Charles F. Stevens (1934-2022)

There is a PDF of this with figures. It is my closing talk for the memorial symposium held at the Salk on May 4-5, 2023.

Hello all. I am William Calvin. I was Chuck’s first graduate student. I am having a rough voice today, so I will have a robot voice read this—35 years after Terry’s text-to-speech efforts. Do forgive the way the Polish surname of Mark Kac is pronounced.

I arrived in Seattle in the summer of 1962, as a graduate student at the University of Washington’s Department of Physiology & Biophysics. Chuck arrived in the summer of 1963, a year before finishing his Ph.D. in 1964 at the Rockefeller.

Chuck soon recruited me to work with him on the stochastic processes underlying synaptic noise and their effects on the interspike interval variability of cat spinal motoneuron’s rhythmic firing.

Chuck and I had many long conversations in his office, almost every day. So did Katherine Graubard after 1964; she too became an early Ph.D. student of Chuck’s. He had started working on invertebrate neurons, prospecting with day trips up to the University of Washington’s marine lab in the San Juan Islands near Victoria.

Each time, he chartered a float plane to go from the dock near the med school and fly 70 miles to the Friday Harbor Lab’s floating dock. Chuck invited Katherine to tag along when there was an extra seat on the plane. Soon she went up for a summer to take the marine invertebrates course.

She eventually did the neurophysiology part of her Ph.D. thesis up there. The second part involved electron microscopy, and the third part was modeling those Aplysia neurons whose capacitance was greatly augmented by all of the membrane infoldings.    

Dan Gardner showed you his good picture of Chuck from the 1970s. It’s a much better portrait than I was going to show you. Note the dial telephone on his desk.

I think that the best thing for me to emphasize, for this audience, is how and where Chuck’s scientific mind matured. He didn’t talk much about it, so this is mostly an inference from conversations between 1963 and 1974, aided by his C.V.    

Chuck must have started at Harvard in 1952, just as President Truman was finishing his second term and Ike was being elected.

Chuck’s Harvard major was Experimental Psychology. One must recall that this was the era of B. F. Skinner at Harvard, and so Chuck operated on white rats in the mid-1950s —something about lesioning hypothalamus, I seem to recall.  

Then from 1956 to 1960, Chuck was off to Yale for his MD.  He spent the summer of 1959 recording from squid axon at MBL. He was looking at the variability of the spike threshold, no less.

I never heard Chuck relate any stories from either Harvard or Yale. Nothing about Skinner or other famous professors, nothing about Woods Hole.

Why did he go to med school? I never learned. But somewhere during the 1950s, a passion for harder science came to dominate, overlying any Skinnerian-era psychology.

I seldom saw traces of Chuck’s medical-school education—say, in conversation, Chuck suggesting a differential diagnosis to be considered. By 1963, his persona was already that of a creative, enthusiastic yet carefully spoken, basic scientist. He seemed equally at ease with physics, math, and biology. That probably came from his time at the Rockefeller.

 1960 was the year that JFK was elected President and Chuck went to “The” Rockefeller for his Ph.D.     

Chuck worked with Keffer Hartline on self-inhibition in the Limulus eye. His thesis title was ‘A quantitative theory of neural interactions: theoretical and experimental investigations.’ It laid out a mathematical theory of computation in the nervous system. Hartline, in his 1967 Nobel Prize lecture, explained:

[quote] Before we can understand fully the dynamics of inhibitory interaction, we must consider a new feature of the inhibitory process in the Limulus eye: the inhibition of a receptor unit by its own discharge. This was first analyzed by Stevens and has recently been studied by Purple and Dodge. They present evidence that this "self-inhibition" may be a synaptic process like lateral inhibition ….

The intellectual history that Chuck did frequently mention to me usually concerned the probability theory and relevant physics that he had learned from Mark Kac at the Rockefeller.    

Chuck’s 1966 book, Neurophysiology, A Primer, seemed straight out of the Kac and Hartline years at the Rockefeller; Chuck had not been teaching the subject in such depth except via one-on-one’s at the large blackboard in his office. Katherine Graubard and I were among the early beneficiaries.

Keffer Hartline, you likely know already as a pioneer in single-neuron recording, using it to analyze lateral inhibition circuitry in horseshoe crabs. I read his papers as an undergraduate; lateral inhibition was the core of my undergraduate honors thesis in physics in 1960. But if I am to convey what helped to form Chuck’s approach to science, I also need to acquaint you with Mark Kac.    

A widely quoted quip of Kac's was his distinction between “an ordinary genius like Hans Bethe and a magician like Richard Feynman.”

All three were on the Cornell faculty in the late 1950s. In 1961, Kac left for The Rockefeller Institute in New York City.

Kac wrote an autobiography, Enigmas of Chance, published posthumously in 1987. When Katherine Graubard and I were at Woods Hole that summer, the new book exhibit in MBL’s main lobby had Kac’s book. I took it back to Seattle and read it.

In its preface, Gian-Carlo Rota said:

Mark Kac was one of the founders of probability theory. But more than a theory, probability was, to him, a new way to the truth of science…. he inspired the first generation of scientists who learned to think probabilistically….

That’s starting to sound like the Chuck Stevens we knew.  

It took me until the 1980s to master the mindshift needed to think probabilistically about Darwin’s evolutionary process, about allopatric and sympatric speciation as population sizes boomed and crashed, about genes going to fixation.

I didn’t realize that Chuck had also begun thinking about evolving the neocortical wiring patterns. Then in 1988, we ran into one another in some hallway somewhere.

Chuck asked me how I was coming with my review of Gerry Edelman's book, Neural Darwinism, that Science had asked me to write. Chuck advised me not to hesitate to straighten out Gerry on evolutionary process as applied to neocortex.

 I doubt that my book review changed Gerry’s thinking about what was truly Darwinian. But for me, my invited piece for Nature, “The brain as a Darwin Machine” in 1987, and then Chuck’s set-him-straight challenge—together they started up a dozen years of thinking about the layer-two neocortical circuitry which offered the possibility of making copies of spatiotemporal firing patterns, thanks to exciting triangular mosaics about a half millimeter wide. It could, I thought, serve to define a Hebbian cell assembly that cloned itself.  

While I began with the connectionist darwinism that Gerry and Chuck were imagining, I soon switched from an anatomical to a physiological darwinism. I began using my evolutionary biology to ask what it would take for a cortical circuit to be suitable for running a true Darwinian process—say, on the time scale of shaping up a novel sentence to speak.

 The immune response had already provided a darwinian example of how to improve quality within weeks with differential reproduction of the more successful antibodies. How about a Darwin Machine in a patch of cortex capable of producing high-quality physiological function—and on the timescale of thought and action? One-off plans for novel actions, not just selecting a learned action to repeat.

That turned into my 1996 monograph, The Cerebral Code, from MIT Press. I tried to make Darwin’s process more abstract, stripping it of biological specifics such as DNA and recombination and haplotypes. I identified six essentials for a Darwinian process:

"a pattern that copies with occasional variation, where populations of the variants compete for a limited workspace, biased by a multifaceted environment, and [where most of] the next round of variations [come] from the more successful of the current generation [heredity]."

All six are essential if the recursion is to keep improving quality. You cannot, as many do, leave out copying or heredity. Otherwise your process will dead-end. What people were calling Darwinian was usually just competition for a limited workspace, with synaptic pruning biased by a multifaceted environment.    

It is often remarked that Chuck, while running an experimental research lab, was really a theoretical scientist at heart. That was certainly my impression even in the 1960s. Yet in the early 1970s, when noise theory alerted him to how marginal even field-effect transistors would be for recording ion channels opening and closing, he dug into designing electronics circuits for recording such buried-in-the-noise events.    

His occasional postdoc at the University of Washington, Erwin Neher, went with Chuck to Yale med school in 1975. Erwin further developed Chuck’s techniques and went on to co-create [with Bert Sakmann] the patch clamp method which after 1982 created a revolution in many branches of electrophysiology.

Chuck’s 1996 book on theoretical physics did not come as a surprise to us, as his sabbatical leaves always seemed to feature math and physics. He consistently wandered off the neuroscience reservation. 

Katherine recalls Chuck wondering aloud once about whether, “Were I stranded on a desert island without a library, could I reproduce modern physics?”    

I like to imagine Chuck would have done this with a long stick, sketching curves and writing equations in the sand. That is, of course, much like he gave his lectures with no slides. Chuck’s deadpan humor would have led to saying how convenient it was to have his “blackboard” wiped clean by the next high tide.

I, too, have had such a wandering-off-the-reservation experience. I will omit the paleo-climate and paleo-anthropology steppingstones, but where I ended up—well, it has proved to be in a territory from which I cannot return, except for brief interludes such as this one.    

My 2019 book cover shows that I have been captured by the climate problem. I have been camping out with the climate scientists part-time since 1980, initially because our ancestor’s brain size tripled during the back and forth of the ice ages. One organ tripling in 2.5 million years without enlarging the rest of the body is very fast in the annals of evolutionary biology.

Evolutionary speed-ups usually happen when climate change keeps repeating. I wanted to know what there was in our ancestors’ environment and ecology that could promote brain enlargement.

Gradually I learned a lot of atmospheric science and oceanography. Like Chuck with the physics core, I kept asking myself if I understood their subject well enough intellectually so that I could explain it to a more general audience, sketching in the sand if necessary.    

I got the chance in 1997 when the editor of The Atlantic phoned me repeatedly, trying to persuade me to undertake the history of Gulf Stream failures.

  But in the aftermath of my 1998 cover story, I discovered that climate scientists simply did not think like those of us teaching in medical schools, especially where watching the clock and collapse were concerned. They were thinking like most basic scientists.    

 There is a gap in the basic science mindset, rather like the one in probabilistic thinking that Mark Kac addressed. I started out with it myself, but during my 20 years on the neurosurgery faculty, I  absorbed the medical mindset for heading off collapse. That is what I am trying to put on the climate agenda.

 So here I am at age 84, writing about how to stay away from slippery slopes and then back out of the danger zone for more climate flips. I emphasize its urgency, given the lead time needed for big projects to have an effect.  

Between 2002 and 2010, five sudden surges in extreme weather occurred. It was surge-and-stay. For example, in 2008 the number of billion-dollar windstorms jumped to six times the 1980-2007 baseline. Now they are occurring at nine or ten times baseline.

This is no longer gradual change. Climate has become unstable. Neurophysiologists—certainly Chuck’s people—are familiar with gradual change becoming unstable and going “pop”, but the rest of the world doesn’t think that way—except, perhaps, those who have had the experience of falling off an unstable ladder.  

In closing. Last October, Chuck demonstrated another model we might all hope to emulate someday (but not soon). Chuck died both unexpectedly and in the middle of the night. That’s far better than the alternatives.

You have no idea what a treat it is to be hanging out with so many others who have absorbed some of Chuck’s way of thinking. May we all prosper, despite no longer being able to try out our ideas on Chuck. Enjoy the sunshine.