Joined: Nov. 2006
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:
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
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.
and Rodolfo Ruibal Uni California in the same journal:
THE EVOLUTION OF THE SCROTUM
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.
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
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.
and authors ask:
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?
I could not answer, but should maintain my ground.-