 Godfrey-Smith (2009: 83; see also Okasha 2006: 14) takes issue with Griesemer’s requirement of “material overlap” as being too narrow a definiendum of reproducers. He thinks that reproducers need not contribute actual material to their progeny (where they template for sequences, as in the case of viruses). Griesemer believes Godfrey-Smith has over-interpreted the requirement; he is primarily concerned with the idea that parents cause progeny (Griesemer 2014). Charbonneau (2014) furthers the move made by Godfrey-Smith, arguing that the existence of parent-offspring lineages is unnecessary for evolution by natural selection to occur.