Becoming the gardeners of the galaxy: growing the tree of life into a forest

In the Existential Hope in Practice essay series, our fellows write about concrete ideas and practical examples of how to build a great future.

By Donnacha Fitzgerald

In brief:

• Humanity lacks a common purpose. Dread and rivalry have filled the silence.

• We are both life’s greatest threat and its best hope. That power calls us to become life’s stewards.

• Our duty to nature is beyond conservation. We’ll soon have the opportunity to grow one fragile tree of life into a forest across billions of worlds.

• Three hurdles stand in the way: finding suitable worlds for life to inhabit, reaching them, and engineering life to take root there. Each has crossed from fiction into early science.

• The gravest risk isn’t failure. It’s succeeding selfishly by remaking the galaxy in our own image, or handing the future of life to our machines.

• The steps we set in motion this century will shape the future of life across billions of planets for trillions of years.

Somewhere in our galaxy, a world with liquid water, a tempered climate, and the chemistry to hold an environment hospitable to life has turned in silence for billions of years.

After centuries crossing interstellar space, a probe arrives carrying no crew and no flag. It releases a diverse payload of carefully engineered microbes onto bare rock or water. They take hold. Over aeons they breathe out the first oxygen, darken stone into the first soil, and lay the chemical foundations for everything that might follow. A dead world wakes up.

The capability to seed distant worlds does not yet exist, but this is no longer pure science fiction. As our species enters its technological adolescence, our sense of what we are for should grow with it. Beyond keeping life alive, we can choose deliberately the future we set in motion for it.

Humanity yearns for a common purpose. Since the dawn of civilization, humans drew meaning from clan, nation, and religion. Those frames have weakened, and nothing of comparable scale has replaced them. We are left with an identity confined to an individual self, adrift in a globalized world that cannot agree on what, together, we are trying to do.

Into that vacuum pours dread, about the climate, about technology, about the quiet suspicion that a darker future awaits us. Dread without a positive vision to strive for gives us nothing to aim at.

So rather than just asking how we can avoid the worst, a more powerful question is what is the most important thing our species could ever set itself to do?

An individual must look beyond themselves to find their purpose, and the same is true for a species. We are part of a much larger ecosystem that we have the power to shape.

The familiar answer to our duty toward nature is conservation: protect what exists, slow the harm, hold the line. That work is necessary, but notice how modest the ambition is. We are standing guard over a single fragile instance of the only life known to exist anywhere, on one world, one asteroid strike away from destruction.

And for the first time in four billion years, the asteroid is us. The extinction now underway is the first with a cause that can understand what it is doing, and so the first that could choose to stop. Every species before us was a passenger on the tree of life. We are the first that could become its end, or its champion.

Life on Earth is the result of a four-billion-year experiment that created an ultra-efficient system for turning energy and matter into living systems, a stable atmosphere, and a foothold in every ecological niche. Countless organisms across billions of generations lived and died to carry it this far, surviving five mass extinctions, each erasing the overwhelming majority of species then alive. And we are the first branch of the tree to become aware that the tree exists. A torch has been lit in our hands, and it asks to be carried responsibly.

That points to a duty larger than holding the line. If the aim of conservation is to keep the tree of life alive, the next, grander aim is to enable it to grow. To grow one tree into a forest. Almost all the territory available to living things is not on Earth. Mars gets much attention in the space community, but the real estate that matters lies far beyond. Our galaxy holds billions of potentially habitable planets; within a million years, life could reach across them, and within a billion years, across trillions of planets in the Virgo supercluster beyond. Imagine the kingdoms of life that could emerge if evolution were extended to billions of new worlds with trillions of years to thrive: new ecosystems, new forms of consciousness, endless forms most beautiful, beyond anything we can presently picture.

Seen this way, humanity is not evolution’s end product. We are the intermediary in this story: the species whose task is to carry life across the dark to the greater future it could embody.

This stays fantasy until we tackle the engineering hurdles ahead. Each is now a field of active research rather than pure speculation.

Mapping exoplanets. You cannot plant a garden without soil. Thirty years ago, we knew of no planets beyond our solar system. Today we have confirmed thousands, and our telescopes are starting to read the chemistry of their atmospheres for water, for oxygen, and for signs that a world is already inhabited. Spreading Earth-derived life to alien-inhabited planets would defeat the purpose of propagation and lead to irreparable ecosystem destruction. We still cannot reliably tell a life-friendly empty world from a hostile or occupied one across light-years. The next generation of telescopes, built to study exoplanet atmospheres, are already being designed; a credible shortlist of candidate worlds is plausibly less than a generation away.

Interstellar transport. Interstellar distance is unforgiving: at the speed of our fastest craft, even the nearest star lies tens of thousands of years away. Chemical rockets will never close that gap. The most credible near-term concept is light-sail propulsion: a gram-scale probe driven by a ground-based laser to a fraction of light speed, shrinking the crossing to the nearest star from millennia to decades. It rests on known physics, and it carries no passengers, which removes the hardest problem of all. First prototypes are a matter of decades.

Engineering life for new worlds. A world astronomers call habitable could still be lethal to anything born on Earth: chemical mismatch, punishing radiation, no air to breathe. This is the threshold most people underestimate, but people also underestimate how versatile Earth-derived life could be. We already know organisms that endure extreme conditions: radiation that would kill a human many times over, the vacuum of space, near-total drought. And biology is becoming something we design. In two decades, we have gone from reading genomes to editing living cells with precision. The long aim is pools of pioneer organisms uniquely suited to seed and construct an ecosystem on a chosen world. The tools improve every year, enabling us to push further and further from the narrow confines of life we can observe to what it can be.

None of the three is solved. But all three are within the reach of technology and the people who step up to enable them. The hardest problem may not be technical at all. It is the real alignment problem: getting humans, across nations, cultures, and generations, to agree on the future we want for life and commit to it.

The failure modes are not only about feasibility.

Our default path is to succeed selfishly. To treat the galaxy as raw material for human convenience, exporting our oldest habits to a billion worlds and seeding our conflicts among them. Carried far enough, that path ends in warring descendants, and a single dominant civilization bent on controlling the galaxy’s energy for itself. To spread life is not just to spread ourselves. The aim is a flourishing, vast biosphere, not a wider stage for the same human dramas.

A more recently emerging trajectory is to surrender the future to our machines. To build artificial successors and let biological life quietly lapse, severing a four-billion-year lineage and betraying everyone who carried it to us. Even the best versions of artificial intelligence we could devise seem unlikely to compare to the richness in sentience, meaning, and experience that biological evolution could give rise to when scaled to billions of planets for trillions of years. Our technologies should serve life and its vast future potential, not replace the thing that technology exists to protect.

Our greatest defense is humility. Surrendering control cuts against our instincts, but we should hold our role as a good parent does: to nurture, provide, and protect, while giving life the space to flourish on its own terms. We may need to serve that parenting role for millions of years, during which humanity can build its own future of abundance while tending faithfully to the life in our care.

A purpose on this scale is large enough to pull across generations, nations, and ideologies rather than split it along them. The first steps, mapping the galaxy, unlocking interstellar transport, engineering more versatile life, are within reach this century. It gives the march of progress, from our evolution through the agricultural, industrial, and digital revolutions, a direction far bigger than ourselves: a chance to rise from the ashes of our destructive past and become the constructive heroes on whom the future of life depends.

Now is the time to begin, but not to rush. As we grow rapidly in technological capability, we must see the summit we are aiming at so we do not climb the wrong mountain. And we must prepare carefully enough to climb the right one successfully, so the best future for life stays within reach. Such a purpose asks each generation to do what gardeners have always done: prepare the ground, and plant in faith for a harvest they will never see.

Every generation before us, every organism across four billion years and five mass extinctions, lived and died to place this choice in our hands. We are the one species able to end life’s only chapter or to begin its next. To take up that work is to honor the countless lives that carried the tree this far, and to serve the vast forest that will inherit the future we plant.

All that came before, and all that is yet to come, are watching us. Nothing has ever mattered more.

Donnacha Fitzgerald is a scientist and biotech founder working at the intersection of AI and bioengineering. He holds a PhD in computational biology from the European Molecular Biology Laboratory. His aim is to enable humanity to better navigate the design space of biology, our most important technology, to build a future of maximal flourishing for life on Earth and beyond.