Are current critiques of the theropod origin of birds science? Rebuttal to Feduccia (2002)

Auk, The, Apr 2003 by Prum, Richard O

The molecular developmental data provide a transition series in the evolution of feathers and feather branched complexity that is based entirely on the molecular developmental experiments (Fig. 4) (Harris et al. 2002). Compellingly, these independent molecular data are exactly congruent with predictions of the developmental model of the evolution of feathers which was based on the classical feather development literature (Fig. 2) (Prum 1999). Our findings demonstrate that feathers are homologous with scales at the placode stage, but that the feather bud and all subsequent feather structures are evolutionary novelties that are not homologous with a scale or parts of a scale. Many of the molecular signaling systems involved in the initial development of scales and feathers are shared between the two structures because of the homology of their placodes. These plesiomorphic similarities permit the experimental manipulation of scale development, producing the "transformation" of scale placodes into feather placodes, as cited by Feduccia (2002). In no way, however, do those experiments support the general homology of parts of feathers and scales, as required by the hypothesis that feathers evolved from elongate scales.

The developmental model of the origin of feathers (Prum 1999) has now been supported by both paleontological (Prum and Brush 2002) and molecular data (Harris et al. 2002). The developmental theory of the origin of feathers, the new Shh-Bmp2 data of feather development (Harris et al. 2002), and the theropod hypothesis of the origin of birds provide the first coherent understanding of the origin and evolution of feathers.

CONCLUSION

In his commentary and previous publications, Feduccia has proposed a hypothesis of avian origins that is untestably vague, interpreted evidence inconsistently in favor of his hypothesis, rejected objective scientific methods of reconstructing evolutionary history, changed the standards of evidence when new data are produced, and assumed the existence of convergence that has yet to be demonstrated (i.e. begged the question). Now, having accepted the existence of feathered dromaeosaurs, Feduccia has contradicted decades of his own work by hypothesizing that dromaeosaurs are actually flightless birds in order to maintain the same conclusion-that birds are not theropod dinosaurs. Feduccia's rhetoric is beyond qualifying as the "most subjective and qualitative field of biology." My conclusion is that this is not science, but a rhethorical sham.

As Thomas Kuhn (1970:79) wrote in The Structure of Scientific Revolutions,

To reject one paradigm without simultaneously substituting another is to reject science itself. That act reflects not on the paradigm but on the man. Inevitably, he will be seen by his colleagues as "the carpenter that blames his tools."

By offering no testable alternative to the theropod origin of birds and maintaining that the origin of birds is potentially unsolvable, Feduccia and other critics of the theropod hypothesis of avian origins reject science itself. One-sided rejections of the theropod origin reflect not on the hypothesis, but on intellectual weaknesses of the critiques.