VMartin
Posts: 525 Joined: Nov. 2006
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From the history criticising professor Portmann's concept of descent of testicles.
As far as I know professor Adolf Portmann's book Spirit and biology (Geist und Biologie) has never been translated into English. Yet professor Portmann's concept of descent of testicles was criticized heavily in neodarwinian journal Evolution published by Society for the Study of Evolution (can be find at jstor) in 1958.
In the "THE EVOLUTIONARY SIGNIFICANCE OF THE SCROTUM" by Raymond Cowles we can read about cooling of birds spermatozoa:
Quote | In summary it seems probable that in the aves we have a case of vertebrates, having high normal body temperatures and no external thermal regulatory scrotum, substituting for this device a system that requires nocturnal spermatogenesis when temperatures are regularly 2-3" C. below the daytime norm and that in addition there is direct ventilation and a 2-3" C. cooling in the air sac that partly or wholly insulates the testes from the viscera and the kidney with its massive blood flow, while permatogenesis is in progress, and that in addition sperms may be stored in an external protuberance carrying a convoluted portion of the vas deferens. Surely there is evidence here that does not agree with Portmann's dismissal of the importance of temperature in reproduction. Portmann's unwillingness to accept the extensive experimental work that has been done in this field since at least as early as 1898 and continuing to the present, and his substitution of an "all or none" speculation based solely on the gaudy posteriors of apes and the ornamented posteriors of some Artiodactyles is less than convincing.
Whether or not Cowles' hypothetical involvement of heat sterility and associated phenomena will prove to be correct in all respects is a matter for others to say but because of the possible importance of heat susceptibility in the spermatogenic process, it is indeed unfortunate that in order to support his concept, Portmann is not even willing to concede the correctness of the conclusions of literally scores of workers.
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and Rodolfo Ruibal Uni California in the same journal:
THE EVOLUTION OF THE SCROTUM
Quote | Direct evidence has been provided by Riley (1937) to show that avian spermatogenesis is sensitive to high temperatures....However, when the birds become active and raise the body tetnperautre to 110' F. there is a complete cessation of spermatogenesis. It is clear that instead of contradicting the thermoregulatory theory, the avian condition does provide corroboration, since there is evidence of some analogous adaptation.
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Pretty convincing and self-confident neodarwinian stuff, isn't it? Yet the reality seems to be different than neodarwinists would like to have it:
Determination of Testis Temperature Rhythms and Effects of Constant Light on Testicular Function in the Domestic Fowl (Gallus domesticus)
Christine E. Beaupre, 3 ,5 Corinna J. Tressler,4 ,5 Steven J. Beaupr6,6 James L.M. Morgan,5 Walter G. Bottje,5 and John D. Kirby2,5
Center of Excellence for Poultry Science, Departments of Poultry Sciences and Biological Sciences
Quote | It is apparent from the data that the testis is not cooled by association with an air sac and, indeed, is not cooled by any mechanism. Therefore, spermatogenesis occurs in the domestic fowl at the core body temperature of 40-41 C. Our results provide evidence for the uniqueness of spermatogenesis in the avian testis as compared to that of the mammals examined thus far, in which spermatogenesis occurs at 33-350 C.
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and authors ask:
Quote | Our data raise interesting questions relative to reproductive fitness and evolution. For example, why have most mammals evolved external (and cooler) testes, which makes the testes (and most importantly, the genetic potential they contain) much more vulnerable, while the other predominant homeothermic group, Aves, have evolved testes that function efficiently at elevated core body temperatures?
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http://www.biolreprod.org/cgi/reprint/56/6/1570.pdf
-------------- I could not answer, but should maintain my ground.-
Charles Darwin
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