The fact that cells produce signaling molecules that are readily recognized by other cells is understandable. What’s more mysterious is why almost all cells in nature, from one-celled organisms to cells in humans, are also capable of detecting their own chemical signals. Hyun Youk and Wendell A. Lim of the University of California, San Francisco, have now shown that this “secrete and sense” property is crucial for a host of complex social and asocial behaviors that affect cell dynamics in many biological contexts (Science 2014, DOI: 10.1126/science.1242782). The researchers engineered yeast cells to secrete and sense a mating pheromone. The cells fluoresce green in response to the pheromone. The researchers also prepared a sense-only yeast that doesn’t produce its own pheromone but fluoresces red in response to a foreign pheromone. In this system, differences in the levels of green and red fluorescence indicate the amount of self-sensing the first group is doing. Youk and Lim found they could tune the complex relationships between cells sensing themselves and cells communicating with their neighbors by adjusting the density of cells and other factors. “The ability to tune self-communication versus neighbor communication in multicellular microbial systems … may provide a way to better understand the advantages of cooperative versus self-driven behaviors,” the researchers write.