Can functionality in evolving networks be explained reductively?

Philosophers of biology disagree about an adequate explication of the concept of function. Instead of perpetuating the debate on the level of in principle-arguments, this paper aims first at reconstructing functional talk in the biological research papers of Marom and Braun, which focus on two different kinds of evolving networks, and in discussing the ontological consequences which the authors draw from their results. Marom investigates evolving neural networks controlling Braitenberg vehicles. Braun observes the evolutionary rearrangement or "rewiring" of the genetic network of genetically modified yeast on a short time scale. In both cases, the parameters under investigation are defined in functional terms. However, both authors report striking differences in the structures that realize one and the same function, as well as striking differences in the function of identical structures. From this, they construct an argument against reductionism. The second aim of my paper is an inquiry into the epistemic legitimacy of this conclusion. This requires addressing critically several concepts on which Marom and Braun's argument is built.