 As we can see, there is no general answer to the question whether or not animal studies are valuable from a purely epistemic (as opposed to ethical, economic, or combined) view. Other authors have developed a practice-based taxonomy of animal modes to allow more accurate assessment of the epistemic merits and shortcomings, and predictive capacities of specific modeling practices (Degeling and Johnson 2013). There is much evidence that species differ enormously with respect to their susceptibility to have toxic reactions to substances. Thus, while it is very likely that for any one toxin, there is some species that is predictive of the human response, it is often hard to tell which one is most appropriate for any particular toxin. A species that predicts the human response well for one substance may be a bad model for another. However, some authors suggest that extrapolations  from animal models have been made successfully in at least some cases (Steel 2008 discusses the extrapolation of claims concerning the carcinogenicity of aflatoxin from Fisher rats to humans; see Reiss 2010a for a critical appraisal and Steel 2013 for a response).