Showing papers in "Evolutionary Biology-new York in 1983"
TL;DR: Attempts to assess the natural affinities and evolution of living crocodilians have been difficult and largely contradictory and morphoclines are rare, further complicating the efforts of the comparative morphologist.
Abstract: Attempts to assess the natural affinities and evolution of living crocodilians have been difficult and largely contradictory (Kalin, 1955; Steel, 1973; Dowling and Duellman, 1974). Morphological character analysis has been misleading due to the overall conservatism of these reptiles and to the tendencies toward parallelism and convergence of traits that has occurred during their evolution (Langston, 1973). These complications, together with the lack of critical fossils, have made paleontological interpretations extremely difficult (Sill, 1968; Hecht and Malone, 1972; Langston, 1973; Buffetaut, 1979). Because of such problems and the small number of living species, morphoclines are rare, further complicating the efforts of the comparative morphologist (Hecht and Malone, 1972).
101 citations
TL;DR: The creative force in evolution undoubtedly is not mutation pressure, but selection, and it had to be shown that steady selection pressure could slowly and gradually alter characters by accumulating small additive effects of many genes.
Abstract: There are good reasons why the importance of developmental biology for an understanding of evolution had to be rediscovered recently (Gould, 1977; Lovtrup, 1981; Bonner, 1982). The Synthetic Theory of Evolution had been built up on the demonstration that natural populations contain an immense amount of genetic variation that could fully account for the morphological variation studied by naturalists (Mayr and Provine, 1980). This central achievement of the Synthetic Theory had to be defended against a false picture of genetic evolution due to rare mutations with major, often deleterious effects. The creative force in evolution undoubtedly is not mutation pressure, but selection. To support this statement, the store of genetic variation in natural populations had to be characterized, and it had to be shown that steady selection pressure could slowly and gradually alter characters by accumulating small additive effects of many genes.
81 citations
TL;DR: Investigations of the cellular machinery have supplied striking evidence for the unity of life on earth, resulting from its common origin, and revealed the molecular basis of the genotype and its propagation.
Abstract: Molecular biology has brought a wealth of information in support of Darwin’s theory of natural selection. Investigations of the cellular machinery have supplied striking evidence for the unity of life on earth, resulting from its common origin, revealed the molecular basis of the genotype and its propagation, and shown the awesome complexity of its expression into the phenotype.
62 citations
TL;DR: The presence of genetic variation within populations is a prerequisite for adaptation and evolutionary change and a selective explanation for the maintenance of this variation must be sought.
Abstract: The presence of genetic variation within populations is a prerequisite for adaptation and evolutionary change. All genetic variation is ultimately generated through mutation. If a mutation has no effect on the fitness of individuals, the frequency of the mutant in the population will be determined by stochastic factors [a subject thoroughly dealt with by Wright (1969)]. On the other hand, where significant amounts of genetic variation affecting fitness are found in natural populations, a selective explanation for the maintenance of this variation must be sought.
53 citations
TL;DR: Two interests have merged in the study of the function and evolution of both interspecific and intraspecific enzyme variants and the possible roles the observed structural and functional variation might play in adaptation.
Abstract: In the last two decades the study of adaptation at the molecular level has become a rapidly growing part of evolutionary biology. Some of the impetus for this interest has come from the largely unconvincing attempts to explain the existence and patterns of structural diversity of homologous proteins, especially enzymes, within and among plant and animal species (Lewontin, 1974; Nei, 1975; Wilson et al., 1977; Ayala et al., 1976). Additional motivation has come from comparative physiology and the need to understand the molecular basis of physiological adaptation to different environments. These two interests have merged in the study of the function and evolution of both interspecific and intraspecific enzyme variants and the possible roles the observed structural and functional variation might play in adaptation.
41 citations
Journal Article•
TL;DR: Two major schools of thought exist regarding macroevolution, one favoring gradual evolution, the other saltation as discussed by the authors, which is based on the accumulation over a long period of time of small mutations, while the latter is considered to occur relatively rapidly as to the result of the isolation of peripheral populations that have undergone large-magnitude mutations and have been filtered by natural selection.
Abstract: Although a general concordance has been achieved concerning the mechanisms underlying evolution at the intraspecific level, transspecific evolution is still a controversial and quite intriguing issue. The controversy is caused by the relatively short time span in which higher taxa evolved and the rarity or lack of morphological intermediates in the fossil record. Two major schools of thought exist regarding macroevolution, one favoring gradual evolution, the other saltation. The former process is based on the accumulation over a long period of time of small mutations, while the latter is considered to occur relatively rapidly as to the result of the isolation of peripheral populations (Mayr, 1942, 1954, 1982) that have undergone large-magnitude mutations [in the extreme case, Goldschmidt’s (1940) “hopeful monsters”] and have been filtered by natural selection (Eldredge and Gould, 1972; Gould, 1977). The history and details of these concepts are discussed by Mayr (1982).
37 citations
TL;DR: A preference for mating with a member of one’s own species (ethological isolation) is a necessary feature common to all congeneric species pairs living in sympatry.
Abstract: Closely related species—for example, members of the same genus often coexist within small geographic areas. Drosophila pseudoobscura and D. persimilis can serve as a familiar example. Although their geographic distributions differ (Dobzhansky and Epling, 1944), as do their local spatial, feeding, and temporal preferences (Dobzhansky, 1951; Dobzhansky et al., 1956), members of these two species do nevertheless encounter one another where they occur sympatrically. They can, for example, be taken in the same trap. There, mating flies can be frequently observed, but when females are distributed individually among culture bottles, hybrid progeny are rarely encountered. Dobzhansky et al. (1968) report that among several thousand progenies examined over several decades, only two were of hybrid origin. [Reasons for believing that gene exchange between these species may be even rarer than these two cases would suggest are given by Dobzhansky (1951, 1973).] A preference for mating with a member of one’s own species (ethological isolation) is a necessary feature common to all congeneric species pairs living in sympatry.
11 citations