Showing papers in "The Quarterly Review of Biology in 1969"

The evolution of hermaphroditism among animals

Abstract: Possible selective advantages, including some new ones, for hermaphroditism are reviewed It is proposed that hermaphroditism should evolve under the following conditions: (a) where it is hard to find a mate; (b) where one sex benefits from being larger or smaller than the other; or (c) where there are small, genetically isolated populations Some conceptual problems and a comparative means of study are discussed The literature is reviewed to show the conditions under which hermaphroditism may have evolved It is concluded that all thee explanations have some validity

The Recent Mammals of the Neotropical Region: A Zoogeographic and Ecological Review

Abstract: The Neotropical Region, which is defined on the basis of its living mammals, is comprised of the Brazilian, Patagonian, and West Indian Subregions. The Middle American Province of the Brazilian Subregion was the primary center of origin, evolution, and dispersal for mammals now living in continental South America. The West Indies also derived its fauna from Middle America, and perhaps also from South America. Faunal interchange between these regions must have taken place since the Middle Tertiary, at the latest. By the time the Isthmian land bridge between Middle and South America was completed during the Pliocene-Pleistocene transition, nearly all modern genera of Neotropical mammals were already differentiated within their present geographic ranges. Five faunal strata of Neotropical mammals are identified on the basis of postulated centers of origin of the ancestral stock, dispersal routes of colonizers, known grades of differentiation of living descendents, and the meager fossil evidence. The living fa...

The Ecology of Colonization as Seen in the Zoogeography of Anoline Lizards on Small Islands.

Abstract: One group of lizards-the iguanid genus Anolis in the West Indies-is now sufficiently well known to permit an empirical test of ecological theories of colonization in terms of these relatively slowly colonizing forms. Investigation of one special aspect-recent colonization of small distant islands-leads to the following conclusions: (1) Succesfully colonizing species are a small and specialized fraction of the number available for colonization. (2) They are "versatile" species-creatures of the ecotone, physiologically and ecologically tolerant of many conditions and requiring of few. (3) Below some critical island size a colonizing species may by ecological release exclude all congeners. In Anolis this size of island is large (e.g., 560 mi2). (4) Coexistence of colonists is possible either if they have been preadapted in sympatry and arrive nearly synchronously, or if the adaptations for coexistence are evolved in situ on complex island banks. (5) Some species have been modified by failed invasions. (6) Co...

Comparisons of the Contemporary Mammalian Faunas of the Southern Continents

Abstract: A group of papers on the mammalian faunas of Africa, the Neotropical region, and Australia (Quart. Rev. Biol., 43: 265-300; 373-408, 1968; 1-70, 1969) is reviewed from a comparative standpoint and certain general concepts relative to faunal evolution and distribution on those continents are developed. On the basis of current taxonomic information Africa has 51 families and 756 species of mammals, Neotropica 50 and 810, and Australia 18 and 364. If the section of Africa that has a rainfall of less than 5 inches per annum be excluded (the Sahara Desert covers almost one-third of the continent) the number of families and species per 100,000 square miles are comparable: Africa, 0.63 (9.39); Neotropica, 0.70 (11.3); Australia, 0.55 (11.03). Africa has the most diversified fauna. Neotropica owes its numerical richness to large faunas of rodents and bats. Stemming from their different basal stocks and different histories of isolation and faunistic interchange with adjacent continents, the three continents differ...

T. H. Morgan and the Emergence of a New American Biology

Abstract: At the turn of the twentieth century a number of the younger biologists (born after 1860) became dissatisfied with the prevailing interests and methods of research of their elders. An all-consuming interest in evolutionary relationships dominated many fields of biology, including embryology, cytology, genetics, paleontology, and taxonomy. Under the name of "general morphology," work was largely directed at elucidating phylogenetic relationships, often to the exclusion of legitimate problems in the various fields. The heavy emphasis on evolutionary considerations was largely European in origin, having spread to the United States through the many American biologists who were trained abroad in the early and middle nineteenth century. With the rise of American graduate education in the 1870's, a new generation of biologists began to escape the dominant European influences. Thomas Hunt Morgan (1866-1945) offers a good example of the attempt of younger men at this time to emancipate fields such as embryology, g...