Sexual differentiation of brain and behavior is largely a hormonally driven process occurring perinatally in rodents and prenatally in primates. Considered early life programming, this process occurs at a time when the brain is remarkably immature and often does not manifest until reproductive maturity, raising the question of how brief hormonal exposure early in life could have such an enduring effect. Epigenetic modifications that occur early and persist into adulthood is one feasible explanation. Sufficient evidence exists to confirm that there are indeed epigenetic changes to specific brain regions induced by steroid hormones in males to differentiate them from females, but whether they persist into adulthood is unclear. Regardless, there are strong correlations between early epigenetic changes and adult brain and behavior. Moreover, although generally referred to as a permanent process, there is evidence that adult sex-typic behaviors are malleable and even reversible in mammals under certain conditions and these may be a function of epigenetic maintenance of gene expression that impacts behavior.

大脑和行为的性别分化在很大程度上是由激素驱动的过程，发生在啮齿动物的围产期和灵长类的产前。考虑到生命早期编程，这个过程发生在大脑明显不成熟的时候，并且通常直到生殖成熟才出现，这引发了一个问题，即生命早期短暂的激素暴露会产生如此持久的作用。早期发生并持续到成年的表观遗传修饰是一种可行的解释。有足够的证据证实雄性类固醇激素确实会引起特定大脑区域的表观遗传变化，以使它们与雌性区分开，但尚不清楚它们是否能持续到成年。无论如何，早期表观遗传变化与成年大脑和行为之间有很强的相关性。此外，