POSSIBLE CONTRIBUTIONS FOR THE DEVELOPMENT OF EXAPTIVE THEORY: THE EXAMPLE OF RACHIS

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M. Tanga *
G. Gelati
(*) Corresponding Author:
M. Tanga | m.tanga@tin.it

Abstract

Aiming at finding an objective method to define as exaptive (or as not exaptive) an evolutionary transformation, we can use a morphological and morphometric analysis of vertebras that can be realized through laser scanner technology. So we can reach a comparative valuation of rhachidian exaptive transformations from a typology of animals to another. In our work we referred to vertebras of a mammal tetrapod (chamois), of aquatic mammals (common fin whale, bottlenose dolphin) and of Man. We can suppose that the evolutionary transformation of the examined organ, system or structure is exaptive if: i) it remains the same under the phylogenetic/genetic profile, in other words it is the homologous; ii) it remains the same (exactly the same or however within certain limits that must be quantified by opportune indicators/descriptors) according to the morphometric/morphologic aspect; iii) its successive function changes with discontinuity if compared with the previous one; this aspects can be studied by modal analysis and by the model of Eigenvectors and Eigenvalues; iv) the new function is exclusive or however is prevailing on the original one. In particular, regarding rachis: i) we know the phylogenetic/genetic correspondence of this structure in all vertebrates; ii) we could choose some morphometric parameters as indicators of the maintaining/changing of structure; iii) we compare the previous and successive function under static/dynamic aspects. We refer to last year report, when we proposed that the evolutionary transformations of rachis static/dynamic function can be considered as exaptive. The functional transformation pushed us to rename human rachis as “vertebral shock absorber”, due to its new vertical set-up, very different from the horizontal one that is proper of central axis (fishes and, later, of Cetaceous, even if in a different way), of beam (of tetrapods) and of shelf (of “partial” bipeds).

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