Newborns and hatchlings can perform incredibly sophisticated behaviors, but many animals abstain from sexual activity at the beginning of life. Hormonal changes have long been known to drive both physical and behavioral changes during adolescence, leading to the largely untested assumption that sexuality emerges from organizational changes to neuronal circuitry. We show that the transition to sexuality in male Drosophila is controlled by hormonal changes, but this regulation is functional rather than structural. In very young males, a broadly acting hormone directly inhibits the activity of three courtship-motivating circuit elements, ensuring the complete suppression of sexual motivation and behavior. Blocking or overriding these inhibitory mechanisms evokes immediate and robust sexual behavior from very young and otherwise asexual males. Similarities to mammalian adolescence suggest a general principle in which hormonal changes gate the transition to sexuality not by constructing new circuitry but by permitting activity in otherwise latent motivational circuit elements.

新生儿和刚孵化的幼体可以表现出极其复杂的行为，但许多动物在生命之初就避免性活动。长期以来，人们都知道荷尔蒙的变化会导致青春期期间身体和行为的变化，这导致了一种基本上未经检验的假设，即性是由神经元回路的组织变化产生的。我们发现，雄性果蝇向性行为的转变是由激素变化控制的，但这种调节是功能性的，而不是结构性的。在非常年轻的雄性中，一种广泛作用的激素直接抑制三个求偶激励回路元件的活动，确保完全抑制性动机和行为。阻止或超越这些抑制机制会引起非常年轻和其他无性男性的立即和强烈的性行为。与哺乳动物青春期的相似之处表明了一个普遍原则，即荷尔蒙变化不是通过构建新的回路而是通过允许其他潜在动机回路元件的活动来控制向性的转变。