Unjustified assumptions of inheritance

An important difference between biological and cultural evolution is that biological inheritance is transmitted from parent to offspring (vertical transfer) whereas cultural information can be transmitted between any two individuals (horizontal and vertical transfer), and consequently between any two populations. The amount of horizontal transfer has been shown to be of importance for the reliability of results of phylogenetic methods in anthropology (3, 4, 5, 6). There is even evidence of horizontal transmission of language elements (7), rendering a reconstruction of the history of a single language element unreliable even on its own phylogeny.These issues are currently of intense interest , something that Currie et al. acknowledge but do not handle. No phylogeny for political organization has yet been found, but one may nevertheless exist. However, it is also possible that political organization has spread mainly by diffusion. Currie et al. discuss this and point out that their own simulation studies have shown that phylogenetic methods are robust in relation to realistic transmission scenarios (8) , without defining realistic. Neither do they clarify why their own simulations on continuous data provides contrary evidence to simulations on categorical data (10, 11) (political organization is categorical). Further, political organization is a single trait that may or may not be in agreement with any statistical pattern.The authors claim that political organization has a number of characteristics that makes diffusion unlikely. These combine to make political organization too complicated to diffuse. This assertion is untestable and not a sound scientific motivation for not empirically testing the possibility of horizontal transfers, e.g. with a test for phylogenetic signal (12, 13).There are many examples of diffusion of complex cultural traits. A relevant case concerns the spread of democracy. Democracy was virtually unimplemented in the 18th century. From this humble beginning it has spread and is today one of the most common forms of governance (14). Rather than having been inherited democracy has spread by diffusion. Observing behaviours of others and adopting successful traits, or adopting traits of successful individuals or societies, is common (15). To assume different rules for the spread of political complexity in Austronesia than those that have proven valid in the developed world is to assume that people who live in cultures other than our own use different criteria when evaluating cultural traits. This has not yet been shown.The unknown status of why any given cultural trait is present in any given ethnic group is a well-known problem in anthropology, having its own term: Galtons problem (16). One has to control for both horizontal transfer and common descent in order to make inferences about the presence of cultural traits. Phylogenetic methods have been imported from biology to correct for problems caused by common descent. Now, it seems, the problem of horizontal transfer is forgotten instead. This renders the results of Currie et al. unreliable.