3 The New York Years (1931–1953)

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218 5 Biological Species and Speciation—Mayr’s First Synthesis Fig.5.5. Stages of geographical (allopatric) speciation (from Mayr 1942e, Fig. 16) found which were difficult to classify (see Table 4.2 on p. 177). However, such “intermediate” forms illustrated for Mayr the process of speciation graphically. Strictly speaking it is not the subspecies but the geographically isolated population which may reach species status. However, little was known about the genetic basis of the speciation process itself which both Dobzhansky (1937) and Mayr (1942e) felt certain occurred as a continuation of microevolution. In a superspecies the member species are not ecologically compatible, for which reason the respective species populations, if their ranges abut, compete along the contact zones and exclude each other geographically without (or only rarely) hybridizing. The closely related members of a species group may be sympatric in parts of their ranges. In ring species the overlapping populations are so strongly differentiated that they no longer hybridize and would be considered species if their direct intergradation through the “ring” of subspecies were to be interrupted (an example are the Asian greenish warblers Phylloscopus trochiloides, Irwin et al. 2005). According to the “Wallace-Dobzhansky model” isolating mechanisms of neospecies originate due to selection forces in sympatry, whereas according to the “Darwin-Muller-Mayr model” isolating mechanisms arise as incidental, pleiotropic by-products of divergence in allopatry (but see also under sympatric speciation, p. 223). David Lack (1944, 1949, 1971) added important data on ecological aspects of the speciation process, as acknowledged by Mayr (1982d: 274). Besides the “dumbbell” model of geographic speciation, Mayr (1942e) developed an alternative speciation model: a new species originates from jump dispersal of a few individuals forming a small strongly isolated peripheral founder population (founder principle, 1942e: 237; 1954c; 1963b: 539, 554; peripatric speciation, 1982l). This principle relates the reduced variability of small founder populations not to accidental gene loss, but to the fact that the entire population was started by a single pair, a few individuals or even by one fertilized female which contained only a fraction of the gene pool of the parent population. These “founders” carried
A Modern Unified Theory of Evolution 219 with them only a very small proportion of the genetic variability of the parent population. This idea goes back to an early formulation by Rensch (1939: 184) who, however, did not appreciate its importance. He emphasized (transl.) that “the gene pool of a few individuals [establishing a new island population] never corresponds to the total gene pool of the numerous individuals of the parent population. In such cases the newly developing island race is not characterized by an increase but byadecreaseofgenes” (italics in the original). In a later article on “Change of genetic environment and evolution” (which he considered as one of his most important publications) Mayr (1954c) discussed the genetic processes during speciation of peripherally isolated founder populations. His main idea was that in the limited gene pool the selective value of the genes would be different from the original condition in the parent population particularly owing to inbreeding and a rise in homozygosity. Later the population will enlarge and gradually build up its depleted genetic variability. Rapid evolution in founder populations may lead to the development of strongly differentiated bizarre peripheral isolates (p. 158). Such forms, however, have low evolutionary success, when subsequently exposed to competition with mainland stocks. Mayr did not claim, however, that every founder population speciates, that every genetic change in a founder population is a genetic revolution or that speciation occurs only in founder populations. On the other hand, he was already fully aware of the consequences of his theory pointing out that geographical isolation and the small size of speciating founder populations may explain the phenomenon of lack of documentation of speciation in the fossil record. As he stated, “Many paleontologists have postulated various kinds of typostrophic ‘saltations’ in order to explain the absence of crucial steps from the fossil record. If these changes have taken place in small peripheral isolated populations, it would explain why they are not found by paleontologists” (1954c: 210). Many years later the paleontologists Eldredge and Gould (1972) based their theory of “punctuated equilibrium” on Mayr’s observations. Although they did refer to his relevant publications, this intellectual debt got almost lost in later years. In developing his model of genetic revolutions during the speciation process Mayr (1954c) applied the “new genetics” of Dobzhansky, Wallace and others who like Wright emphasized the interaction of genes and their varying selective values depending on their “genetic environment” or “genetic background.” Mayr (l.c.) introduced these latter terms which were widely appreciated and applied in discussions of the integration of the gene pool or of coadaptation among genes (Williams 1966: 59). Mayr got the idea of “genetic reorganization” (or “genetic revolution”) in peripherally isolated populations when visiting Naples, Italy during the summer of 1951 and lectured on it already in Oxford during September of that year. At that time, E. B. Ford asked him to contribute a paper on this topic to a festschrift for Julian Huxley which only appeared 3 years later. Until then Mayr was “mortally afraid that someone else would get ahead of me.” In retrospect Mayr commented on his idea of “genetic revolutions” during speciation in an interview as follows: “I still think that this is an important idea. The key thing is that the smaller the population, the more important the chance
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Jürgen Haffer Ornithology, Evoluti
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Jürgen Haffer Ornithology, Evoluti
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Preface Ernst Mayr (1904-2005), emi
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Contents Introduction 1 Part I The
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Contents IX 2 Bibliography of Ernst
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2 Introduction and speciation, the
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4 Introduction (1928-1929) to repla
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Ernst Mayr has been an observer all
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The Family 9 court system. He had a
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The Family 11 Fig.1.1. Family genea
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The Family 13 where they learned La
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Birdwatching 15 even finishing befo
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Birdwatching 17 Fig.1.5. ErnstMayr
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Birdwatching 19 Fig.1.6. Ernst Mayr
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Birdwatching 21 he simply smoked ci
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University Student in Greifswald an
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Friendships at School and Universit
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2 The Budding Scientist PhD Thesis
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TheInfluenceofTeachers 37 excellent
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Erwin Stresemann—Teacher and Frie
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Erwin Stresemann—Teacher and Frie
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Assistant Curator at the Museum of
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Expeditions to New Guinea and the S
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Part II Ornithologist and Evolution
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4 Ornithologist and Zoogeographer B
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142 4 Ornithologist and Zoogeograph
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Page 262 and 263: Part III Professor of Zoology at Ha
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268 8 Evolutionary Biology—Mayr
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284 9 Ernst Mayr—the Man his coll
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298 9 Ernst Mayr—the Man I have s
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300 9 Ernst Mayr—the Man Fig.9.4.
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302 9 Ernst Mayr—the Man not mali
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304 9 Ernst Mayr—the Man papers d
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306 9 Ernst Mayr—the Man 2005. Me
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308 9 Ernst Mayr—the Man Fig.9.5b
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310 9 Ernst Mayr—the Man health i
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312 9 Ernst Mayr—the Man person a
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314 9 Ernst Mayr—the Man with a r
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316 9 Ernst Mayr—the Man conceptu
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318 9 Ernst Mayr—the Man the two
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10 Systematics and Classification T
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322 10 Systematics and Classificati
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11 History and Philosophy of Biolog
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340 11 History and Philosophy of Bi
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376 12 Summary: Appreciation of Ern
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Acknowledgments Iamdeeplygratefulto
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List of Abbreviations AAAS American
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386 References Beehler BM, Pratt TK
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388 References Cracraft J (2002) Go
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390 References Haffer J (1997a) Ess
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392 References Keast JA (1996) Avia
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394 References Olson SL (1975) The
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396 References Smith JJ (1936) Eric
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398 References Wiglesworth LW (1898
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Appendix 1 Curriculum Vitae (includ
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Appendix 1 403 1978 Prêmio Jabuti,
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Appendix 1 405 Society Offices Linn
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Appendix 2 407 1926c Das Freibrüte
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Appendix 2 409 1932 1932a Birds col
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Appendix 2 411 1936g Melidectes bel
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Appendix 2 413 1941e Birds collecte
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Appendix 2 415 1944f Chromosomes an
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Appendix 2 417 1947g On the correct
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Appendix 2 419 1952e Six new subspe
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Appendix 2 421 1954g The tail molt
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Appendix 2 423 1958c Concluding rem
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Appendix 2 425 in E. Mayr, Evolutio
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Appendix 2 427 1964l Introduction [
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Appendix 2 429 1967d Subfamily Pach
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Appendix 2 431 in Acta Soc. Zool. B
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Appendix 2 433 1974b The diversity
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Appendix 2 435 1976m Evolution and
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Appendix 2 437 Mankind 13:430; P.W.
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Appendix 2 439 (1984) in Queen’s
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Appendix 2 441 1984c Evolution and
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Appendix 2 443 1987b The status of
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Appendix 2 445 1990 1990a The Myth
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Appendix 2 447 1992f Haldane’s Ca
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Appendix 2 449 1995g The search for
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Appendix 2 451 1999 1999a Thoughts
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List of Books by Ernst Mayr 453 200
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Coauthorship 455 Coauthorship In th
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Appendix 3 457 (4) Systematics 1942
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Index Achievements 379 Adaptation 2
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Index 461 Faunas 164-165 Family 8-1
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Index 463 Realism and education 372
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