Doctoral student Amar Sarkar and colleagues describe this concept as the social microbiome. “Some keys to human evolution are encoded outside the human genome,” said Sarkar’s adviser, associate professor of human evolutionary biology Rachel Carmody. The social microbiome is the collective sum of the microbiomes within an interacting group of organisms: family, classmates, or friends. Sarkar, Carmody, and teaching fellow Cameron McInroy define the social microbiome as the collective sum of the microbiomes within an interacting group of organisms: family members, classmates, or a circle of friends. “So, when obese and lean mice are then co-housed, the obese mice actually lose weight, in part by taking on some of these lean microbes,” explained McInroy.