 The proximate-ultimate distinction can be given an epistemic or ontological reading. First, authors have interpreted it as distinguishing different kinds of explanations (Amundson 2005; Calcott 2013; Scholl &amp; Pigliucci 2015). This epistemic reading includes that how questions cannot be addressed by explanations citing ultimate causes (i.e., telling a story of adaptation) and that why questions cannot be addressed by explanations citing proximate causes (i.e., telling a story of trait development). Second, authors have interpreted this distinction as one between different ontological classes of causes working in ontogenetic and phylogenetic processes (Laland et al. 2013a). This ontological reading is backed up theoretically by Weismann’s concept of the separation of germ line and soma, which provides a demarcation line between two distinct classes of causes. To this day, biologists and philosophers have not reached a consensus on how exactly the division ‘proximate-ultimate’ or ‘how-why’ should be understood, epistemically or ontologically (Francis 1990; Dewsbury 1992, 1999; Sterelny 1992; Beatty 1994; Ariew 2003). Despite this lack of agreement this framework has been applied in various fields, from evolutionary biology (E. O. Wilson 1975 [2000: 23]), evolutionary psychology (Daly &amp; Wilson 1978; Crawford 1998) and behavioral ecology (Morse 1980: 92–95) to human sciences, like in human cooperation (Marchionni &amp; Vromen 2009) and developmental psychology (Lickliter &amp; Berry 1990). Especially in evolutionary biology it has contributed to mainstream causal reasoning for a long time, even among evolutionary biologists interested in developmental processes (see, e.g., Maynard Smith 1982: 6).