The concepts of hierarchical organization, genetic determinism and biological specificity have played a crucial role in biology as a modern experimental science since its beginnings in the nineteenth century. The idea of genetic information and genetic determination was at the basis of molecular biology that developed in the 1940s with macromolecules, viruses and prokaryotes as major objects of research often labelled “reductionist”. However, the concepts have been marginalized or rejected in some of the research that in the late 1960s began (...) to focus additionally on the molecularization of complex biological structures and functions using systems approaches. This paper challenges the view that ‘molecular reductionism’ has been successfully replaced by holism and a focus on the collective behaviour of cellular entities. It argues instead that there are more fertile replacements for molecular ‘reductionism’, in which genomics, embryology, biochemistry, and computer science intertwine and result in research that is as exact and causally predictive as earlier molecular biology. (shrink)