Variational tendencies are the dispositions of biological systems to generate evolutionarily relevant variation. Modularity, robustness, plasticity and evolvability are chief among them. Evolutionary developmental biology, or evo-devo, considers these properties as intrinsic dispositions of traits as differentiated units of development and evolution. In this paper, we address the characterization of these variational tendencies attributed to traits in evo-devo. After arguing that current theories in evo-devo cannot properly explain why traits do, in fact, vary, we propose to characterize them as natural dispositional kinds. In doing so, we appeal to metaphysical resources regarding the characterization of dispositions. From this metaphysical framework, it is possible to argue that only by attributing dispositions to traits (conceived of as natural kinds), it is possible to make sense of their causal and explanatory power. We argue that this particular case study constitutes an example of a kind of interaction between metaphysics and biology that we label Metaphysics from Biology, where the specific demands of a complex reality such as evolution require the development of metaphysical notions that seem to go beyond those given in the literature.