I critically assess two widely cited evolutionary biological arguments for two versions of the ‘Extended Mind Thesis’ (EMT): namely, an argument appealing to Dawkins’s ‘Extended Phenotype Thesis’ (EPT) and an argument appealing to ‘Developmental Systems Theory’ (DST). Specifically, I argue that, firstly, appealing to the EPT is not useful for supporting the EMT (in either version), as it is structured and motivated too differently from the latter to be able to corroborate or elucidate it. Secondly, I extend and defend Rupert’s (...) argument that DST also fails to support or elucidate the EMT (in either version) by showing that the considerations in favour of the former theory have no bearing on the truth of the latter. I conclude by noting that the relevance of this discussion goes beyond the debate surrounding the EMT, as it brings out some of the difficulties of introducing evolutionary biological considerations into debates in psychology and philosophy more generally. (shrink)