The biota represents the first known experiment in multicellularity, with no extant multicellular descendants. As multicellularity evolved many times, sterile somatic cells did too. Signal transduction mediated by the superfamily of GPCRs dates back to the origin of multicellularity. Complex multicellularity is different from "simple" multicellularity, such as colonies of organisms living together. King identified choanoflagellates as key organisms to answer questions about the origin of multicellularity. Possibly by around 900 Ma true multicellularity had also evolved in animals. King studies the evolution of multicellularity and choanoflagellates. Additionally, multicellularity appears to have evolved independently many times in the history of life. The Acrasidae slime molds are the only excavates to exhibit limited multicellularity. The most recent snowball episode may have triggered the evolution of multicellularity. Loss of multicellularity occurred in some groups. A subsequent major change was the advent of multicellularity. Cancer in animals (metazoans) has often been described as a loss of multicellularity. "Dictyostelium discoideum" is a widely used model for cooperation and the development of multicellularity. Multicellularity also permits increasing complexity by allowing differentiation of cell types within one organism.