 There remains disagreement on how to characterize the relevant notion of complexity, however. As Querbes, Vaesen, and Houkes (2014) note, increase in cultural complexity has been characterized in several ways, including as an increase in a trait’s fitness, as an increase in the number of elements that make up a trait, and as an increase in the difficulty of transmitting the trait faithfully (see also Mesoudi &amp; Thornton 2018) or how difficult it is to learn (J. Henrich 2004). These characterizations are not theoretically or empirically equivalent, and each suffers from its own shortcomings. Specifying complexity in terms of fitness, for instance, seems to require an agreed upon metric for cultural fitness, but no such metric has been widely accepted (Ramsey &amp; De Block 2017). Relatedly, while it is relatively easy to recognize episodes of technological change that are instances of progress, it is far less clear how to evaluate changes in other kinds of cultural traits, and so it remains difficult to know when transformations in, say, a religious or linguistic system should be classified as improvements or degradations (Miton &amp; Charbonneau 2018).