An untestable theory is one that is not verifiable by sense perception and its extensions. This is never the case with theories about organic evolution; these are claims about the physical world. Such claims are scientific, not metaphysical, no matter how remote the possibility of empirical verification may seem.
The radical theory advanced above may be maintained on the basis of the existing evidence; competing theories of vertebrate and arthropod origins enjoy no stronger support. Since the proposed model is unusual, it is possible that evidence which would support it does exist but has been disregarded as insignificantly anomalous. Such evidence might include early fossils showing extensive serial homology. Extensive serial homology is obvious in many early Paleozoic fossils; this suggests that segmentation formed rapidly.
There are possibilities for experimental corroboration of the proposed model. Generally, there is potential value in any experimental procedure which tends to restore a primitive level of differentiation not present in the modern organism. Perhaps most intriguing are experiments in which a grafted part is affected by host tissues such that it attains a degree of differentiation which it does not attain normally, as when a tail grafted onto a limb bud differentiates into a limb with digits. Such phenomena are explicable under the proposed model, but there is no explaining the sudden appearance of new complex symmetrical segments in functional positions through random variation alone. There is no way to explain why new segments don't appear at random throughout the body, except by conceiving mutations to be variations in the expression of an existing fundamental structural complex.
The theory would be falsified by the discovery of fossil series of probable direct descent showing gradual evolutionary elaboration in the number of skeletal parts or in the symmetry between parts, that is, evidence contravening the principle of reduction and specialization of serial homologs. The proposed theory would be weakened by the empirical or theoretical discovery of a mechanism through which such gradual increase in number of segments could occur.
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