Across levels and timescales: causally linking genes, language processing and cultural evolution

Despite breathtaking recent progress, causal inference remains a very complex issue which becomes even more complex when studying phenomena that bridge multiple scales, levels and disciplines. This talk will focus on such a case, trying to link the population genetic structure to patterns of linguistic diversity. In a nutshell, this proposal suggests that structural properties of language might be influenced by the genetics of the speakers. Such influence must be very weak and indirect. Weak because we know that healthy children will acquire natively any language they happen to be raised into no matter their genetic makeup. Indirect because genes do not by themselves do anything to language and speech, not to mention group-level and historical phenomena such as language. Studying such cases rises a number of important questions including: What sort of data, methods, criteria and discourse must we use to support such long inferential chains crossing so many levels (molecular to social), timescales (milliseconds to generations) and disciplinary boundaries (molecular genetics to historical linguistics)? When and how do we decide that we have a causal explanation given the differences between disciplines (experimentation is not always possible)? How do we deal with loops in the process? How do we identify suppressors (for instance, compensatory strategies in speech articulation) and how do we control for them? In this talk I will use some more-or-less fictional examples to illustrate these difficulties but also to suggest approaches that might make such cases tractable, suggesting ways forward that should apply more generally to phenomena that bring the cultural and non-cultural together.