Dr Pierrick Bourrat's new book is available for a short time for free online. Here is how Pierrick describes his Facts, Conventions, and the Levels of Selection:

"This book is the culmination of many years of thinking about levels of selection. It develops the idea that conventionalism about units and levels of selection cannot be regarded as benign if units and levels of selection are real and of biological significance. Similarly, practice cannot be the sole guide to pick out the relevant units and levels of selection.

Getting clear about the distinction between “genuine” units of selection which can serve as the basis to define a level of selection from arbitrary ones has important ramifications for biologists and philosophers aiming to explain evolutionary transitions in individuality (a subset of major transitions in evolution), such as the emergence of multicellular organisms from unicells.

I propose a set of criteria, inspired by the notion of “non-aggregativity” proposed by Bill Wimsatt, that permit one to make such a distinction. I show some of the ways in which these criteria could be deployed in a practical context and how they can be implemented in the Price equation and quantitative genetics."