Ernst Mayr, Biologist Extraordinaire

An appreciation of Harvard's visionary of modern evolutionary synthesis

> <table cellspacing="0" cellpadding="1" width="100%" border="0"> <tbody> <tr> <td> <div class="assetContent"> <div> <p>Ernst Mayr, Harvard University professor emeritus and biologist extraordinaire, died peacefully in Bedford, Massachusetts, on February 3. He was 100 years old and had been associated with the biology department at Harvard since he joined its faculty in 1953. An era in evolutionary thought, called variously the New Synthesis, neo-Darwinism or the Modern Synthesis, came to an end with his passing.<p>

The death of the last of the great evolutionary biologists of the 20th century concluded an intellectual movement in the study of evolution—a point of view whose most striking aspect was the extent to which all of the evolutionary history of life on Earth was perceived as a subdiscipline of biology. Whereas Thomas Kuhn, author of The Structure of Scientific Revolutions, might have called it a paradigm, Ludwik Fleck (author of Genesis and Development of a Scientific Fact, 1935) would have recognized the correlated demise of neo-Darwinism and the death of Professor Mayr as a paradigm lost.

An accomplished naturalist, Ernst Mayr began his work in 1923 at the age of 19. The last of his 25 books, a collection of essays called What Makes Biology Unique? Considerations on the Autonomy of a Scientific Discipline, was published by Cambridge University Press in the summer of 2004, one month after his 100th birthday! This fact attests to Mayr's intellectual talents and unwavering interest in science, its history and philosophy.

And last May, shortly before Mayr's centenary birthday in July, an open celebration of his work and life was held in the auditorium of the Mineralogical and Geological Museum at Harvard. The place was crowded with admirers, spectators, students from universities and colleges from all over the Boston area and beyond. Several famous evolutionary biologists, colleagues, many of whom were among his former students and are now professional leaders, came to pay tribute. What struck me at this well-attended, enthusiastic gathering was that, among the marvelous lecturers in an all-day session about the evolutionary panorama of life on Earth, the most moving and informative of the talks, in my opinion, was the final statement by Ernst Mayr himself!

Mayr was born in Kempten, Germany (Bavaria), to an educated family, many of whom were physicians. His father, Otto Mayr, was a judge and a bird-watching enthusiast. During his school holidays Ernst worked at the Berlin Zoological Museum at the invitation of Erwin Stresemann, the best ornithologist in the country at that time. Following his two years of study at the University of Greifswald, oriented toward medicine as urged by his family, he completed his doctoral program in 16 months at the University of Berlin. Why did he opt to study at Greifswald? Why did he go north to a relatively unknown academic institution? Because his real interests were in the study of natural history, especially watching birds.

Nature Not Books

Like Darwin, Mayr was always fascinated by live animals in nature. He was particularly compelled by the question: How do species originate? Some three years before he died, he told me about his delight when the University of Berlin called him back to celebrate the 75th anniversary of receipt of his doctorate degree. I asked him if I might accompany him to attend the scientific program. "Oh, you don't want to do that," he remarked. "There will be no science, just endless and boring talks by administrators."

We had been discussing modes of speciation, and I had shown him our 10-minute film on Mixotricha paradoxa, an Australian termite protist, in his daughter Susanne Harrison's kitchen in Bedford. I had explained "symbiogenesis" as a mode of speciation. "I get it, I get it," he said, first pensively, then excitedly as he watched the five or more integrated microbial symbionts that comprise a single Mixotricha protist swim away as a single individual.

I tried to distinguish "symbiosis" from "symbiogenesis" for him. "Oh, you don't have to tell me what 'symbiosis' is!" he exclaimed, a little impatiently. "I studied symbiosis with Paul Buchner in Greifswald, who was a young instructor there" for a very short time before he moved on, eventually to Italy. Buchner, author of the seminal work Endosymbiose der Tiere mit pflanzlichen Mikroorganismen (1953), was the founder of modern symbiosis research.

Mayr took seriously Louis Agassiz's admonition. He studied "Nature not Books" between 1928 and 1930 when he collected more than 3,000 birds in the South Pacific, mainly the Solomon Islands and New Guinea. He learned to live off the land. After removal of the skin and feathers in the preparation of "study skins" and taxidermic samples for species identification, morphological analysis and shipment to museum collections, nothing would be wasted: The innards went to pot for dinner. That Ernst Mayr ate more birds of paradise than any other modern ornithologist is a well-known anecdote.

Mayr's work in the field, especially with avian diversity, led him to his most familiar contribution to science, documented in his two dozen single-authored or edited books and more than 600 scientific publications. He framed the animal species concept. Members of the same species can mate and breed to produce fertile offspring. Even plants and animals that greatly resemble each other are not to be assigned to the same species if they are not interfertile. On the other hand, animals that look very different from each other (such as Great Danes and Yorkshire terriers) if they produce fertile offspring do belong to the same species.

He told me about the wood duck and the green-headed mallards illustrated on his conservation-society shower curtain—that they were perfectly fertile, and a mating between these birds resulted in normal numbers of healthy chicks. He said that nevertheless he agreed that the two very different-looking ducks must be assigned, as they are, to two different species. Why? Because, he insisted, even when they live on the same pond, such as the duck pond here in Amherst, they only mate with their own kind. His definition of species, he insisted, is "organisms are members of the same species that, in nature, mate to produce fertile offspring."

He always emphasized the importance of the environment. Speciation could almost always be associated with geographical isolation. When members of the same species are separated for long times by environmental barriers (such as newly formed volcanic mountains, islands, rivers or climatic change), the barriers lead to impeded mating. It is these isolated populations that tend to form new species. The importance of geographical details in the origin and evolution of species was always emphasized. "I don't need to measure the pH and see that it is lower than six in that soil," he would say. "When sphagnum and cranberries grow in the bog there, we know what the pH must be." A proud naturalist, Mayr was a superb writer who communicated primarily by handwritten notes. He was the last of the neo-Darwinians to revere nature, work inside her and with her. His life always extended beyond the computer and mathematical models.

What Evolution Is

We celebrated the publication of our books, both brought out by Basic Books, in the summer of 2002. At his lovely retirement village, with the help of many friends as well as family (including Mayr's daughters Susanne and biologist Christa Menzel of Simsbury, Connecticut), we had a wonderful bibliophilic party. For our book (Lynn Margulis and Dorion Sagan, Acquiring Genomes: A Theory of the Origins of Species), Mayr had written the fascinating, not uncritical, foreword. But Mayr's book was what we all came to celebrate. For readers unfamiliar with his comprehensive opus spanning more than 75 years of scientific productivity on a panoply of evolutionary themes, I recommend that you begin with this one, his 24th: What Evolution Is. Designed for the curious, nonspecialist reader, it is a fine read for those interested in the achievements of importance in 20th-century evolutionary biology.

Not immodestly, Mayr considered his 2002 trade book to be the single best summary of uncontested, documented evolutionary thought. "Evolution" refers to the results of experimental, observational and theoretical science that support the common ancestry of all life on Earth. Yes, of course, people are primates directly related to other great apes such as gorillas, chimps and bonobos. Yes, of course, humans were not made by an all-seeing, all-knowing white-man deity. Indeed, evidence points to the possibility that several species of nonhumans became extinct because of our aggressive, even murderous, greedy ancestors. These early Homo sapiens, related to us, displayed traits that still abound!

The questions and answers, at the end of the book especially, help any reader, even one naive with respect to science, to understand the basic concepts of this most important area of study. Mayr's reasonableness is especially pertinent today in the face of ignorance, prejudice and religious fundamentalism. For those who try to deny the validity of science that uses carefully collected evidence from investigators worldwide, this book is a responsible antidote.

Some three weeks before his death, I called him at home in Bedford and asked, "Ernst, how are you? How do you feel?" He responded cheerily, "I feel fine. That is, I feel exceptionally well given the diagnosis." "What diagnosis?" I asked. "Didn't I tell you? The doctors tell me I have cancer. It has already metastasized, but I don't feel sick at all." "Oh, Ernst, I'm so sorry," I responded. "Well, Lynn," he said cheerfully, "I will have to die of something."

© Lynn Margulis