Darwin’s empirical claim and the janiform character of fitness proxies

Darwin’s claim about natural selection is reconstructed as an empirical claim about the causal relevance of the match between the individual and its environment for the condition of the individual, and the consequence of this condition for leaving progeny. It is shown that many fitness proxies are mediating between these two steps. They are indicators of the match and predictors of reproductive success at once. Modern concepts of fitness, in contrast, are focusing exclusively on the latter. Assuming that Darwin wanted to explain selection in terms of a modern concept of fitness thus confounds his argument. Taking the janiform character of fitness proxies serious, in contrast, does not only allow for integrating Darwin’s argument into current evolutionary biology, but also helps reframing and alleviating the dispute between the Modern Synthesis and the Extended Evolutionary Synthesis.