Obituary: Ernst Mayr

Evolutionary biologist who saw himself as an `old-time fighter for Darwin'

ERNST MAYR was one of the world's leading evolutionary biologists. He was the last surviving architect of the unifying "evolutionary synthesis" developed in the 1930s and 1940s, which integrated Darwin's theory of evolution by natural selection with the principles of heredity embodied in the science of genetics. He took Darwin's work a vital stage further, by showing how species were actually formed: not by the infinitesimally slow drift of geological time as envisaged by Darwin, but comparatively quickly, and as a result not of change but of isolation.

Mayr saw himself as an "old-time fighter for Darwinism". "Please don't tell me what is wrong with Darwinism," he would say. "I don't see anything wrong with Darwinism." Looking back over a career spanning most of the 20th century, Mayr summed up its main phases:

Fifty or sixty years ago, I would have said without hesitation that I'm an ornithologist. Forty years ago, I would have said I'm an evolutionist. And a little later I would still say that, but I would also say I'm a historian of biology. And, for the last 20 years, I love to answer: I'm a philosopher of biology.

Ernst Walter Mayr was born in 1904 in Kempten, Bavaria, where his father, Otto Mayr, was a judge. On long Sunday-afternoon walks with his father, Ernst became passionately interested in birds and, by the age of 10, knew all of them by their calls. In line with other members of his family, he enrolled at a medical school, intending to become a doctor, but chose the University of Griefswald for its birdwatching attractions more than its medical reputation.

One birdwatching expedition led to a crucial meeting with Germany's foremost ornithologist, Erwin Stresemann. Ernst Mayr had spotted a pair of Red- crested Pochards, a bird that had not bred in Germany for 70 years. Pressing his claim led him to the Berlin Natural History Museum and Stresemann, recognising Mayr's talents, invited him to work at the museum during university holidays. In 1925, Mayr moved there full-time to study for a doctorate in zoology under Stresemann, which he completed in 16 months while simultaneously completing his pre-clinical studies at medical school.

In the tradition of Darwin and other Victorian naturalists, Mayr began his scientific career with an expedition to a remote part of the world. In 1927, he met the second Lord Rothschild at a zoological convention in Budapest. Rothschild was looking for someone to go to Papua New Guinea to collect the skins of birds of paradise for his private museum. On Stresemann's recommendation, he agreed to sponsor Mayr and, in April 1928, the latter began a year-long tour of the inaccessible mountains in the north of the island.

Over the next year and a half, Mayr shot around 3,000 birds of paradise and other exotic birds. The feathered skins were carefully preserved, while their bodies generally went into the pot for supper. According to Mayr, who claimed the world record for eating birds of paradise, they all tasted much the same. During that time he survived near-drowning in an upturned canoe, a hazardous descent of a waterfall, and attacks of malaria, dysentery and dengue fever. At one point he was reported to have been killed by tribesmen.

Among the brilliantly coloured skins Mayr sent to Rothschild were two species and 30 subspecies new to science. More important, however, was one of the classic "negative discoveries" of biology. Mayr had been unable to find several rare birds known only from skins. The reason, it later dawned on Stresemann, was that they were not species at all, but hybrids. It implanted in Mayr's mind the difficulties of reliably naming a species from skins alone without observing where it occurred and how it behaved in the wild.

Mayr subsequently joined the Whitney South Sea Expedition, where he participated in bird surveys of several islands, most notably in the Solomon Islands. This experience also set him thinking about the role geographical isolation might play in creating species.

In 1930, he returned to Berlin to find a telegram inviting him to come to the American Museum of Natural History in New York to work on the thousands of bird specimens collected by the expedition. He set sail the following year, and remained in the United States for the rest of his life. Later he became a US citizen, along with his wife Gretel, whom he married in 1935. Their marriage lasted until her death in 1990.

The piles of bird skins in Mayr's care increased substantially when Rothschild was obliged to sell his unrivalled collection of 280,000 skins to the American Museum of Natural History in the face of demands from a blackmailer with whom he had had an affair. Mayr's official work as curator of the collections informed his gathering insight into geographical variation and evolution. It enabled him, in 1942, to publish one of the landmark works of biology, Systematics and the Origin of Species.

In it, Mayr developed his conception of a species not as forms defined by their physical attributes but by their ability to interbreed. The American Blue Goose, for example, was of a different colour from the Snow Goose, and, on appearance alone, would be judged to be a different species. But they freely interbreed, and so, by Mayr's definition, are regarded as races of the same species. Mayr's definition of species as "groups of interbreeding natural populations that are reproductively isolated from other such groups" is now one of the cornerstones of biology.

Mayr's other great contribution to the "evolutionary synthesis" is the observation that evolution speeds up in isolated populations, such as islands. Under such conditions, small genetic mutations accumulate rapidly, leading to new populations better suited to their local environment. Eventually these become species, unable to mate and produce offspring with related species.

This theory of "allopatric speciation" was not new. But since, unlike the geneticists and mathematicians who then dominated evolutionary theory, Mayr's insights were firmly grounded in fieldwork and taxonomy, he was better able to provide the theory with working examples. Through the cogent arguments advanced in Systematics and the Origin of Species, Mayr's idea is now accepted by nearly all evolutionary biologists. Mayr's reputation rose accordingly. In 1947, he helped found the Society for the Study of Evolution, and for many years edited its journal, Evolution.

In 1953, Mayr left New York to become the Agassiz Professor of Zoology at the Harvard University Museum of Comparative Anatomy. He also served as curator of the museum from 1961 to 1970. On formal retirement in 1975, he was appointed Emeritus Professor and given an office at the university. Although in later years he spent the winter in the balmier climate of Rollins College in Florida, Mayr never retired. "My God, why should I?" he exclaimed on his 100th birthday. "I enjoy what I'm doing."

Mayr adapted well to the more informal manners of his adopted country, America. He was a feisty cheerleader for Darwinism, dynamic, provocative, opinionated and direct. He shared to the full Darwin's essential quality of persistence. He could have written Darwin's well-known dictum that doggedness is the secret of science. Long before the end of his life, Mayr was regarded as the master of evolutionary studies by the likes of Stephen Jay Gould and E.O. Wilson.

Mayr's prominence put him at odds with the growing number of creationists in America, but he refused to debate evolution with religious people, claiming that he did not wish to weaken their faith. However, his book What Evolution Is (2001) contained a section on arguments useful for encounters with creationists.

From the 1970s onwards, Mayr became more interested in the history and philosophy of science, culminating in his magisterial 974-page survey The Growth of Biological Thought (1982). An important strand of his writings was of the crucial role of the naturalist in the development of theory. Against the prevailing wind of modern times, Mayr was predisposed to see selection acting on whole animals and plants rather than on genes and molecules. "People without that naturalist experience don't have that feeling," he once said. "They don't know species." He was a holistic thinker in the Darwinist mould and central European philosophical tradition, inclined to dismiss the current preoccupation with individual genes as "beanbag genetics".

Mayr always retained his original love of birds, and teamed up with Jared Diamond to write The Birds of Northern Melanesia, published in 2001. By the end of his life, Mayr had written 25 books and over 600 scientific papers. His last book, What makes Biology Unique?, was published last year.

There is no Nobel Prize for Biology but, if there were, Ernst Mayr would have won it. He was the first scientist to win the "triple crown" of biology prizes: the International Balzan Foundation Prize in 1983, the Japan Society for the Promotion of Science's International Prize in 1994, and the Royal Swedish Academy's Crafoord Prize in 1999. He gave away most of the prize money to the Harvard Museum, the American Nature Conservancy and other charitable bodies. He also received the US National Medal of Science in 1970. In 2001, to honour the 75th anniversary of Mayr's receiving his first doctorate, the Humboldt University of Berlin awarded him a second and honorary PhD.

Ernst Walter Mayr, biologist: born Kempten, Germany 5 July 1904; Assistant Curator, University of Berlin 1926-32; Associate Curator, Whitney-Rothschild Collection, American Museum of Natural History 1932-44, Curator 1944-53; Professor of Zoology, Harvard University 1953-75 (Emeritus), Curator, Museum of Comparative Anatomy 1961-70; married 1935 Gretel Simon (died 1990; two daughters); died Bedford, Massachusetts 3 February 2005.