My aIm In this thesis is to analyse the 'evolutionary analogy', a particular form. of evolutionary epistemology which claims that scientific change is governed by the same mechanisms, or by mechanisms analogous to those at work in organic evolution, mainly natural selection. In tenns of research questions, the overall aim of this thesis is to answer 'Is the process of scientific change analogous to or even the same as organic change?' Many philosophers proposed evolutionary theories of scientific change - evolutionary analogies. By drawing analogies or even equating the mechanisms of organic and scientific evolution they described the process underlying the latter but also justified its value, implicitly or explicitly, by a simple analogy: better theories are those which survive old ones, as better species are those which survive previous ones. The results of these philosophers, however, have not been satisfactory and a novel approach is needed. In this thesis I am interested in a purely descriptive philosophy of science and my position will be based on the critique of the most recent and comprehensive attempt to defend the evolutionary analogy, made by David Hull. In order to answer the research question I have formulated above, the following issues will be addressed: what is organic evolution;. what is meant by 'evolutionary analogy'; how analogy/identity can be evaluated; how evolutionary analogy/identity has been defended by philosophers; how these defences perform; what is the best defence available; whether it passes the evaluation and, if not, whether it can be improved; if all the positions fail, whether it is possible to conceive alternative analogies between other relevant processes which do not incur the same problems. By addressing these issues, I will be able to conclude that the process of scientific change is different from organic change and that only loose analogies can be defended.