From Anomaly to Unification: Tracy Sonneborn and the Species Problem in Protozoa, 1954--1957 |
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Authors: | Judy Johns Schloegel |
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Institution: | (1) Avenue Parmentier 2A, B-1150 Brussels, Belgium |
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Abstract: | This article examines the critique of the biological species concept advanced by protozoan geneticist Tracy Sonneborn at the
1955 AAAS symposium on “the species problem,” published subsequently in 1957. Although Sonneborn was a strong proponent of
a population genetical conception of species, he became critical of the biological species concept for its failure to incorporate
asexual and obligatory inbreeding organisms. It is argued that Sonneborn's intimate knowledge of the ciliate protozoan Paramecium
aurelia species complex brought him into conflict with a growing pressure in the biological sciences to emphasize universal
principles of life. Faced with the need to defend the value of P. aurelia as an investigative tool, Sonneborn argued that
the sharp break in nature between sexual and asexual organisms posited by proponents of the biological species concept was
not an existential feature of the living world, but rather the misleading consequence of an operational definition of species
based only upon sexual organisms. Drawing upon his knowledge of the immense variability of P. aurelia, he proposed instead
a continuum of breeding systems from obligatory outbreeding to asexual organisms, and a more broadly unifying definition of
species that incorporated asexual as well as sexual organisms. Paradoxically, the push for unification that then characterized
the evolutionary synthesis served to debar critical consideration of Sonneborn's more unificatory alternative, and his underlying
contention that biological anomaly could serve as an important source of conceptual unification.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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Keywords: | biological species concept evolution--twentieth century evolutionary synthesis intimate knowledge model organisms protozoa Tracy Sonneborn species problem/kwd> |
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