A major limitation of asynchronous graphic communication is that misunderstandings can never be repaired in real time (REF Topics paper). Thus, it could be the case that specific coordination demands of successful asynchronous communication already exert too much inertia on the system. We know from other historical contexts that apparently non-optimal writing systems still manage to be transmitted with high fidelity. Eg, writing systems that have enormous redundancy and graphic complexity (eg, xxx) or those that are borrowed from elsewhere and whose typologies are ill-suited to the phonology of the new language. 
All experimental participants will already be literate in the Roman script and perhaps others. This means that the experiments and the historical data are not directly comparable on the dimension of literacy. Consequently, changes to the Vai input across experimental generations may be conditioned by prior literacy in another linear script, thus items may become more Romanised over time. In itself, this does not undermine the premise since our study is interested in detecting compression regardless how that compression is actualised. 

Concluding remarks and impressions

If Vai is shown to evolve towards a compressible system we may speculate as to how informative this may be for understanding the early evolution of writing. Early Vai certainly shares characteristics of the four origination events we have mentioned earlier: widespread logography with iconicity, variable orientation, seria continua etc.
Graphemes will become more similar to one another. In other words, these items will come to be be generated from the same set of rules, resulting in typographic stereotypes (as for example, ‘stems’ in the Roman script ‘bowls’ and ‘lunettes’ in the Arabic script etc). Within character shapes, any repetitious forms will become abbreviated. In other words, standard repetitions will come to be inferred.

Acknowledgments

The following institutions and individuals helped us secure rare manuscripts for our dataset: Asien-Afrika-Institut (University of Hamburg), Hella Bruns (Max Planck Institute for the Science of Human History, Jena), Valerie Haeder (Library of Congress, Washington). We consulted the Indiana University Liberian Collections, but no dateable and digitised Vai manuscripts were available. The primary Vai data was tabulated by Olena Tykhostup (Freidrich Schiller University, Jena). Thomas Müller (The Mint, MPI SHH) compiled the German words and sentences for the Bilerian experiment.