our current expectations. While there are many features of life that may be observed across many examples, such as replication or metabolism, these are not entirely universal — each has exceptions.
In the search for a deep abstract mathematical framework that explains life, we are looking for the features we expect all life in the universe to share, whether it is here on Earth or anywhere else in the universe we might find it. Once we developed universal laws for motion, we were able to predict properties of moving objects we have not yet observed. In the same way, if we identify the “laws of life,” we should be able to predict the properties of alien examples. And just as with motion, we will have to ignore many details to get at a more universal and therefore deeper understanding.
Our best estimates place the origin of life on this planet at approximately 3.8 billion years ago. Biological beings alive today are part of a lineage of information that can be traced backward in time through genomes to the earliest life. But evolution produced information that is not just genomic. Evolution produced everything around us, including things not traditionally considered “life.” Human technology would not exist without humans, so it is therefore part of the same ancient lineage of information that emerged with the origin of life.
Technology, like biology, does not exist in the absence of evolution. Technology is not artificially replacing life — it is life.
It is important to separate what is meant by “life” here as distinct from “alive.” By “life,” I mean all objects that can only be produced in our universe through a process of evolution and selection. Being “alive,” by contrast, is the active implementation of the dynamics of evolution and selection. Some objects — like a dead cat — are representative of “life” (because they only emerge in the universe through evolution) but not themselves “alive.”
To understand life may therefore require us to unify the biological and technological, akin to how the celestial and terrestrial were unified in our explanations for motion.
The canonical definition of technology is the application of scientific knowledge for practical use. Historically, where philosophy and technology intersect, the goal has been to apply old philosophical ideas to understand new technology. However, as the philosopher of mind David Chalmers has pointed out, in the area of techno-philosophy, this logic can be inverted: Technology can be used as a new lens with which to visit old questions in philosophy.
We can also ask what new insights might be gained by taking a broader, non-human-centric view of what constitutes technology and how this can be used to reinvestigate old questions in philosophy and biology alike. Technology relies on scientific knowledge, but scientific knowledge is itself information that emerged in our biosphere. It enables things to be possible that would not be without it.
Consider satellites. Launching them into space would not have been possible on our planet without Newton’s invention of the laws of gravitation. Newton himself could not have invented those laws if, centuries earlier, humanity had not come to understand the mathematics of geometry or constructed timekeeping devices that allowed us to track seconds. And of course, none of this could have happened if our biosphere had not evolved organisms capable of making abstractions like these in the first place.
Once the knowledge of laws of gravitation became encoded in our biosphere, new technologies were made possible, including satellites. Satellites are not launched from dead worlds or worlds with only microbial life. They require a longer evolutionary trajectory of information acquisition. You can trace that lineage within the history of our species, but arguably it should be traced all the way back to the origin of life on Earth.
Technology, in the broadest sense, is the application of knowledge (information selected over time) that allows things to be possible that are not possible in the absence of that knowledge. In effect, technologies emerge from what has been selected to exist. They are also what selects among possible futures — and builds them. Consider robust carbon removal technology, which could change the future evolutionary trajectory not just of humans but of a huge diversity of species on Earth.
We are accustomed to thinking about technology as uniquely human, but in this broader definition, there are many examples across the biological realm. Just like the objects of life might include pencils and satellites, so too technology might include wings and DNA translation. Photosystems I and II — multiprotein complexes found in plants and other photosynthesizing creatures — harvest photons to use light energy to catalyze reactions. As evolutionary innovations, these technologies radically changed the climate of Earth in the Great Oxidation Event, a period about 2.5 billion years ago when cyanobacteria produced a great deal of atmospheric oxygen, which contributed to later conditions supportive of multicellular life.
People might want to differentiate between biological evolution and the intentionality of humans when we build technologies. After all, software developers and companies choose to produce technology in a different way than ravens evolved wings to fly. But both fundamentally rely on the same principles of selection.
Arguably, the kind of selection humans do is much more efficient than natural selection on biological populations. It is more directed, which is only possible because we ourselves already are structures built across billions of years. We are bundles of possibilities refined by evolution and embodying the history of how we came to exist. The physics governing how we select what we create may be no different (other than by degree of directedness) than how we were selected by evolution. We are, after all, a manifestation of the very physics that allowed us to come to be.
Biological Innovations Are Technologies
Roughly 3.8 billion years ago, some of the most ancient technologies now on our planet were first invented. Among those is the chemistry of translation.
Translation allows information stored in the sequences of DNA to be read out by the translation system of the cell to produce specific protein sequences. A universal code — digitally encoded in the sequence of nucleobases — used by all organisms (with minor variations) had evolved that allowed genes from one organism to be shared with another and retain their meaning. This technology is so robust that it has persisted for almost 4 billion years and is part of nearly everything alive on this planet right now. No technology yet invented by humans will last that long, although if we come to understand what we are, something might.
Far earlier than humans, it was the biosphere that invented many technologies. Over billions of years, the innovations of sight and hearing, among many others, emerged through evolution and selection. We do not know exactly what the Earth looked like when life first emerged. In fact, neither did the life that existed at that time. Nothing alive then could see. The evolution of photon receptors and eventually eyes relied on many other innovations previously made over a great deal of time by single-cell organisms. Multicellular creatures like mammals, which rely on about 70 different specialized cells to see, further advanced the technology of sight, but only by building on what came before. The mantis shrimp evolved perhaps the most complex multicellular eye: It has compound eyes that move independently and have up to 16 color receptors (our eyes have three).
The history of life on Earth is full of new and better organisms developing technologies by innovating on what came earlier, all the way back to the deep history of ancient life. A key feature of life is this evolutionary contingency: New objects only come into existence because there is a history that supports their formation. Multicellular eyes could not evolve before cells with photon receptors any more than ChatGPT could evolve before human language — both rely on previous developments in a lineage of evolving technology.
The technologies we are and that we produce are part of the same ancient strand of information propagating through and structuring matter on our planet. This structure of information across time emerged with the origin of life on Earth. We are lineages, not individuals.
Human technologies are therefore not much different from other innovations produced in our planet’s 3.8-billion-year living history — with the exception that they are in our evolutionary future, not our past. Multicellular organisms evolved vision; what I will call “multisocietial aggregates” of humans evolved microscopes and telescopes, which are capable of seeing into the smallest and largest scales of our universe. Life seeing life. All of these innovations are based on trial and error and selection and evolution on past objects.
Intelligence is playing a larger role in modern technology, but that is to be expected — intelligence itself improves via evolution. It generates more complex systems — cells, multicellular aggregates like humans, societies, artificial intelligence and now multisocietial aggregates like international companies and groups that interact at the planetary scale. So-called “artificial intelligences” — large language models, computer vision, automated devices, robotics and more — are often discussed as disembodied and disengaged from any evolutionary context. But the technologies we are inventing today represent the recapitulation of life’s innovations into new substrates, and these are allowing the emergence of intelligent life at a new scale — the planetary. There is no “intelligence” in isolation; rather, complex ecosystems of technologies interact with biology to bring about new capabilities.
First came cells with photon receptors, then eyes, then microscopes and telescopes. Now, we are in the midst of another transition from the biological to technological: We are using algorithms to interpret data and “see” the world for us.
It is a bit like how brains had to co-evolve to process the information gathered by eyes. How we think is another innovation evolved over billions of years, which is just now being recapitulated at a larger scale than our individual brains. We need to evolve technologies to process the huge amounts of data we are receiving and generating so we can “see” the world as a planet.
The technology of computation first emerged from the brains of humans, which themselves evolved over billions of years, in an attempt to build a mathematical abstraction that captured the structure of human thought. Just as we outsource some of our sensory perceptions to technologies we built over centuries, we are now outsourcing some of the functioning of our own minds. This allows the same principles that operate within us to function now at higher levels of organization, moving up from localized societies to global ones.
AI Is A Major Transition In Planetary Evolution
James Lovelock and Lynn Margulis’s Gaia hypothesis — that living organisms interact with the Earth to produce a self-regulating complex system that maintains conditions favorable for life — is sometimes interpreted to mean that the Earth itself is alive. Margulis and Lovelock’s insight was to recognize that, over eons, living organisms (trees, for example) produce gases that affect the atmosphere, warming or cooling the surface of the Earth to keep it within a range conducive to life. Other researchers have noticed that, at certain times in Earth’s history (the human-driven warming of today’s climate crisis being the latest example), life has failed to maintain this careful balance, leading to large-scale extinctions.
But we have yet to conceptualize the implications of the Gaia hypothesis because we don’t yet understand what life is.
A challenge is that biological modes of evolution do not apply to biospheres. We do not yet fully understand what evolution is doing at the planetary scale. We do know that the history of individual organisms within the biosphere has gone from the simple to the more complex (though not the case along every lineage). Prokaryotes are “simple” — mostly single-celled life with no internal organelles within them. “Complex” life evolved as cells became more structured, with components inside and out, allowing multicellular life and tissues with specific functions.
Individual multicellular systems then formed societies. In human societies, we went on to evolve language. As the evolutionary biologists Eörs Szathmáry and John Maynard Smith have pointed out, each of these major evolutionary transitions has been associated with new modes of information transfer and storage. The multisocietal aggregates that have only very recently emerged on this planet are made possible through the interaction of linguistic societies.
A natural extension of this evolutionary history is to recognize how “thinking” technologies may represent the next major transition in the planetary evolution of life on Earth. It is what we might expect as societies scale up and become more complex, just as life simpler than us has done in the past. The functional capabilities of a society have their deepest roots in ancient life, a lineage of information that propagates through physical materials. Just as a cell might evolve along a specific lineage into a multicellular structure (something that’s not inevitable but has happened independently on Earth at least 25 times), the emergence of artificial intelligences and planetary-scale data and computation can be seen as an evolutionary progression — a biosphere becoming a technosphere.
One example of planetary-scale computation is global monitoring of planetary health, if the data can be used to adaptively respond. Another example is large language models because they require the global integration of massive amounts of language data for their training.
The Gaia hypothesis was intended to conceptualize how life has established feedback loops with the planet that allow it to maintain itself over time. It did not address the hierarchy of complexity that life evolves over time — that is, the major transitions of life recurring across scales, from molecular to cellular, to multicellular to societal, to multisocietal to planetary.
If life is truly a planetary phenomenon, we should expect to see the same features recurring across time at new levels of organization as they gradually scale up to the planetary. What is emerging now on Earth is planetary-scale, multisocietal life with a new brain-like functionality capable of integrating many of the technologies we have been constructing as a species over millennia. It is hard for us to see this because it is ahead of us in evolutionary time, not behind us, and therefore is a structure much larger in time than we are. Furthermore, it is hard to see because we are accustomed to viewing life on the scale of a human lifespan, not in terms of the trajectory of a planet.
Life on this planet is very deeply embedded in time, and we as individuals are temporary instances of bundles of informational lineages. We are deeply human (going back 3.8 billion years to get here), and this is a critically important moment in the history of our planet but it is not the pinnacle of evolution. What our planet can generate may just be getting started. In all likelihood, we are already a few rungs down in the hierarchy of informational systems that might be considered “alive” on this planet right now.
We are 3.8-billion-year-old lineages of information structuring matter on our planet. We need to recognize our world teems with life and also that life is what we are evolving into. It is only when we understand ourselves in this context that we have any hope of recognizing whatever life, currently unimagined and evolving along radically different lineages, might exist, or we might generate to co-evolve with us.