Rethinking heredity, again.

The refutation of 'soft' inheritance and establishment of Mendelian genetics as the exclusive model of heredity is widely portrayed as an iconic success story of scientific progress. Yet, we are witnessing a re-emergence of debate on the role of soft inheritance in heredity and evolution. I argue that this reversal reflects not only the weight of new evidence but also an important conceptual change. I show that the concept of soft inheritance rejected by 20th-century genetics differs fundamentally from the current concept of 'nongenetic inheritance'. Moreover, whereas it has long been assumed that heredity is mediated by a single, universal mechanism, a pluralistic model of heredity is now emerging, based on a recognition of multiple, parallel mechanisms of inheritance.