 That the scientists largely agree about the practice of statistical estimation shows that they largely share some tacit concepts of selection and fitness, ones it would be an advance for philosophers to define. Philosophers have developed definitions of fitness. Brandon was the first to defend the propensity interpretation of fitness and it has earned much discussion since (Brandon 1978; Mills &amp; Beatty 1979; Rosenberg 1982; Brandon &amp; Beatty 1984; Brandon 1990; Sober 2000). Rosenberg and Bouchard have developed a recent definition of fitness based on the relationships between an individual and its environment that contribute to the individual’s success (Bouchard &amp; Rosenberg 2004; for more on “fitness” see entry on  fitness).