 A recent microbiology topic of growing interest for philosophers is microbiome research, which examines all the microbial communities living in host organisms. In humans, the gut microbiome in particular is associated with many health and disease states experienced by the host, including mental health. There are two foci of philosophical attention given to these heterogeneous microbial consortia in host systems, namely individuality (e.g., Skillings 2016) and causality, specifically the causal role large mixed communities of microbes might play in host health (Lynch et al. 2019). 