assumptions) of a hypothesis about how some natural phenomenon operates. Thus, they are held as strong affirmative evidence supporting a scientific theory. For instance, advocates of Intelligent Design (ID) theory made icons of the bacterial flagellum and a mousetrap by using them as definitive examples of the key concept of irreducible complexity (Behe 1996). Critics of intelligent design, therefore, strove to invalidate central tenets of design theory by discrediting such models as valid evidence for ID (Miller 2004; Clements 2009). NDT explains the origin of traits specific to the blind cavefish as a series of gradually accumulating adaptations derived from features of their ancestral surface fish relatives. Those adaptations are postulated as the products of random unguided genetic mutations. Purposeless adaptive variability was incorporated as a foundational assumption of neo-Darwinian theory, which is also known as the Modern Synthesis (MS). The NDT, with its subsequent interpretations of observable changes in blind cavefish, is heavily dependent upon several bedrock assumptions that are best articulated by evolutionary researchers themselves. “The random occurrence of mutations with respect to their consequences is an axiom upon which much of biology and evolutionary theory rests [Futuyma 1986]. This simple proposition has had profound effects on models of evolution developed since the modern Figure 1. Comparative morphology of Mexican tetra (A. mexicanus) surface fish and cavefish. A. Surface fish in left-lateral view, showing a common pattern of melanin pigmentation along dorsal sides of head, back and posterior regions (white arrows), posterior to the gill chamber (yellow arrow), and along the lateral line, with high concentrations toward the posterior end at the junction of the lateral line and tail (dashed white arrow). Xanthophores produce bands of yellowish pigment extending along the lateral line and into rays of the caudal fin. The eye is functional, with a pigmented iris surrounding the lens. B. Cavefish in left-lateral view with much lower numbers and spatial expression of melanophores in all regions where melanin is produced in the surface fish. The eye is absent due to apoptotic degeneration and removal of the primary components of eye anatomy during larval development and juvenile growth stages. Macrophotographic images by Scott Arledge and Michael J. Boyle. synthesis, shaping how biologists have thought about and studied genetic diversity over the past century” (Monroe 2022). “The core tenet of the MS is that adaptive evolution is due to natural selection acting on heritable variability that originates through accidental changes in genetic material. Such mutations are random in the sense that they arise without reference to their advantages or disadvantages…” (Charlesworth 2017). “A classical or Darwinian evolutionary system embodies a basic principle: purposeless genetic variation of reproductive individuals, united by common descent, coupled with…natural selection of those rare individuals that fortuitously express the traits that complement or thwart the contemporary selective pressures…it’s a process replete with chance” (Greaves and Maley 2012). Stephen J. Gould (2002) summarizes three criteria for genetic variability within neo-Darwinian theory by stating, “Variation, in short, must be copious, small in extent, and undirected. A full taxonomy of non-Darwinian evolutionary theories may be elaborated by their denial of one or more of these central assumptions.” Gould adds that the most important criterion is undirected variation. He emphasized that wholly unbiased variation is fundamental to evolutionary theory, going on to say “in a sense, the specter of directed variability threatens Darwinism even more seriously than any putative failure of the other two postulates [copious, small in extent]” and he clarifies the meaning of directed variation as “…adaptive pressures [that] automatically trigger heritable variation in favored directions…” Automatic triggers of specific responses would have much in common with the components and outcomes corresponding to human-engineered systems, and thus, “Darwin clearly understood the threat of directed variability to his cardinal postulate of creativity for natural selection” (Gould 2002). Precisely because cavefish are believed to validate the vital interpretive assumptions of Darwin’s selectionist theory of evolutionary adaptation (Table 1), and specifically because these core assumptions should be reexamined, but are rarely questioned, we took on the study of cavefish to separate fact from myth for this notably persuasive icon. B. Historical non-evolutionary interpretation for the origin of blind cavefish Interpretive assumptions are also integral to historical non-evolutionary interpretations for the origin of blind cavefish. Accordingly, we recognize that it is time to reassess these assumptions in light of our findings, and over two decades of molecular and genetic data compiled by a growing cavefish research community. A comparison of our findings with historical non-evolutionary and evolutionary assumptions is presented in Table 1. Because widely-popular explanations are an important focus of our research, we located an accurate representative example that clearly delineates interpretive assumptions of the historical approach. A prime illustration of a historical non-evolutionary response to Darwinian evolution is currently displayed in The Creation and Earth History Museum in Santee, CA., the original site of ICR’s Creation Museum. Their interpretation for the origin of blind cavefish is as follows: As genetic information is copied and passed on generation after generation, occasionally there are copying ‘mistakes’ known as mutations. Mutations have been observed to destroy, damage, or corrupt genetic information or to be neutral, but have never been observed to add new information. This is true even of so-called ‘beneficial’ mutations that may be advantageous to the surviving organism in some BOYLE, ARLEDGE, THOMAS, TOMKINS, AND GULIUZZA Testing the cavefish model 2023 ICC 121
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