Ernst Mayr was one of the 20th century's leading evolutionary biologists. He was at the same time a naturalist, an explorer, an ornithologist and science historian. His work contributed to the conceptual revolution that led to the modern evolutionary synthesis of Mendelian genetics and Darwinian evolution, and to the development of the biological species concept.

Neither Darwin nor anyone else in his time knew the answer to the 'species problem': how could different species evolve from one common ancestor. Ernst Mayr approached the problem with a new definition for the concept 'species'. In his book 'Systematics and the Origin of Species' (1942) he wrote that a species is not a group of morphologically similar individuals, but a group that can breed only among themselves, excluding all others. When groups of identical individuals get isolated, the sub-populations will start to differ by genetic drift and natural selection over a period of time, and thereby evolve into new species.

His theory of peripatric speciation (a more precise term for the subset of allopatric speciation he supported) based on his work on birds is considered as one typical mode of speciation, and is the basis of the theory of punctuated equilibrium. Apart from biological subjects, his prolific writings include works on the philosophy and history of science in general, and of biology in particular.

Biography
Mayr was born in Kempten and completed his high school education in Dresden. He planned to become a physician and completed his preclinical studies in 1925. However he was attracted to ornithology, and was introduced to Erwin Stresemann due to his claimed sighting of Red-crested Pochards in Germany, a species that had not been seen in Europe for 77 years. After a tough interrogation, Stresemann accepted and published the sighting as authentic. Stresemann offered him a position with the Berlin Museum and the prospect of bird-collecting trips to the tropics on the condition that he completed his PhD studies in 16 months. Mayr completed his PhD in ornithology at the University of Berlin in June 1926 at the age of 21 and accepted the position offered to him at the Museum.

At the International Zoological Congress at Budapest in 1927, Mayr was introduced by Stresemann to banker and naturalist Walter Rothschild, who asked him to undertake an expedition to New Guinea on behalf of himself and the American Museum of Natural History in New York. In New Guinea Mayr collected several thousands bird skins (he named 26 new bird species during his lifetime) and, in the process also named 38 new orchid species. During his stay in New Guinea, he was invited to accompany the Whitney South Seas Expedition to the Solomon Islands.

He returned to Germany in 1930 and in 1931 he accepted a curatorial position at the American Museum of Natural History, where he played the important role of brokering and acquiring the Walter Rothschild collection of bird skins, which was being sold in order to pay off a blackmailer. During his time at the museum he produced numerous publications on bird taxonomy, and in 1942 his first book, Systematics and the Origin of Species, which completed the evolutionary synthesis started by Darwin.

After Mayr was appointed at the American Museum of Natural History, he influenced American ornithological research by cultivating mentoring relationships with young birdwatchers. Mayr organized a monthly seminar under the auspices of the Linnaean Society of New York. This society, under the influence of J. A. Allen, Frank Chapman and Jonathan Dwight concentrated on taxonomy and later became a clearing house for bird banding and sight records.

There were a group of eight young birdwatchers from the Bronx and later became the Bronx County Bird Club and they were led by Ludlow Griscom. Mayr was surprised at the differences between American and German Birding Societies. He noted that the German society was "far more scientific, far more interested in life histories and breeding bird species, as well as in reports on recent literature."

Mayr also encouraged his Linnaean Society seminar participants to take up a specific research project of their own. "Everyone should have a problem" was the way one Bronx County Bird Club member recalled Mayr's refrain. One of Mayr's seminar participants was Joseph Hickey and under Mayr's influence went on to write A Guide to Birdwatching (1943). Hickey remembered later –"Mayr was our age and invited on all our field trips. The heckling of this German foreigner was tremendous, but he gave tit for tat, and any modern picture of Dr E. Mayr as a very formal person does not square with my memory of the 1930's.

He held his own." Mayr's said of his own involvement with the local birdwatchers: "In those early years in New York when I was a stranger in a big city, it was the companionship and later friendship which I was offered in the Linnean Society that was the most important thing in my life."

Another person that Mayr greatly influenced was Margaret Morse Nice. Mayr encouraged her to correspond with the European ornithologists of the time, and helped her in her landmark study on Song Sparrows. Nice wrote to Joseph Grinnell in 1932 trying to get foreign literature reviewed in the Condor: "Too many American ornithologists have despised the study of the living bird; the magazine[s] and books that deal with the subject abound in careless statements, anthropomorphic interpretations, repetition of ancient errors, and sweeping conclusions from a pitiful array of facts. ... in Europe the study of the living bird is taken seriously. We could learn a great deal from their writing." Mayr ensured that Nice could publish her two volume Studies in the Life History of the Song Sparrow, finding her a publisher, and her book was reviewed by Aldo Leopold, Grinnell, Jean Delacour. Nice dedicated her book to "My Friend Ernst Mayr."

Mayr joined the faculty of Harvard University in 1953, where he also served as director of the Museum of Comparative Zoology from 1961 to 1970. He retired in 1975 as emeritus professor of zoology, showered with honors. Following his retirement, he went on to publish more than 200 articles, in a variety of journals—more than some reputable scientists publish in their entire careers; 14 of his 25 books were published after he was 65. Even as a centenarian, he continued to write books. On his 100th birthday, he was interviewed by Scientific American magazine.

He received awards including the National Medal of Science, the Balzan Prize and the International Prize for Biology. He was never awarded a Nobel Prize, but he noted that there is no Prize for evolutionary biology, and that Darwin would not have received one, either.

Mayr was co-author of six global reviews of bird species new to science (listed below).

Mayr's ideas
As a traditionally trained biologist with little mathematical experience, Mayr was often highly critical of early mathematical approaches to evolution such as those of J. B. S. Haldane, famously calling in 1959 such approaches "bean bag genetics". He maintained that factors such as reproductive isolation had to be taken into account. In a similar fashion, Mayr was also quite critical of molecular evolutionary studies such as those of Carl Woese.

In many of his writings, Mayr rejected reductionism in evolutionary biology, arguing that evolutionary pressures act on the whole organism, not on single genes, and that genes can have different effects depending on the other genes present. He advocated a study of the whole genome rather than of isolated genes only. Current molecular studies in evolution and speciation indicate that although allopatric speciation seems to be the norm in groups (possibly those with greater mobility) such as the birds, there are numerous cases of sympatric speciation in many invertebrates (especially in the insects).

Mayr was an outspoken defender of the scientific method, and one known to sharply critique science on the edge. As a notable recent example, he criticized the search for aliens as conducted by fellow Harvard professor Paul Horowitz as being a waste of university and student resources, for its inability to address and answer a scientific question.