The symmetrical transverse stripes shown by many vertebrates are an evolutionary puzzle that may be explained under the proposed model. On the same common-sense grounds on which we should reject the gradual elaboration of segmented skeletons, let us reject the idea that the stripes of zebras (for example) have arisen gradually through through natural selection of the positioning of random blotches of coloration.
It is easier to believe that the striped pattern has an internal structural base, that there is a developmental relationship to a fundamental segmented skeletal structure. The idea is that each primitive segment or developmental somite produces one marking against a background color, that is, one pair of contrasting colors; chained together, a repetitive pattern is formed. Each stripe reflects a particular pair of growths (of distinct zones of melanocyte activity and inactivity) which may be traced to a particular somite or fundamental segment, which may or may not have ever developed to a point where it was visible as a somite or visible as any type of skeletal segment.
Fig.5 Zebra and protovertebrate
The bony skeletons of vertebrates are the least distorted aspect of anatomy, in relation to the symmetrical segmented form of the proposed progenitor. The musculature and the circulatory and nervous systems still show vestiges of the primitive segmented condition, particularly in the embryo, but the pattern is less evident. Evolutionary distortion, fusion, and loss have been more drastic among the soft parts. But the stripes of the zebra are an exception, showing a symmetrical pattern which may be explained as reflecting the form of a primordial vertebrate ancestor. The head and limb markings are particularly suggestive. The swept-forward radials that fuse to form the skull seem apparent in the head markings. The transverse stripes around the limbs suggest homology with the axial skeleton, which also has transverse stripes.
Many animals have fewer markings than zebras, in less symmetrical patterns; these may be seen as reductions and distortions of the original pattern. Note that where stripes on the trunk are parallel to the spine, they are few in number and relatively amorphous. Also note that while there is much individual variation among the stripes of, for example, a zebra, all seem to vary from--or approximate to--one basic pattern.
The above theory concerning the development of stripes is taken from an article by Mintz(1967), and comments by Ede(1978). I do not claim that either would support my evolutionary model, or my reading of their work.
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