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Ernst Mayr, Biologist Extraordinaire

An appreciation of Harvard's visionary of modern evolutionary synthesis

Lynn Margulis

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.

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