Support for systematics.
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Biological Evolution↗
Biomedical subjects
R T O'Grady
Publications and source records attributed to R T O'Grady.
Nonequilibrium thermodynamics and different axioms of evolution.
Proponents of two axioms of biological evolutionary theory have attempted to find justification by reference to nonequilibrium thermodynamics. One states that biological systems and their evolutionary diversification are physically improbable states and transitions, resulting from a selective process; the other asserts that there is an historically constrained inherent directionality in evolutionary dynamics, independent of natural selection, which exerts a self-organizing influence. The first, the Axiom of Improbability, is shown to be nonhistorical and thus, for a theory of change through time, acausal. Its perception of the improbability of living states is at least partially an artifact of closed system thinking. The second, the Axiom of Historically Determined Inherent Directionality, is supported evidentially and has an explicit historical component. Historically constrained dynamic populations are inherently nonequilibrium systems. It is argued that living, evolving systems, when considered to be historically constrained nonequilibrium systems, do not appear improbable at all. Thus, the two axioms are not compatible. Instead, the Axiom of Improbability is considered to result from an unjustified attempt to extend the contingent proximal actions of natural selection into the area of historical, causal explanations. It is thus denied axiomatic status, and the effects of natural selection are subsumed as an additional level of constraint in an evolutionary theory derived from the Axiom of Historically Determined Inherent Directionality.
Biological Evolution↗
Growth and form of the fourth-stage larvae and early adults of Ascaris suum Goeze, 1782 (Nematoda: Ascaridoidea) developing in pigs.
The fourth-stage larvae and adults of Ascaris suum were studied as they developed in the pig intestine from 11 to 22 days after infection. This is a period of rapid growth, in which both sexes increase approximately ten-fold in body length. Further examination of females showed the length increase to be positively allometric with respect to body diameter. The genital primordium in early fourth stage is at the same relative position along the length of the body as it is in the newly hatched larva. During development from fourth stage to adulthood the greater growth of the posterior part of the worm causes the relative position of the developing vulva to shift anteriad.
Animals↗
Evolutionary theory and teleology.
The order within and among living systems can be explained rationally by postulating a process of descent with modification, effected by factors which are extrinsic or intrinsic to the organisms. Because at the time Darwin proposed his theory of evolution there was no concept of intrinsic factors which could evolve, he postulated a process of extrinsic effects--natural selection. Biological order was thus seen as an imposed, rather than an emergent, property. Evolutionary change was seen as being determined by the functional efficiency (adaptedness) of the organism in its environment, rather than by spontaneous changes in intrinsically generated organizing factors. The initial incompleteness of Darwin's explanatory model, and the axiomatization of its postulates in neo-Darwinism, has resulted in a theory of functionalism, rather than structuralism. As such, it introduces an unnecessary teleology which confounds evolutionary studies and reduces the usefulness of the theory. This problem cannot be detected from within the neo-Darwinian paradigm because the different levels of end-directed activity--teleomatic, teleonomic, and teleological--are not recognized. They are, in fact, considered to influence one another. The theory of nonequilibrium evolution avoids these problems by returning to the basic principles of biological order and developing a structuralist explanation of intrinsically generated change. Extrinsic factors may affect the resultant evolutionary pattern, but they are neither necessary nor sufficient for evolution to occur.
Adaptation, Biological↗
The site selected by the larvae of Heligmosomoides polygyrus.
Histological examination of the small intestine of mice infected with Heligmosomoides polygyrus indicates that the final site of the larvae is in the circular muscle layer of the muscularis externa of the anterior small intestine. The larvae become embedded in the muscle between the first and third days after infection and are subsequently sequestered by a localized leucocytic response. There is no evidence of a true cyst. Histological evidence suggests that the larvae actively feed on the tissues of the host during their development.
Animals↗
Changes in the somatic musculature of the 4th-stage larvae of Ascaris suum Goeze, 1782 (Nematoda: Ascaridoidea) developing in swine.
Fourth-stage larvae of Ascaris suum, recovered from piglets at 11-22 days post-infection (p.i.), were examined by light microscopy for changes in the somatic musculature. During this time the estimated total number of muscle cells in the body increases from approximately 600 to 21 000 cells. This non-eutelic development appears to occur by division of platymyarian muscle cells into coelomyarian cells, thereby increasing the number of muscle cells/quadrant from 5 to 85. The incompleteness of these divisions results in sarcoplasmic connections among muscle cells, and between muscle cells and nerve chords. At 11 days p.i., immediately after the 3rd moult, the variation in muscle cell length in a quadrant, with the longest cells being at the lateral chords, has been established. The average muscle cell length at this point is 0.101 mm, the longest is 0.164 mm. These values have increased to 0.365 mm and 1.122 mm, respectively, by 22 days p.i. At 18 days p.i. those cells in the posterior section of the larva are still the shortest in the body.
Animals↗