Although Charles Darwin and others posited that multiple species could evolve from a single common ancestor, the mechanism by which this occurred was not understood, creating the species problem. Ernst Mayr approached the problem with a new definition for species. In his book Systematics and the Origin of Species (1942) he wrote that a species is not just a group of morphologically similar individuals, but a group that can breed only among themselves, excluding all others. When populations within a species become isolated by geography, feeding strategy, mate choice, or other means, they may start to differ from other populations through genetic drift and natural selection, and over time may evolve into new species. The most significant and rapid genetic reorganization occurs in extremely small populations that have been isolated (as on islands).
Mayr was the second son of Helene Pusinelli and Dr. Otto Mayr. His father was a jurist (District Prosecuting
Attorney at Würzburg) but took an interest in natural history and took the children out on field trips. He learnt all the local birds in Würzburg from his elder brother Otto. He also had access to a natural history magazine for amateurs, Kosmos. His father died just before he was thirteen. The family then moved to Dresden and he studied at the Staatsgymnasium ("Royal Gymnasium" until 1918) in Dresden-Neustadt and completed his high school education there. In April 1922, while still in high school, he joined the newly founded Saxony Ornithologists' Association. Here he met Rudolf Zimmermann, who became his ornithological mentor. In February 1923, Mayr passed his high school examination (Abitur) and his mother rewarded him with a pair of binoculars.
On 23 March 1923 on the lakes of Moritzburg, the Frauenteich, he spotted what he identified as a red-crested pochard. The species had not been seen in Saxony since 1845 and the local club argued about the identity. Raimund Schelcher (1891-1979) of the club then suggested that Mayr visit his classmate Erwin Stresemann on his way to Greifswald, where Mayr was to begin his medical studies. After a tough interrogation, Stresemann accepted and published the sighting as authentic. Stresemann was very impressed and suggested that, between semesters, Mayr could work as a volunteer in the ornithological section of the museum. Mayr wrote about this event, "It was as if someone had given me the key to heaven." He entered the University of Greifswald in 1923 and, according to Mayr himself, "took the medical curriculum (to satisfy a family tradition) but after only a year, he decided to leave medicine and enrolled at the Faculty of Biological Sciences." Mayr was endlessly interested in ornithology and "chose Greifswald at the Baltic for my studies for no other reason than that ... it was situated in the ornithologically most interesting area." Although he ostensibly planned to become a physician, he was "first and foremost an ornithologist." During the first semester break Stresemann gave him a test to identify treecreepers and Mayr was able to identify most of the specimens correctly. Stresemann declared that Mayr "was a born systematist". In 1925, Stresemann suggested that he give up his medical studies, in fact he should leave the faculty of medicine and enrol into the faculty of Biology and then join the Berlin Museum with the prospect of bird-collecting trips to the tropics, on the condition that he completed his doctoral studies in 16 months. Mayr completed his doctorate in ornithology at the University of Berlin under Dr. Carl Zimmer, who was a full professor (Ordentlicher Professor), on 24 June 1926 at the age of 21. On 1 July he accepted the position offered to him at the museum for a monthly salary of 330.54 Reichsmark.
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 thousand 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. Also, while in New Guinea, he visited the Lutheran missionaries Otto Thiele and Christian Keyser, in the Finschhafen district; there, while in conversation with his hosts, he uncovered the discrepancies in Hermann Detzner's popular book Four Years Among the Cannibals in German Guinea from 1914 to the Truce, in which Detzner claimed to have seen the interior, discovered several species of flora and fauna, while remaining only steps ahead of the Australian patrols sent to capture him.
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 mentoring young birdwatchers. 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 organized a monthly seminar under the auspices of the Linnean Society of New York. Under the influence of J.A. Allen, Frank Chapman, and Jonathan Dwight, the society concentrated on taxonomy and later became a clearing house for bird banding and sight records.
Mayr encouraged his Linnaean Society seminar participants to take up a specific research project of their own. Under Mayr's influence one of them, Joseph Hickey, 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 1930s. He held his own." A group of eight young birdwatchers from The Bronx later became the Bronx County Bird Club, led by Ludlow Griscom. "Everyone should have a problem" was the way one Bronx County Bird Club member recalled Mayr's refrain.
Mayr 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."
Mayr also greatly influenced the American ornithologist Margaret Morse Nice. Mayr encouraged her to correspond with European ornithologists 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 magazines 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. He found her a publisher, and her book was reviewed by Aldo Leopold, Joseph Grinnell, and 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. Mayr died on 3 February 2005 in his retirement home in Bedford, Massachusetts after a short illness. His wife, Margarete, died in 1990. He was survived by two daughters, five grandchildren and 10 great-grandchildren.
Mayr said he was an atheist in regards to "the idea of a personal God" because "there is nothing that supports [it]"
As a traditionally trained biologist, Mayr was often highly critical of early mathematical approaches to evolution such as those of J.B.S. Haldane, famously calling such approaches "beanbag genetics" in 1959. 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. Current molecular studies in evolution and speciation indicate that although allopatric speciation is the norm, there are numerous cases of sympatric speciation in groups with greater mobility (such as birds). The precise mechanisms of sympatric speciation, however, are usually a form of microallopatry enabled by variations in niche occupancy among individuals within a population.
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. After articulating the biological species concept in 1942, Mayr played a central role in the species problem debate over what was the best species concept. He staunchly defended the biological species concept against the many definitions of "species" that others proposed.
The funny thing is if in England, you ask a man in the street who the greatest living Darwinian is, he will say Richard Dawkins. And indeed, Dawkins has done a marvelous job of popularizing Darwinism. But Dawkins' basic theory of the gene being the object of evolution is totally non-Darwinian. I would not call him the greatest Darwinian.
Mayr insisted that the entire genome should be considered as the target of selection, rather than individual genes:
The idea that a few people have about the gene being the target of selection is completely impractical; a gene is never visible to natural selection, and in the genotype, it is always in the context with other genes, and the interaction with those other genes make a particular gene either more favorable or less favorable. In fact, Dobzhansky, for instance, worked quite a bit on so-called lethal chromosomes which are highly successful in one combination, and lethal in another. Therefore people like Dawkins in England who still think the gene is the target of selection are evidently wrong. In the 30s and 40s, it was widely accepted that genes were the target of selection, because that was the only way they could be made accessible to mathematics, but now we know that it is really the whole genotype of the individual, not the gene. Except for that slight revision, the basic Darwinian theory hasn't changed in the last 50 years.
New Ireland Rail - Hypotaenidia ernstmayri+ (Kirchman & Steadman, 2006)  - a relatively large, probably flightless, extinct rail, family Rallidae, known from subfossil remains found on prehistoricarcheological sites, in caves on New Ireland, in the Bismarck Archipelago, western Oceania. (Although described in the genus Gallirallus, this species is now placed in Hypotaenidia.)
Star Mountains Worm-eating Snake - Toxicocalamus ernstmayriO'Shea, Parker & Kaiser, 2015  - a 1.2 m, rare and secretive, venomous snake from the family Elapidae, believed to feed exclusively of earthworms, particularly the giant earthworms of the Megascolecidae. The etymology reads: The species name ernstmayri is a patronym honoring the German-American ornithologist, systematist, and evolutionary thinker Ernst Mayr (1904-2005). There are several connections linking Ernst Mayr to this new species of Toxicocalamus, which make him, and this snake, the ideal candidates for a patronym. First, Mayr himself visited New Guinea, and during the late 1920s he spent over 2 years conducting fieldwork in an area now part of PNG, as a member of a joint Rothschild-AMNH expedition focusing on birds of paradise (Aves, Passeriformes, Paradisaeidae), during which he collected many new bird and orchid species. Second, the holotype of T. ernstmayri has been housed in the MCZ collection, mislabeled as Micropechis ikaheka, after having arrived and been accessioned in June 1975, the month and year that Mayr retired. Third, the true identity of this specimen was recognized by one of us (MOS) during a visit to the MCZ in May 2014, undertaken with the financial support of an Ernst Mayr Travel Grant from Harvard University, awarded to enable examination of the Toxicocalamus holdings at the MCZ and the AMNH, the two U.S. institutions where Mayr worked. Finally, 2015, the publication year of this description, marks the decennial of Mayr's passing at age 100, and naming a New Guinea snake after him seems a suitable tribute.
Individuals less suited to the environment are less likely to survive and less likely to reproduce; individuals more suited to the environment are more likely to survive and more likely to reproduce and leave their heritable traits to future generations, which produces the process of natural selection (fact).
This slowly effected process results in populations changing to adapt to their environments, and ultimately, these variations accumulate over time to form new species (inference).
In relation to the publication of Darwin's Origins of Species, Erst Mayr identified philosophical implications of evolution:
An evolving world, not a static one.
The implausibility of creationism.
The refutation that the universe has purpose.
Defeating the justifications for a human-centric world.
Materialistic processes explain the impression of design.
1946 "The naturalist in Leidy's time and today". Proceedings of the Academy of Natural Sciences of Philadelphia 98:271-276
1947 "Ecological factors in speciation". Evolution 1:263-288
1948 "The new Sanford Hall". Natural History 57:248-254
1950 The role of the antennae in the mating behavior of female Drosophila. Evolution 4:149-154
1951 Introduction and Conclusion. Pages 85,255-258 in The problem of land connections across the South Atlantic with special reference to the Mesozoic. Bulletin of the American Museum of Natural History 99:79-258
1951 with Dean Amadon, "A classification of recent birds". American Museum Novitates no. 1496
1953 with E G Linsley and R L Usinger. Methods and Principles of Systematica Zoology. McGraw-Hill, New York.
1954 "Changes in genetic environment and evolution". Pages 157-180 in Evolution as a Process (J Huxley, A C Hardy and E B Ford Eds) Allen and Unwin. London
1955 "Karl Jordan's contribution to current concepts in systematics and evolution". Transactions of the Royal Entomological Society of London 107:45-66
1956 with C B Rosen. "Geographic variation and hybridization in populations of Bahama snails (Cerion)". American Museum Novitates no 1806.
1957 "Species concepts and definitions". Pages 371-388 in The Species Problem (E. Mayr ed). AAAS, Washington DC.
1959 "The emergence of evolutionary novelties". Pages 349-380 in The Evolution of Life: Evolution after Darwin, vol 1 (S. Tax, ed) University of Chicago.
1959 "Darwin and the evolutionary theory in Biology". Pages 1-10 in Evolution and Anthropology: A Centennial Appraisal (B J Meggers, Ed) The Anthropological Society of Washington, Washington DC.
1959 "Agassiz, Darwin, and Evolution". Harvard Library Bulletin. 13:165-194
1961 "Cause and effect in biology: Kinds of causes, predictability, and teleology are viewed by a practicing biologist". Science 134:1501-1506
1962 "Accident or design: The paradox of evolution". Pages 1-14 in The Evolution of Living Organisms (G W Leeper, Ed) Melbourne University Press.
1964 Introduction, Bibliography and Subject Pages vii-xxviii, 491-513 in On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life, by Charles Darwin. A Facsimile of the First Edition. Harvard University Press.
1965 Comments. In Proceedings of the Boston Colloguium for the Philosophy of Science, 1962-1964. Boston Studies in the Philosophy of Science 2:151-156
1969 Discussion: Footnotes on the philosophy of biology. Philosophy of Science 36:197-202
1972 Continental drift and the history of the Australian bird fauna. Emu 72:26-28
1972 Geography and ecology as faunal determinants. Pages 549-561 in Proceedings XVth International Ornithological Congress (K H Voous, Ed) E J Brill, Leiden, The Netherlands.
1972 Lamarck revisited. Journal of the History of Biology. 5:55-94
1980 How I became a Darwinian, Pages 413-423 in The Evolutionary Synthesis (E Mayr and W Provine, Eds) Harvard University Press, Cambridge, Massachusetts.
1980 with W B Provine, Eds. The Evolutionary Synthesis. Harvard University Press.
1981 Evolutionary biology. Pages 147-162 in The Joys of Research (W. Shripshire Jr, Ed.) Smithsonian Institution Press.
1984 Evolution and ethics. Pages 35-46 in Darwin, Mars and Freud: Their influence on Moral Theory (A L Caplan and B Jennings, Eds.) Plenum Press, New York.
1985. Darwin's five theories of evolution. In D. Kohn, ed., The Darwinian Heritage, Princeton NJ: Princeton University Press, pp. 755-772.
1985. How biology differs from the physical sciences. In D. J. Depew and B H Weber, eds., Evolution at a Crossroads: The New Biology and the New Philosophy of Science, Cambridge MA: The MIT Press, pp. 43-63.
1988. The why and how of species. Biology and Philosophy 3:431-441
1992. The idea of teleology. Journal of the History of Ideas 53:117-135
1994. with W.J. Bock. Provisional classifications v. standard avian sequences: heuristics and communication in ornithology. Ibis 136:12-18
^Kirchman, J.J.; Steadman, D.W. (2006). "Rails (Rallidae: Gallirallus) from prehistoric archaeological sites in Western Oceania". Zootaxa. 1316: 1-31. doi:10.5281/zenodo.173941.
^Hume, J.P., 2017, Extinct Birds (2nd edition). Bloomsbury Natural History. 576 pp. ISBN978-1472937445.
^O'Shea, M.; Parker, F.; Kaiser, H. (2015). "A new species of New Guinea Worm-eating Snake, genus Toxicocalamus (Serpentes: Elapidae), from the Star Mountains of Western Province, Papua New Guinea, with a revised dichotomous key to the genus". Bulletin of the Museum of Comparative Zoology. 161 (6): 241-264. doi:10.3099/0027-4100-161.6.241.
^Kulkarni, S.; Ghate, H.V. (2016). "A new cavernicolous assassin bug of the genus Bagauda Bergroth (Heteroptera: Reduviidae: Emesinae) from the Western Ghats, India". Zootaxa. 4127 (2): 365-375. doi:10.11646/zootaxa.4127.2.8. PMID27395629.