 Cultural units do not form lineages: A closely-related criticism of memetics draws on the fact that while in genetic replication we can trace a new copy of a gene back to a single parent, ideas are rarely copied from a single source in a way that allows us to trace clear lineages (Boyd and Richerson 2000). Memeticists are fond of analysing religious belief in terms of the spread of memes. But while religious beliefs may well spread through populations of humans, it seems unlikely that we will always be able to trace token instances of faith back to one source. Instead, individuals often acquire belief in God through exposure to several believers in their local community. In these circumstances, belief in God is not caused by one identifiable earlier token of the same type. Within the realm of biological evolution, an understanding of Mendel’s laws has been important in explaining some aspects of evolutionary dynamics. Mendel’s laws rely on an understanding of genes as discrete, transmitted units. But if token ideas can appear in an individual in virtue of that individual’s exposure to several sources, then this makes it unlikely that anything close to Mendel’s laws will be discovered within cultural evolution. This suggests a practical limitation on enquiry that may result from this difference between ideas and genes. Criticisms of this form have been put especially forcefully by William Wimsatt (1999), who argues that the creative and inferential abilities of human users make it the case that any given idea, or item of technology, can have fluctuating numbers of cultural parents over time. This is because the causal sources of its reproduction may vary. Belief in God may sometimes be caused by exposure to a single charismatic evangelist, it may sometimes be caused by the joint inculcation of two biological parents, and it may sometimes be caused by immersion in a diffuse community of theists. Ideas and items of technology also have no stable analogue to the genome, or germline, because different elements within cycles of technological reproduction, including ideas, behaviours of artisans, and material elements of technologies themselves, can all temporarily acquire the status of replicators depending on the attention that human agents happen to be paying to them. Accidental variations in one’s mental plan for constructing a pot, or in one’s actions in producing the pot, or in the made pot itself, can all conceivably be reproduced when another artisan comes to make a resembling item. Wimsatt uses these disanalogies to highlight the formidable problems facing any effort to use population genetic models in the explanation of cultural change.