Integration and dissociability in the development of specializations in Sauropsida
Slabý, O.
Folia Morphologica 34(4): 439-448
1986
ISSN/ISBN: 0015-5640 PMID: 3804101 Document Number: 278091
The specialized nasal apparatus of Sauropsida evolved-like other specialized organs-through the interaction and integration of a few constant specialized components, which occupy different position and display different reciprocal topographic relationships in different groups. That shows their mutual dissociability during their evolutionary (probably Permian) radiation. This was probably made possible by the plasticity of the interstitial (mainly mesenchymal) tissue, which displayed variability more readily, was more readily influenced by mutations and was capable of forming an induction cascade and network. Variability and mutation made it more satisfactory for selection at times when catastrophic environmental changes produced these in excess, acclerated evolution and changed bradytely to tachytely. In birds this was particularly accentuated, since they took over a new, hitherto vacant zone. This intensified tachytely is also to be seen in the morphogenesis of recent birds, since the structures mentioned are not recapitulated and they appear by way of archallaxis, whereas in Lacertilia the recapitulation method is largely applicable. Preadaptations also came into consideration for the evolution of such specialized structures. The genetic plasticity of the interstitial tissues, the possibility of achieving a big evolutionary effect from a small cause and the enormous length of geological time do not negate the possibility that evolution advanced by way of small variations and small point mutations, whose successful application in selection was made easier by dissociability, while in turn, point mutations, with the possibility of a quantity of progressive adequate selections, made the way easier for integration. The problem of complex development of the components of a specialized structure can thus be explained by Needham's (1960) theory of dissociability. The individual dissociated components, in mutual interaction in the enclosed, limited space are coordinated to such a degree that the final product is the resultant of their precise cooperation.