Great post Kevin. A related area to Robustness, especially in the context of Complex Adaptive Systems, is found in the concept of Degeneracy: circumstances where structurally dissimilar components/modules/pathways can perform similar functions (i.e. are effectively interchangeable) under certain conditions, but perform distinct functions in other conditions. See: (1) Whitacre, J.M. and A. Bender, Degeneracy: a design principle for achieving robustness and evolvability. Journal of Theoretical Biology, 2010. 263(1): p. 143-53. (2) Mason, P.H., Degeneracy at Multiple Levels of Complexity. Biological Theory, 2010. 5(3): p. 277-288.

Human culture shields us from the rigours of natural selection. Hmm, no, that's not technically true. Culture isn't some homogeneous entity; instead, different cultural features will interact with biology in different ways. Just look at the literature on gene-culture coevolution! One paper I particularly recommend is by Laland, Odling-Smee & Myles (2010): How culture shaped the human genome: Bringing genetics and the human sciences together.

Different environment does not mean different selection. It can mean weaker selection, and consequent accumulation of deleterious mutations Why are you addressing that comment to me? I didn't say anything along those lines. All I said was that culture can interact with biology in different ways. One of these ways, as you note, might be a relaxation of the selection pressures, allowing for the accumulation of deleterious alleles. What I took umbrage with originally, and which Kevin has since clarified, was the idea of culture being some homogeneous entity that always shielded us from selection.

@ L: There are plenty of problems with the study, which is why I said in the post not to take the results too seriously. I agree that some of the population size estimates are going to be off in Ethnologue (just look at the citation date for their source). As a rule, I did try and double check the data with other sources, which is why it's taken me months to complete. In some cases this was simply not possible, so I just had to use the outdated, and potentially unreliable, information. On the area calculations -- I tried to get the most reliable data possible. This sometimes meant that I had to try and find other sources (e.g. government surveys). Failing that, I simply had to delete the language from the dataset. As I said above, Global Mapping International would be one alternative, if I were to do a proper study. On your second point: I did try and account for dialects, but obviously this is going to be far from perfect. In instances where the UPSID language turned up multiple dialect results on Ethnologue, I would try and do as much research as possible on said language to determine the exact demographic information. Again, sometimes this was not possible. Lastly, I acknowledge that you really need to take a leap of faith on accepting that the UPSID database is correct, and each language's phoneme inventory size is accurate. I can't really see any realistic way around this. There are plenty of other problems I can pick out: for instance, the language statistics may have been skewed by sudden changes in a population's demography, through recent events such as displacement and genocide. Ultimately, I think any study into this would have to build up a large body of mutually supporting evidence (through models and experiments) on top of a more rigorous study of the data. Really, my main motivation for this was to get a rough idea for myself, to see if it was worth pursuing for a future project. Thanks for your comment. Any other points on where I could improve my methodology would be appreciated, as I'm sure there are many things I've overlooked, and I need criticism such as this if I'm going to try and perform a proper scientific study in the future.