 While this reasoning strategy seems plausible, it may not be so pertinent for extrapolating from model organisms. Steel’s reasoning strategy pertains to cases where we want to infer from one system where we know a certain mechanism operates to a different kind of system about we do not (yet) know that the same mechanism operates. However, in biology there is often evidence to the effect that, in fact, very similar mechanisms operate in the model as well as in the target system. A particularly important kind of evidence is the existence of so-called sequence homologies between different organisms. These are usually DNA sequences that show a more or less strong similarity, in some cases even identity. As it is (like in the case of the genetic code discussed above) not likely that this sequence similarity is due to chance, it is normally attributed to common ancestry (hence the term sequence “homology”; in biology, this term in its modern usage indicates relations of shared ancestry). Sequence homology has proven to be a reliable indicator of similarity of mechanisms. To give an example, a highly conserved sequence element called the “homeobox”, which was first described in Drosophila, is today believed to play a similar role in development in an extremely broad range of organisms (Gehring 1998). When there are reasons to think that the model and the target share similar causal mechanisms due to common descent, the extrapolator’s circle does not arise.