Book review of Bonduriansky; R. & Day, T.2018. Extending heredity to better understand evolution, Princeton University Press, 288 pages, ISBN: 9780691157672, $29.95

According to the Oxford Dictionary, heredity is ‘the passing on of physical or mental characteristics genetically from one generation to another’ (https://oxforddictionaries.com). My biological dictionary agrees (Lawrence 2008). In this fascinating book, evolutionary biologists Russell Bonduriansky and Troy Day (B&D from here on) argue that we should abandon this genetic definition of heredity, and instead embrace a heredity concept that includes all the mechanisms by which parents influence the development of their offspring. Does this not sound immensely sensible? After all, parents do not just dump genomes on the ground and hope that something will happen—they always produce a highly organized egg, may sometimes build a nest, or interact behaviorally with their offspring to enable them to acquire the skills they need in life. Yet, evolutionary biology is built on transmission genetics, assuming that everything else that parents do to their offspring can be considered ‘fully encoded in the genome’ (p.12). B&D reveal that this gene-centric perspective on heredity was never particularly well grounded or supported, and they draw on the contemporary literature to show that extra-genetic inheritance is not just an empirical fact, but that it also is predicted theoretically to affect what happens in evolution. B&D’s perspective is a generalization of what is known as ‘dual-inheritance theory’, which is familiar from models of gene-culture co-evolution (Boyd and Richerson 1985). Genetic and extra-genetic inheritances are considered separate, but potentially interacting, channels that transmit ‘distinct types of information’ (p.18). While this is a sensible way to handle heredity, the rationale for the distinction is largely left to the reader’s intuition. In particular, one may wonder what it actually means to ‘transmit information’, and if all mechanisms by which parents influence their offspring also are ‘channels of transmission of information’ (Shea et al. 2011)? Be that as it may, B&D demonstrate the power of dual inheritance modeling by establishing that extra-genetic inheritance influences evolution in both the shortand long-term. Their starting point is the Price Equation, a general mathematical formulation of change in the average trait value within any population of entities (Gardner 2008). While this may sound bold for a book aimed at a general biology readership, the treatment is light-hearted, explanations are intuitive rather than technical, and there is ample use of simple graphics instead of formulas. The result is an excellent introduction to how and why extra-genetic inheritance influences phenotypic and genetic evolution. Here, as well as throughout the book, the extensive use of informative footnotes makes it easy for the curious reader to figure out where to go for more. One refreshing aspect of the book is the no-nonsense, down to earth, perspective on the relationship between science and society. B&D point out that, similarly to how politics fueled Lysenkoism in the Soviet Union, racist views in Western Europe and North America promoted the view that inheritance is synonymous with genetic transmission. Another extraordinary story is how the widely known effects of maternal alcoholism on fetal development were purged from the collective memory, because it did not fit the genetic view of heredity, and later had to be rediscovered. These are reminders that science is a social enterprise, and that there is scientific value in reflecting on the core concepts of our disciplines.