Title: More Is Faster: Why Population Size Matters in Biological Search

Abstract: There are many instances in biology of multiple searchers attempting to find one or more targets, where a successful search results in a cascade of events. For example, a foraging ant colony consists of many individual ants searching a landscape for food; when one ant finds food, it may lay pheromones that communicate the location of that food resource to nestmates. Similarly, a population of immune cells searches for antigens in lymph nodes to initiate a cascade of replicating B or T cells. Once a large population of T cells specific to a particular pathogen is created, those cells travel to infected tissues and search for cells infected with that pathogen. In each of these cases, the time it takes for the initial discovery is of critical importance - the first ant that finds a seed and the first T cells that find cognate antigen or an infected cell. However, most models in biology only consider the typical or average case. In the cases described above, the first discovery changes the search process for all subsequent searchers, and so here, we focus on the first contact time that initiates other downstream events.