The sudden appearance of novelty is not, as Otto Schindewolf emphasized, an unusual aspect of the fossil record. - Jeffrey H. Schwartz

If Walter Garstang's suggestion is correct, and chordates did arise from a tunicate-like form by retaining the chordate features of their larval stage of development into adulthood, then the first chordates must have been affected by a regulatory mutation that kept the Manx gene activated for a longer period of time.

As was demonstrated as long ago as the 1930s by the German experimental geneticist Hans Grüneberg, neither structural reduction or loss, nor structural addition, is a completely gradual process. Instead, the loss or gain of a structure is developmentally constrained to be more step-wise, or saltational.

The observation of reduction in complexity in many groups or organisms after a structure has emerged in a full-blown state makes sense in terms of homeobox genes.