Cultural evolution has been proposed as the mechanism by which human languages’ distinct features emerge. One of such features is structure, which is regarded as an optimal solution to the competing pressures for simplicity and expressivity in language learning and use. A recent experimental iterated learning study (Kirby et al., 2015) shows that structure can emerge from an unstructured language under these competing pressures, by implementing both a learning and a communication task in a transmission chain setup. However, as most iterated learning experiments, it was run on a written modality, which might be problematic if the aim is to drive conclusions about language in general—writing is not language’s default modality and was not present in early stages of language evolution. The present study carried out a partial replication of the aforementioned experiment, contrasting a written condition (analogous to the original) with a spoken condition, in order to test for possible modality effects. Results for the written condition did not replicate those in Kirby et al. (2015) in any of the measures, suggesting that motivational factors could have played a crucial role in the previous findings. This hinders the interpretations of modality effects and suggests the need of further work.Cultural evolution has been proposed as the mechanism by which human languages’ distinct features emerge. One of such features is structure, which is regarded as an optimal solution to the competing pressures for simplicity and expressivity in language learning and use. A recent experimental iterated learning study (Kirby et al., 2015) shows that structure can emerge from an unstructured language under these competing pressures, by implementing both a learning and a communication task in a transmission chain setup. However, as most iterated learning experiments, it was run on a written modality, which might be problematic if the aim is to drive conclusions about language in general—writing is not language’s default modality and was not present in early stages of language evolution. The present study carried out a partial replication of the aforementioned experiment, contrasting a written condition (analogous to the original) with a spoken condition, in order to test for possible modality effects. Results for the written condition did not replicate those in Kirby et al. (2015) in any of the measures, suggesting that motivational factors could have played a crucial role in the previous findings. This hinders the interpretations of modality effects and suggests the need of further work.