David Layzer

David Layzer 1925-2019



Reflections - In Memoriam

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I never had the honor of meeting David Layzer in person. Nevertheless, I remain in his debt. His extraordinary and far-ranging intellect and his spirit of scientific integrity and academic honesty enhanced my career and changed my field, developmental science, for the better.

In the mid-1970s, I was working to complete what would be my first book, Concepts and theories of human development. I was struggling to address a reviewer’s comment about the then uncontested work of Sir Cyril Burt, a world-famous British psychologist who claimed that his research with identical (monozygotic) twins proved that intelligence, as measured by intelligence tests and indexed by IQ scores, was largely genetically determined.

Who was I, the reviewer asked, to question the validity of the research of Sir Cyril? Who was I to question the statistical usefulness of heritability analyses of genetic versus environmental sources of IQ scores? The reviewer suggested that I did not have the knowledge or stature to question Sir Cyril’s data analytic abilities.

Then I read an article published in 1974 in Science magazine by a professor of astrophysics at Harvard University, “Heritability analyses of IQ scores: Science or Numerology.” David Layzer had both the academic stature and the understanding of mathematics and statistics to challenge Sir Cyril’s use of them. I used his article to counter the reviewer’s questions and, I guess, to convince the editors to go ahead and publish my book. First published in 1976, the book has become one of the most used texts in graduate education in my field; the fourth edition was published in 2018.

David argued that heritability research in general (and, particularly in relation to IQ), involved advancing fallacious arguments and misapplying data. To begin with, Burt and others who relied on his data, declared that IQ is a trait, which in psychology is seen as an attribute that is innate and not susceptible to environmental influence. Therefore, because IQ was innate, then people with lower IQs were regarded as being of inferior “genetic stock.”

However, David pointed out that any alleged genetic difference, or “inferiority,” of people with lower-than-average IQ scores was based on assertions that made no scientific sense, that were significantly and egregiously flawed in several ways.

“Tests of IQ are precisely analogous to physical readings made with a black box —a device whose internal working is unknown. Because we do not know what an IQ test or a black box is supposed to measure or how it works, we cannot know to what extent measurements carried out on different subjects are comparable or to what extent they are influenced by extraneous factors. Thus, IQ scores contain uncontrollable, systematic errors of unknown magnitude. This helps to explain why different investigators frequently report such widely differing estimates of the same IQ correlation. Systematic discrepancies between measurements of the same quantity are never ignored in the physical and biological sciences, because they signal the presence of unsuspected systematic errors or of defects in the theory underlying the measurements.

IQ scores also differ from conventional measurements in that they have no strict quantitative meaning. The IQ is an index of rank order on a standard test, expressed according to a convenient but essentially arbitrary convention. In effect, the intervals of the IQ scale are chosen in such a way as to make the frequency distribution of test scores in a reference population approximately normal, but other methods of defining the scale could claim equal prior justification.

These considerations show that IQ scores are not phenotypic measurements in the usual sense”.

He concluded that:
“Under prevailing social conditions, no valid inferences can be drawn from IQ data concerning systematic genetic differences among races or socioeconomic groups. Research along present lines directed toward this end—whatever its ethical status—is scientifically worthless”

Later in the 1970s, it was demonstrated that Burt’s conclusions were not based on actual data. That is, the data were made up. No actual research was ever conducted. Nevertheless, even with much weaker data, genetic reductionists continued to claim that intelligence was largely inherited. And David continued to critique the claims of what he labeled as “IQ-ists.” Writing in 2000, he asked:

“How have biometricians who analyze IQ scores managed to occupy themselves for so many decades with strictly meaningless questions? The answer—or at least the most polite part of the answer—lies in their failure to formulate their mathematical model correctly” .
He concluded that:
“Biological, psychological, and sociological considerations make it seem highly implausible that IQ test scores could have the additive structure biometricians posit. For this reason alone, it seems to me that biometric studies of IQ are scientifically bankrupt”
Today, as we enter the third decade of the 21st century, David’s contributions, made over 40 years ago, continue to frame the correct understanding of the nature-nurture controversy in developmental science. And they continue to provide conceptual and methodological tools useful for combatting allegations that race differences are based on the presence of inferior genes.

His contributions to developmental science have done more than enrich all of the editions of my book. They modeled intellectual courage, in that he stepped beyond his own area of science to venture into another area and work to correct what he knew were fatal flaws in scholarship that, if uncorrected, could negatively affect human lives. His commitment to truth provided hope that the appropriate use of theory and statistical methodology could serve to correct fallacious arguments about alleged inevitable racial, ethic, and socioeconomic deficits in people. I am personally in debt to his scientific courage and acumen. And so too are millions of young people in our nation and world.


Scientists, even nice ones, can be kind of scary, but David was never like that. You felt you could say anything to him, no matter how stupid, and it would be OK. (Somehow, he managed to be this way without ever saying anything stupid himself.) That rare and liberating openness is the main thing about David that has stuck in my memory of him for over four decades now. For many young people that passed through his world, he offered a unique kind of unconditional acceptance, like a college-level Mr. Rogers: everyone is OK, everyone is special, and he really meant that, and it was really true. In a rigorous field that is intimidating even for insiders, David helped everyone participate, and share the depth and beauty of scientific ideas.

In cosmology, David sought to understand the origin of cosmic structure. He was one of a handful of individuals who had the wisdom, vision and courage to commit their work to a risky enterprise that at the beginning was not always regarded as a legitimate scientific inquiry, but has now, after half a century, brought us to a deep understanding of connectedness throughout space and time. Throughout his career, he realized that the quiet insight and confident, deeply-questioning independence of thought of a single individual can sometimes reach deeper into the nature of things than the accepted “wisdom” of a scientific community.

The main thing I want to say is Thank You, both to David and to Jean, for your kindness and generosity of spirit, for sharing the love and warmth of your home, for your shining examples of how to live and love and work and talk and listen, that helped to launch me into adulthood and indeed, showed me how to live.

Thanks again!

Craig Hogan



For David

His compass measures two points on the globe,
but time is running out in grains of sand.
His candle will not last the night: the last
page of the book of stars will be unread.
Galaxies whirl and rush apart. A low
noise can be heard throughout the universe.
Chaos evolves to sense by mathematics,
and Schrödinger's cat collapses into life.

Robert Layzer 8-20-19


Dear Jean,

Thank you very much for your note and news about David. You have my greatest condolence on your loss.

This news really hit me pretty hard. I can't totally get used to the fact that David isn't with us any more. I had sort of expected David to always be there and his absence makes a big hole in the world. He had a very large influence on my life - I once said to David that my father taught me how to speak and David taught me how to count. I remember that in giving a lecture to a class David would develop the mathematics on the blackboard from scratch, showing how each step was thought through and then executed, rather than copying the lecture onto the blackboard from notes written out beforehand as is usually done, and this method really informed my own approach to lecturing. Another most important thing I learned from David was how to get a ball-park estimate of a result from consideration of the most important physics coming into play - the "back-of-the-envelope" calculation - in order to get a feeling for a problem and decide whether a detailed calculation would be useful. This had an enormous influence on my way of thinking - part of how to count. Besides the astronomical explorations, those were very special days at Harvard College Observatory, including the squash and tennis games we had.

I'm extremely pleased to hear that David finished his book on Why We Are Free. Judging from the excerpts that he sent me I think this will be an important contribution not only to the question of free will but also be a unique overview of the different realms of physics. David had a very insightful take on the interplay of these different realms and it's important that it be entered into the library of human knowledge - I'm sure it will be on the top shelf.

Love, Tony


I came to know David at the end of his life. I’d known him for years, but the last months brought an intimacy that only a doctor can share with a patient as death comes.

It started with an act of courtesy, a kindness.   David was with a colleague, trying to sort out the vagaries of a pesky prostate. When leaning to pick up a scrap of neglected paper on the waiting room floor, he fell.

Falling can begin the begets of life, the dominoes that tumble on each other, a sequence of events that unravel precious life

David’s back was vulnerable. Aren’t they all?  

The years exact a toll with relentless minor strains, awkward twists, repeated lifts and bends.  

But more came to plague the life of this steady soul.   The bladder, the prostate, the nerves, the very tissues that connect and support conspired to create relentless pain.

David, dear David, patiently participated in all our efforts to find an answer, a cure, a mitigating treatment, a pathway to relief, even an explanation.

Drugs, tests, therapies one after another. But we lacked the power, the insight, the capacity to tame David’s pain.

But through this, David continued his work, his lifelong mission to explain the cosmos to any and all who cared to understand the boundless intrigue.

He would sleep in restless spurts, but the pain would always rip away him away from restoration. Then he would work, focusing, searching for the right words to explain the ideas that could not be suppressed.  

But the pain and the fatigue always returned, imposing, intruding, unrelenting. We worked in tandem, he with writing, me with doctoring

But David’s body was exhausted.   His long and vibrant life, so filled with music, was changed forever.   Life became survival.

David, the Harvard professor, the astrophysicist, the husband and father, the quartet master, the teacher, the mentor, the writer, the skeptic, the intellect, the synthesizer, was the David I knew. 

In those last weeks and days, at those final moments, I saw the deeper force that powerfully animated this man. 

At our last visit, David reclined at home in the sunlight of late afternoon.  I cheered him to rally. Gathering all his resources, he tried so hard to show me that he cared about my efforts on his behalf.

He was reassuring me, working to be a respectful and willing patient, not from some deep sense of deference but with trust and affection.  

He showed me that he cared about me, even as he knew, as only the dying know, that there was little left. In a twist of relations, I was in David’s care    

Here was the core of this man, his love for others, the engine of this long and productive life. Even as he faced death, he wanted me to know that he trusted me, trust being a gift of love. 

David understood the dispassion of nature, the inexplicable randomness of death.   He was too practical not to know that his physical self was spent.

But for David, living was the counterbalance to dispassionate nature.   Imagination, creativity, irreverence were his tools.

David was not one to pass on the opportunity to add the output of his brilliant mind to the world he inherited.  

So, as life ended, David left his creations for us all as gifts from a fellow traveler, a soul animated by love and affection.  

With these gifts, we survive.  

In memory of David Layzer
John Goodson, MD
March, 2020


Prof. Layzer was strongly supportive of women in astronomy. In the 1960s, several women at Harvard did research with him: Holly Thomis, Cara Joy Hughes, Claire Max, a former professor of Physics at Vassar (whose name I have forgotten), and me. If a student in Layzer's research group wrote a paper for publication, Prof. Layzer did not automatically add his own name as he wanted the student to get full credit. Here are some examples from my own experience.

First, a contrast. In my junior year, I took Astronomy 140 from Layzer, but I was assigned another male professor, whom I shall call "Nameless," as my astronomy dept. advisor. "Nameless" said to me at our first meeting, "It is a waste of time to educate you in astronomy since as a woman you will just get married and quit." To which I replied "What about Cecilia Payne Gaposchkin," and thought to myself "She has done more important work than you will ever do." For my senior year, Layzer was my official advisor. Before the fall semester started, I asked him which astronomy grad. schools I should apply to. He named the top six astronomy graduate departments in the U.S. Clearly Layzer did not have the same view of female students as "Nameless" did. Shortly thereafter, I learned my mother was terminally ill with cancer; she died that December. I decided that I needed to go a graduate school close enough to our home in Rhode Island so that I could go home weekends to be with family and help my 14-year old sister. Therefore I applied to only one graduate school: the Astronomy Dept. at Harvard. When I came back in January, I worried to Prof. Layzer about my applying to only one graduate school. He kindly said "You have been taking astronomy courses with our graduate students and doing as well as they do, so you shouldn't worry about getting into grad. school."

Layzer hired me as a research assistant for the summer before I entered grad. school. When I wrote up the results of the project, he told me to submit the manuscript to the ApJ with my name as sole author.

The Astronomy Dept. required graduate students to do two research projects, one observational and one theoretical. I began the latter in 1964 under Layzer's supervision; he suggested that I compute the radio and X-ray background to be expected from extragalactic sources. I decided to calculate the radio to microwave background that would be produced by a combination of emission from discrete extragalactic radio sources and intergalactic free-free emission. At that time, the existence of intergalactic ionized hydrogen was completely unknown.

After Penzias and Wilson measured the "excess antenna temperature" at 4.08 GHz, and before their result was widely known, Arno Penzias visited Harvard and talked to me. I noted that intergalactic free-free emission could account for the background they measured, and that their measured value provided an important constraint on the values of intergalactic electron temperature and density. Prof. Layzer told me to submit my result to Nature. He did not want to be listed as co-author because "people would know this was not his type of research." This Nature paper was widely cited but after the microwave background was measured at other frequencies, it became clear that intergalactic free-free emission was not the explanation for the CMBR.

When I completed my Ph.D. with Layzer on topics related to the Cold Universe, he helped me get a faculty position in the Physics Dept. at Brown, where he had a friend. I couldn't have asked for a more supportive advisor.


As a freshman in fall 1973, I pored over the Harvard course catalogue. There were so many enticing courses, so many new subjects to explore. But one course drew my eye above all others, a general education course named “Natural Sciences 90: Space, Time, and Motion.” The course promised a combination of astrophysics for nonscientists, philosophy, history of science, and more. I signed up and was enthralled from the first class meeting.

David Layzer was the genius behind that course. He, together with my experiences in the course, had a profound effect on my development as a student and future academic. I learned how to read scientific articles and reason through difficult ideas. I learned the excitement of taking ideas from one discipline and applying them to a different field. I polished my writing skills and delighted in small group discussions. The lessons of “Nat Sci 90” were like a rocket fuel that propelled me through the rest of my college years and into my career.

David himself was the essential ingredient of this propellant. His passion for learning, gentle stewardship of class discussions, and dedication to undergraduates were remarkable. At a time when most Harvard professors were faces on a large lecture stage, David nurtured undergraduates on their path to learning. I saw the impact of his efforts even more closely when I had the honor of serving as a teaching assistant in the course. David did not use his TAs to distance himself from undergraduates; instead, we supported the vibrancy and wisdom he shared with everyone.

I am grateful that so many classes of Harvard students had the chance to learn from David Layzer, and sad that no future freshmen will share that same delight. But David’s inspiration remains forever with all of us who knew him.

Deborah Jones Merritt, Harvard ‘77

As a lonely college student with a passion for string quartets, it was my good fortune to meet David and to be swept into the extended Layzer family, where along with so many others I have felt welcomed and included for nearly 5 decades. My visits to their home, which started in 1972, were usually for an evening of string quartets, a gathering that would begin with one of Jean’s fabulous meals and a far-ranging dinner conversation followed by David’s invitation into the music room, “We are not here for fun!” We visited and revisited the masterpieces of the chamber music repertoire and other pieces of less renown, sometimes with more zeal than success, always with camaradie and appreciation followed by dessert and more conversation. These evenings continued, gradually less frequently, until David’s declining health no longer permitted. I think everyone concerned remembers them with pleasure.

In the wake of David’s death, Jean allowed me to find homes for David’s collection of chamber music scores and parts. I had assumed my knowledge of his accumulated trove, neatly organized into folders and boxes, to be complete after so many visits to the music shelves in his living room, but as I shared the individual items with others of his musical circle, there were some discoveries and reminders of his remarkable character.

Alongside the standard repertoire, there were many obscure works, older and more modern, some in faded photocopies, all attesting to David’s breadth of curiosity and interest. His solo books, some of which must have been 70 or more years old, made clear his life-long devotion to mastering the violin through disciplined and continuous study. As a young man, clearly he must have worked through some of the most challenging classics from the concerto repertoire as well as the flashy showpieces of Wieniawski and Sarasate, carefully annotated with fingering and bowing markings. His Bach partitas were particularly marked and worn. A copy of the Ysaye solo sonatas and 4 editions of the Paganini caprices pointed toward a musical fearlessness that would have been in keeping with his willingness to tackle the most complex scientific, social and philosophical problems.

Like our bodies, printed music ages over the decades. The bindings loosen and break, the pages fade and lose their suppleness. They no longer bend or fold, they merely crack. Some of David’s music, like its owner, was laid to rest. David’s rapid aging, toward the end, was incredibly sad to watch, though he attempted to ease the pain of those who cared for him with his patience, grace, and gratitude for Jean’s unflagging ministrations. He had been a man of physical and intellectual strength and vigor and that is how I will remember him. It was a great privilege to know him and now to share loving memories with so many others in whose lives he played an unforgettable role.

Jim Ellison

David's Wikipedia page
David's German Wikipedia page (English translation).
David's Information Philosopher web page
David DeVorkin's 2007 oral interview for the American Institute of Physics
David's PhilPeople page
David's Books on Amazon
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1942, Senior Year

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One of Many Layzer String Quartets:
David, Sarah Co, Jim Ellison, and Dan Lee

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Four Generations:
daughter Emily Sherwood,
her daughter Pamela Sherwood Karlan,
and Pamela's daughter Helene