The other day I read a newspaper article about some new fossil findings relevant to human evolution. They involved some recently found fossil bones from Homo florensis, an extinct species, whose first traces were found 20 years ago, in 2005, on an island in Indonesia.
Species that belong to our genus Homo are termed “hominins”, which roughly means “human”. Each new fossil hominin discovered is of high interest but this was a sensation. It was a human species whose adults only reached about 3 ½ feet, far below the typical height of our species Homo sapiens. They also had much smaller brains than we do but made sophisticated stone tools. The popular press labeled them “hobbits”, in homage to the J.R.R. Tolkien creatures, and this nickname has stuck. Hobbit in size they may have been but being able to make good stone tools indicated high cognitive ability; it was this combination of traits that caught the scientific public’s imagination.
I will come back to this species and its significance in a few moments but here I remark that reading this article instantly reminded me of an older friend of mine who died that same year, at age 100. He was an eminent evolutionary biologist as I will discuss. His writings on human evolution argued against the possibility of a species like H. florensis. Clearly, he was wrong about this issue. 1
His name was Ernst Mayr and he was born in Bavaria in Germany in 1904. I suspect that his memory amongst biologists today is fading fast. For most biologists under 40, his name, if known at all, would be regarded as that of a figure from the deep past. Yet he deserves to be remembered. Not least, his story illustrates the fluidity and rapid flux of ideas in biological science.
He was a remarkable man, highly intelligent and very hard working. At age 21, he had earned both a medical degree and a Ph.D. (in ornithology). When, about 80 years later, I mentioned to him that this seemed a tremendous achievement to me, he pooh-poohed it, saying something to the effect that the requirements for advanced degrees were different and easier then. Perhaps but it is still impressive to me. After getting his degrees, he took a position to head up an expedition to study and collect Birds of Paradise in New Guinea. This too was fairly remarkable; he lacked prior experience in exploring jungles and to be given such a responsibility at such a young age was indeed unusual. The expedition was a great success.
In 1931, age 27, he became an assistant curator of birds at the American Museum of Natural History (AMNH) in New York City. He lived and worked in the United States for the rest of his life, though from 1953 onwards he was at Harvard University as a professor of biology, later an emeritus professor.
Birds remained a special passion of his throughout his long life but he earned his place in the history of biology through his work in evolutionary biology. That work was to help put the pieces together to create a coherent 20th century version of evolutionary theory.
All readers will know that, ultimately, we owe our basic ideas about evolution to that great 19th century scientist, Charles Darwin, beginning with the publication of his landmark book whose abbreviated title is The Origin of Species (or frequently just The Origin.) Darwin’s task, as he saw it, was two-fold but he only succeeded initially in one of the two goals. First, his book and its subsequent versions (there were a total of six), aimed to convince the world that evolution was a real process and that (probably) all living organisms on our planet were related through their history. In this, it was an undoubted success; thanks to Darwin, there was no going back to pre-evolutionary ideas after The Origin.
Darwin’s second aim was to establish that his greatest theoretical accomplishment, his theory of natural selection, was the essential explanation for how evolution occurred. Here, the picture was mixed. Indeed, it looked for about five decades to be a failure. There were many biologists who did not believe that natural selection had the power to explain all, or even most of, evolutionary change. The debates were heated and fueled by a combination of collective ignorance of much of the past history of life on Earth -- evolutionary history is notoriously hard to reconstruct – and large clashes of ego, sometimes titanic ones. By 1900, Darwin’s grand theory of evolutionary change – which he had hoped would assure his scientific immortality – was rejected by a major part of the scientific community. In one major later account of this history, it was said to have been “eclipsed”. Unusually for a scientific theory this failure was not by being replaced by a new one but by the massive doubts and discontents amongst biologists with Darwin’s idea.
Then, to change the metaphor from an astronomical image to a medical one, the theory began to revive from its comatose state. Its biggest deficiency, as Darwin knew full well, was in genetics. How could the hereditary systems that living organisms must possess have both the great stability they evidently possessed and the capacity to change gradually to allow the evolution or new forms, that is new species? Advances in genetics began in the early 1900s but the most important for evolution came between 1918 and the early 1930s. These made it possible to see how natural selection could power evolutionary change. If Darwin’s full theory had been the equivalent of being in a coma for decades, the patient was now at least, sitting up, able to eat and drink, and to receive visitors.
However, it was still bed-ridden, not yet ready to be discharged. There were still large areas of biology that had not yet been adequately integrated into an evolutionary framework. The principal ones were: paleontology (the study of extinct animals and plants), botany (the study of living plants) and systematics (the study of the degrees of relationship of different living things to one another). This is where Ernst Mayr came in, during the 1940s through the 1960s, and in a big way.
Though his specialty was birds and how the different bird species were related to one another, he was regarded by the early 1940s as an expert in systematics as a whole. In 1942, he was invited to give a prestigious lecture at Columbia University, one of the Jessup Lectures, on systematics. It was a big success he later told me, with a twinkle in his eye, because the previous speaker, one of the distinguished geneticists who had helped unify genetics and evolutionary ideas, had given his in a mumble. This lowered expectations for subsequent lectures, which Ernst well exceeded. However, better delivery was surely not the only reason for its impact. The published version shows how good it was in content; it included Ernst’s new definition of what a “species” was (see What is a “species”? An enduring question).
By this point, he was well connected in the world of biology. Seeing the problems in evolutionary biology, he started corresponding more and talking with people far beyond his immediate colleagues in systematics and fellow curators at the AMNH about evolution broadly. A major motivator of his at first was, I am sure, simply curiosity of the form “how can we explain phenomenon/fact X by the existing ideas” but, fairly soon, became a conscious project, whose aim was to create a contemporary theory of evolution based on, but far extending, Darwin’s ideas. By 1959, the centenary of the publication of The Origin, the unification project was not only complete but ready to be announced to the world. I was only a high school student of 14 at the time and remember some of this celebration without knowing the background history, the rocky road that Darwin’s idea had had to traverse over a century. Hence I had little sense of the significance of the achievement and knew nothing of Ernst Mayr then. 2. The new, updated theory was referred to as the Modern Synthesis or, later, the Evolutionary Synthesis. 3.
Of course, this work of synthesis continued apace over the following decades, as the revolution in molecular biology and other developments took place. Ernst contributed to these developments as well but, as is not uncommon in older scientists, his interests expanded and somewhat changed. They now more fully embraced the history of biology and the philosophy of science (and how the latter had to be different in some respects for biology than for physics). He produced two major books on these subjects in the early 1980s, shortly before his 80th birthday.
In the late 1990s, I heard him give a talk at a conference, when he was in his early 90s. I was struck by his clarity and his articulateness. It would have been a good talk delivered by someone decades younger but it was even more impressive because of his age. I am fairly sure that the germ of the idea of interviewing him for my journal formed then though it took several years for me to do anything about it. Finally, in 2002, I wrote to him, requesting an interview and we set it for early in May of that year. He had long been an emeritus professor at that point and did most of his work at home but once a week he went into Harvard, driving himself, where he would work for a day. However, we decided to do the interview at his apartment in his retirement home in Bedford, Massachusetts and that is what we did.
I tried to approach the task without preconceptions. His public image, based on his formal lectures, was that of a rather stern, dogmatic, indeed Teutonic presence and such a person would not be a lot of fun to interview. However, I suspected that that was not a fair or accurate picture – he had not seemed that way to me in the lecture I had attended – and put it aside. I was right to do so. From the first minutes of meeting him, it was clear that he was warm, friendly, had a good sense of humor and was a good listener.
We set up the tape recorder and began the interview, talking initially for two hours before we broke for lunch and resumed for a further two hours afterwards. I had not sent him the list of questions beforehand and so it was a spontaneous conversation. He spoke clearly in sentences and paragraphs, without pauses or filler sounds (like “um”). When I edited the transcript later, almost all my editing was in rearranging sections, not changing any of his wording or fixing anything. Of course, he had talked and thought before about all of the topics we dealt with but, still, it was impressive.
I have briefly talked about “super-agers”, elderly people who have the mental agility, memory and clarity of people decades younger (see Why do we age? Part 3) and I am certain that Ernst Mayr was a super-ager. He was 98 at the time of our interview but mentally in excellent shape. He did mention, however, that perhaps his memory was not as good as it had been. The example he gave, which he said had him thinking about this, had been a recent conversation in which he could not recall the name of a certain drink. Finally, it occurred to him: Campari. He laughed about it but I felt that it did worry him a bit. My unspoken reaction was along the lines of “If I live to 98 and something like that should be my worst memory lapse, I will be lucky indeed. “ (At 80 now, my memory is not bad but already slightly worse than his at 98.)
We talked about 4 hours altogether and later my secretary typed up the transcript. 4 While the interview was being made ready for publication, Ernst and I exchanged a few notes by email but we enjoyed each other’s communications and soon actually started writing letters, which we continued to do for a further 2 ½ years. Thus, as I approached 60, I found myself becoming a regular correspondent with one of the great biologists of the 20th century. It was an epistolary friendship, very 19th century in retrospect. Unexpected? Of course. Wonderful? Definitely.
The letters were not deep discussions of evolutionary matters but more chatty exchanges about what we were doing, people in the field, reminiscences, our respective pasts. (At one point, for instance, Ernst told me something about his mother’s life.) A few years ago, I donated the letters to what is now the Ernst Mayr Library at Harvard, and that is now their home.
One last thing about him and this brings us back to Homo florensis, the hobbit hominin. One of Ernst’s great qualities was his being unafraid to admit that he had been wrong occasionally about various things. (Some of these errors we discussed in the interview.) Of course, in his final decades, he would have been sufficiently secure to know that he could admit to having made mistakes without doing any harm to his reputation. Yet, my feeling is that he always had the intellectual integrity to do so. If new facts come to light, which bring your previous interpretation into doubt, you change your mind, admit your mistake and move on. Not everyone, especially some eminent scientists, can do this.
His error in the 1950s and ‘60s about human evolution, a viewpoint he held for some time, was that it was essentially a line, with one major new hominin species replacing the previous one. This was consistent with and indeed based on the existing fossil evidence until sometime in the 1970s. The line could have been represented something like this:
Homo habilus → H. erectus → H. neanderthalis → H. sapiens
At that time, this was reasonable. However, as new fossils of hitherto unknown hominin species were discovered and dated, it became clear that at many points in human evolutionary history, there must have been multiple co-existing hominin species. Since the branching had begun early, the hominin family tree was certainly not a line but also not so much a tree structure as a bush. H. florensis was one of the branches, from about 700,000 years ago to maybe 100,000 years ago. In contrast, H. sapiens is a younger twig, “only” about 300,000 years old.
A question to end on: how should one view Ernst’s life in retrospect? Very many of his detailed ideas about evolution have had to be modified or abandoned – I suspect that, in contrast, much of his detailed ornithological work remains intact – and there are big debates about the state of the Modern Synthesis today (see What is odd about the “theory of evolution”?), hence his biggest achievement looks less solid than it did 70 years ago. Does any of this diminish his legacy? To me, not at all. He had a wonderful life. That is not just an inference, he told me so directly. And he contributed greatly to the biological science of his time. In doing so, a lot of those ideas became the foundation for what came later even if the latter looks very different. My guess is that if he could come back and look at evolutionary biology today, he would be thrilled by its richness, and would not mourn those of his ideas that have not survived.
This article is Zimmer, C. (2025). An even smaller twig on the human family tree. The New York Times (Int’l Edition), 9-10 August, 2025, p. 2
Ernst’s contribution might seem relatively modest, namely talking to and corresponding with people and helping them synthesize their views. It seems much less dramatic than having brilliant insights into particular problems. Yet, it is a real gift and few people do it really well. Someone else in this category was J. Robert Oppenheimer, the father of the atomic bomb. Many of his colleagues at the Manhatttan Project thought he was the most brilliant of all of them yet he produced no individual ground-breaking insights in physics nor win a Nobel Prize. However, bringing ideas together was a special ability of his. Interestingly, he performed this work in the early 1940s as Ernst Mayr was beginning his evolutionary synthesis work. Perhaps this was a good period for people of this ability and temperament.
There is no single author good book on the Modern Synthesis after it was complete. (There was an earlier one, written by Julian Huxley, from 1942, well before the synthesis was complete and its title was the source of the term.) There is, however, an excellent multi-author history. It is Mayr, E. and W.B. Provine, eds. (1980). The Evolutionary Synthesis: perspectives on the unification of biology. Harvard University Press: Cambridge. A much shorter and later history, with a particular focus on Ernst Mayr’s role, is Wilkins, A.S. (2008). NeoDarwinism. In Icons of Evolution: An encyclopedia of people, evidence, and controversies, vol. 2, pp. 491-516. ed. B. Regal. Greenwood Press: Westport.
Interview with Ernst Mayr (2002). BioEssays 24: 960-973.