Our bodies are rife with genes and the majority of them aren’t even ours. We all have a strong sense of our own individuality, but the truth is that our bodies are hotels for a diverse array of microbes including bacteria and fungi. The numbers are simultaneously creepy and humbling. Tot up all the cells in our bodies and the microbial ones would outnumber our own by a factor of ten. The five feet of our large intestine houses the majority of these microorganisms and contain up to 100 trillion of them.

These single-celled tenants are known as the microbiota and they carry their own sets of genes. Some of these are incredibly important to us because they allow