HAP2/GCS1: Mounting evidence of our true biological EVE?

Sex has consequences—indeed, where would we be without it? Yet for all its importance, remarkably little is known about how sex evolved, why it has persisted, or even what mechanisms allow sperm–egg fusion to occur. Fortunately, answers to these questions are beginning to emerge with studies of hapless 2/generative cell specific1 (HAP2/GCS1), a molecular machine that promotes gamete fusion in organisms ranging from protists to flowering plants and insects. In studies by Fedry and colleagues, key structural features of the HAP2 protein are revealed for the first time, lending new insights into its mode of action and reinforcing its relationship to viral proteins that accomplish a similar task and may be intimately linked to the origins of cell–cell fusion events (including sexual reproduction) across evolutionary time.