Earlier today, my best friend Frank Padilla had driven Merry and me out to Font's Point.

We are midway through two weeks exploring Anza-Borrego Desert State Park, and Frank — who knows this desert the way I know the San Jacinto Mountains — wanted us to see the overlook into the Borrego Badlands. The road in follows Font's Point Wash, four miles of soft sand requiring four-wheel drive, the kind of access that filters out the casual and rewards the committed. When we reached the rim and stepped out, I understood why Father Pedro Font, chaplain and diarist on Juan Bautista de Anza's 1775-76 expedition to Monterey, described this vantage point as the "sweepings of the earth."

He meant desolation. I saw four million years of story.

The Borrego Badlands spread below us in corrugated ridgelines of conglomerate, sandstone, claystone, and mudstone — Pliocene and Pleistocene sediments laid down when this basin received the ancestral Colorado River as it carved the Grand Canyon, and before that, when delta-marine waters of the northern Gulf of California covered the land. To the east, the Salton Sea shimmered in the haze. The Santa Rosa Mountains rose to the north. We were standing on one of the finest exposures of deep geological time in North America, a place where the earth's layered memory is carved open by wind and water for anyone willing to make the drive. Above us, Swainson's Hawks circled on the thermals rising off the badlands.

We returned to Borrego Springs by noon, ahead of temperatures that would crest above ninety degrees. Over lunch, Merry looked up from her laptop and told me Paul Ehrlich had died on March 13th in Palo Alto. He was ninety-three. Cancer, in the end, though the obituaries were already framing the story around older battles — The Population Bomb, the Simon bet, the predictions that didn't come true on schedule. The critics were sharpening their knives before the body was cold.

I sat with it for a while. Anza-Borrego Desert State Park is one of the largest protected areas in the world — over 600,000 acres of bajadas, palm oases, slot canyons, and creosote flats, a vast expanse of public land set aside because people decided it mattered. Merry and I were spending two weeks exploring it, with some of my time devoted to work at the Steele/Burnand Anza-Borrego Desert Research Center — using an Insta360 X5 camera to create 3D Gaussian Splatting photogrammetric surveys, building baseline ecological documentation of a landscape under accelerating stress from a changing climate. A March heat dome was settling over the Southwest, pushing temperatures into territory that desert ecologists are learning to dread.

I had just spent the day staring into four million years of deep time, and now I was mourning a man who spent his life warning about the thin, precarious present. Here I was, a seventy-one-year-old field ecologist, still throwing pebbles on the track.

That phrase — pebbles on the track — comes from Michael Soulé, and it has stayed with me for forty-six years.

The Cornell Workshop, 1980

In the fall of 1980, I was a second-year doctoral student at Cornell, twenty-five years old and running on the kind of energy that comes from discovering your life's work. I had arrived in Ithaca the previous year carrying an unusual preparation: a bachelor's and master's in biology and ecology from Cal Poly Pomona, four summers as a wilderness park aide in Mount San Jacinto Wilderness State Park, and two years of environmental consulting that had taken me from Admiralty Island in Alaska to the San Juan River in New Mexico. I knew how to do fieldwork. What I was learning at Cornell was how to think about it.

Ted Hullar, the Director of Research for the College of Agriculture and Life Sciences, had taken me under his wing. Ted was a chemist by training — co-discoverer of the Hanessian-Hullar reaction — but he had a political mind and a passion for wilderness conservation that made him the perfect champion for a young ecologist with entrepreneurial instincts. When I proposed organizing a workshop to help define the emerging field of conservation biology, Ted found the funding without hesitation. This was years before the discipline had a professional society or even a settled name. Ted backed things before they had pedigrees.

The speakers we assembled read, in retrospect, like a founding document. Michael Soulé was there — he had organized the first major conservation biology conference at UC San Diego just two years earlier, and would go on to convene the 1985 Ann Arbor meeting that formally launched the Society for Conservation Biology. Peter Brussard came, a population geneticist working on butterfly demographics who would later chair the board of that society. Reed Noss was there too, very early career, a young ecologist who would become one of the architects of systematic conservation planning and the wildlands network concept. We invited Paul Ehrlich. He had prior commitments and couldn't attend.

His absence was a presence. Every conversation in that room was shaped by the intellectual framework he and Anne had built. I had been reading the Ehrlichs since my undergraduate years at Cal Poly, starting around 1972 when The Population Bomb was the book you couldn't avoid if you cared about the living world. Their work was the water we swam in — the I = PAT equation with John Holdren, the coevolution paradigm with Peter Raven, the insistence that ecology had policy consequences and that scientists had a responsibility to say so publicly.

But it was Soulé's keynote that branded itself into my memory.

Mike Soulé was a Zen Buddhist, and he delivered his assessment of the biodiversity crisis with the calm detachment of someone who had sat with hard truths until they stopped triggering the usual emotional responses. He offered a metaphor. Imagine, he said, that the world's biodiversity is on a train, hurtling toward a chasm. The bridge ahead is broken. The train lacks the brakes to stop in time. And we — the people in this room, the scientists trying to build a new discipline to address this crisis — can merely throw pebbles on the track.

Not because the pebbles will stop the train. But because throwing them is what we can do.

There was no anger in it, no rallying cry, no call to the barricades. Just a clear-eyed assessment delivered with the equanimity of someone who understood that the scale of the problem did not excuse you from the work. The room was quiet afterward. I was twenty-five years old, and I had just heard the operating principle that would govern the next four and a half decades of my life.

The Ehrlichs' Arc

The year after our workshop, Paul and Anne published Extinction: The Causes and Consequences of the Disappearance of Species. They came through Cornell on the book tour, and I bought a copy and had it signed. I still have it. That book, more than The Population Bomb, spoke directly to what we had been trying to articulate in our workshop — the systematic unraveling of biological diversity as a consequence of human activity, framed not as sentiment but as science.

The Ehrlichs' intellectual range was staggering. Paul had trained as an entomologist specializing in Lepidoptera — butterflies — and his early scientific contributions were models of careful empirical work. The 1964 paper with Peter Raven on coevolution in butterflies and plants essentially created a subfield. He understood population dynamics from the ground up, from years of tracking checkerspot butterflies at Jasper Ridge. When he and Anne sounded alarms about extinction and population, they were extrapolating from data, not from ideology.

This is what the obituary writers who focus on failed predictions consistently miss. Ehrlich was not a prophet. He was a population biologist who understood exponential curves and nonlinear systems and who chose, at considerable professional risk, to communicate what he saw to the public. His timeline for famine was wrong. His understanding of the underlying dynamics — that a growing human population pressing against finite resources and ecosystem services would generate cascading crises — was not.

As my career advanced, I encountered the Ehrlichs in a different context. Through my involvement with the Organization of Biological Field Stations, I attended annual meetings frequently held at the Rocky Mountain Biological Laboratory in Gothic, Colorado. RMBL was one of the great biological field stations in the world, and the Ehrlichs had conducted research there for years. They invested in a faculty cabin. At RMBL you didn't encounter Paul Ehrlich the television personality or the Population Bomb polemicist. You encountered Paul and Anne the working field scientists, still engaged with butterflies and population dynamics, still doing the patient empirical work that underwrote everything else.

Those RMBL encounters mattered to me because they confirmed something I had intuited at Cornell: the people building conservation biology were not armchair theorists. They were people who got muddy, who spent long days in the field, who understood that ecological knowledge comes from sustained engagement with actual landscapes and actual organisms. Soulé worked with grizzlies and mountain lions. Brussard tracked butterfly populations. Noss walked transects through longleaf pine forests. And Ehrlich, for all his fame, kept going back to Gothic to count checkerspots.

The Royal Society Paper

In 2013, the Royal Society invited Paul to write a Perspective paper marking his election to their fellowship. What he and Anne produced — "Can a collapse of global civilization be avoided?" — is, I believe, the most important synthesis of their life's work.

The paper is devastating in its clarity. Drawing on seventy-eight citations, the Ehrlichs systematically catalog the interlocking crises — climate disruption, accelerating extinction, land degradation, ocean acidification, groundwater depletion, global toxification — and demonstrate that these are not separate problems but interacting components of two gigantic complex adaptive systems: the biosphere and the human socio-economic order. They introduce the concept of "endarkenment" — a growing movement toward religious orthodoxies and ideological rigidity that rejects empirical evidence, democratic governance, and the separation of church and state. Climate denial, they argue, is not merely a policy failure but a symptom of civilizational regression.

Their conclusion is characteristically honest. Can collapse be avoided? Technically yes, because the knowledge and tools exist. Practically, the odds are small, because the classic signs of impending collapse — diminishing returns to complexity, institutional paralysis, cultural resistance to necessary change — are everywhere. But their ethical values, they write, compel them to struggle anyway, to increase even slightly the chances of a better outcome for future generations.

Reading that paper now, in the Anza-Borrego desert in March 2026, I hear Soulé's metaphor translated into the language of systems science. The train is still moving. The bridge is still broken. And the Ehrlichs, like the rest of us, kept throwing pebbles until the very end.

Still on the Track

Paul Ehrlich died three days ago. Michael Soulé died in 2020. Peter Brussard died in 2017. Ted Hullar, who funded that 1980 workshop without knowing he was investing in the birth of a discipline, died last September. The generation that built conservation biology is leaving us, one by one, and the critics who outlive them will continue to score points against predictions made half a century ago while the underlying crises those predictions addressed accelerate beyond anything the Ehrlichs imagined.

I think about what has changed since I sat in that Cornell room in 1980 and what hasn't. The human population has more than doubled, from 4.4 billion to over 8 billion. The proportion of the world's wildlife populations has declined by roughly seventy percent. Atmospheric CO₂ has risen from 338 parts per million to over 425. The discipline we were trying to define that fall has matured into a global enterprise with journals, societies, graduate programs, and an enormous body of knowledge — and the trends it was created to address have continued largely unabated.

And yet here I am in the desert, still working. Using tools that didn't exist even five years ago — 3D Gaussian Splatting, AI-assisted ecological analysis, distributed sensor networks — to document a landscape that Paul and Anne would have recognized as exactly the kind of place that matters. Anza-Borrego is a baseline, a reference point, a place where you can still see what the Colorado Desert looks like when it's mostly left alone. That baseline is shifting under the pressure of a changing climate, and documenting that shift is the kind of work the Ehrlichs spent their lives arguing we should be doing.

This is what I want to say about Paul Ehrlich, on the morning after his death, from a rental in Borrego Springs where the ocotillos are blooming out of season because the heat dome arrived early this year: he was right about the things that matter. Not about every timeline, not about every specific prediction, but about the fundamental relationship between a growing human enterprise and a finite biosphere. He was right that scientists have a responsibility to speak publicly about what they know. He was right that the erosion of empirical reasoning — his "endarkenment" — poses a threat as grave as any ecological crisis. And he was right that the work must continue regardless of the odds.

Soulé's train is still moving. The bridge is still broken. Some of us, the ones who were in that room in 1980 and the generations who followed, are still out here throwing pebbles. Paul and Anne Ehrlich threw more pebbles, and larger ones, than almost anyone else in the history of the discipline they helped create.

The desert is quiet this morning. A Costa's hummingbird is working the chuparosa outside our rental in Borrego Springs, its violet gorget catching the early light. A roadrunner pauses on the low wall, fixes me with its yellow eye, and vanishes into the creosote. These are organisms whose populations Paul would have understood in terms of dynamics and trajectories, not just as scenery. That's the gift of a life spent paying attention: you learn to see what's actually there, and what's disappearing, and you don't look away.

Rest easy, Paul. The pebbles continue.