Ornithology, Evolution, and Philosophy 123

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A Modern Unified Theory of Evolution 215 Fig.5.4. Twosetsofspeciesandsubspeciestaxaeachofwhichformsonelargecontinental unit (left) and several geographically isolated populations (right) with their hypothetical cladograms. Schematic representation. H hybrid zone between subspecies, P parapatric contact zone between species (geographic exclusion without or nearly without hybridization). In the cladograms hatching indicates known intergradation (hybridization), dashes indicate presumed hybridization. In all areas the respective sympatric populations (taxa) of these two sets are specifically distinct with respect to each other (biological species). In the upper set, forms a and b hybridize and together represent species 1 which does not hybridize with parapatric species 2 (consisting of subspecies c and d). The status of the island populations d–f as species or subspecies (i.e., their hybridization or non-hybridization if they were in contact) is judged on the basis of inference (see text). Because forms alpha and beta of the lower assemblage hybridize freely where they meet, forms gamma and delta are also assumed to hybridize if they would establish contact. All four taxa are considered subspecies of one polytypic species. Species 1 to 4 are all monophyletic (1) degree of difference between sympatric species, (2) degree of difference between intergrading subspecies within widespread species, (3) degree of difference between hybridizing populations in related species. Occasional criticisms of the biological species concept refer mostly to its practical application in delimiting species taxa rather than to the theoretical notion of biological species itself. The highlights of Mayr’s views on the Biological Species Concept, as expressed again in several recent articles (1988h, 1996e, 2000e), may be summarized as follows: A biological species is a reproductively (genetically) cohesive assemblage of populations, an assemblage of well-balanced harmonious genotypes. The devices which
216 5 Biological Species and Speciation—Mayr’s First Synthesis maintain the integrity of species, protecting the harmonious gene pools, are isolating mechanisms, a term proposed by Dobzhansky (1935, 1937: 228–258) who, unfortunately, did not distinguish between external geographical/ecological barriers operating in the allopatric phase of speciation and intrinsic mechanisms. Mayr (1963b: 89–109) stressed the enormous diversity of these devices, e.g., sterility genes, chromosomal incompatibilities, ecological exclusion, behavioral properties especially in higher animals. Species usually occupy ecological niches that are sufficiently different to permit the sympatric occurrence of these species. However, member species of a superspecies exclude one another allo- or parapatrically because of ecological competition. The Biological Species Concept is not applicable to asexual organisms (agamospecies) which form clones, not interbreeding populations, as defined by the biologist. Their gene pools do not require protection by isolating mechanisms, because they usually are not subject to genetic recombination. A list of Mayr’s publications dealing with the species problem totals 94. Allopatric Speciation Evolutionists understood since the “Fisherian synthesis” (p. 183) how and why populations of species change over time, yet species are distinct–they do not hybridize with or blend into one another. How can one separate species arise from another (parental) species or one species split into two? Some geneticists (“saltationists” like W. Bateson, H. de Vries, R. Goldschmidt) believed that new species arise instantaneously by large mutations, sudden steps in which either a single character or a whole set of characters together become changed. By contrast, the naturalists were “gradualists” and believed that speciation is a populational process, a gradual accumulation of small changes often by natural selection. To solve the apparent contradiction between sympatric species of a local fauna separated by bridgeless gaps on one hand and the idea of gradual speciation on the other hand Mayr presented many intermediate “borderline cases” of geographic variation from his work on the birds of Oceania pointing to a gradual origin of new species from isolated (peripheral) groups of populations of an ancestral species (1940c, 1942e, 1951l, 1963b). The differences he observed among representative island populations were not only quantitative and continuous but often qualitative and discrete as observed among congeneric species. For these reasons he replaced the typological concept of species by a concept of species taxa as aggregates of geographically variable populations. “What I did, basing my conclusions on a long tradition of European systematics, was to introduce the horizontal (geographical) dimension, and show that the process of geographic speciation is the method by which a gradual evolution of new species is possible, in spite of the gaps in the non-dimensional situation” (Mayr 1992i: 7). As he stated in this quote and in other historical reviews (p. 230), the principles of the biological species concept and of allopatric speciation had long been
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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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96 3 The New York Years (1931-1953)
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98 3 The New York Years (1931-1953)
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100 3 The New York Years (1931-1953
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4 Ornithologist and Zoogeographer B
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142 4 Ornithologist and Zoogeograph
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Page 169 and 170: 164 4 Ornithologist and Zoogeograph
Page 189 and 190: 184 5 Biological Species and Specia
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8 Evolutionary Biology— Mayr’s
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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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286 9 Ernst Mayr—the Man addresse
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288 9 Ernst Mayr—the Man undertak
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290 9 Ernst Mayr—the Man unaware
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292 9 Ernst Mayr—the Man His hand
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294 9 Ernst Mayr—the Man Prize (1
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296 9 Ernst Mayr—the Man the inte
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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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