Biological systems can maintain memories over long timescales, with examples including memories in the brain and immune system. It is unknown how functional properties of memory systems, such as memory persistence, can be established by biological circuits. To address this question, we focus on transgenerational epigenetic inheritance in Caenorhabditis elegans. In response to a trigger, worms silence a target gene for multiple generations, resisting strong dilution due to growth and reproduction. Silencing may also be maintained indefinitely upon selection according to silencing levels. We show that these properties imply the fine-tuning of biochemical rates in which the silencing system is positioned near the transition to bistability. We demonstrate that this behavior is consistent with a generic mechanism based on competition for synthesis resources, which leads to self-organization around a critical state with broad silencing timescales. The theory makes distinct predictions and offers insights into the design principles of long-term memory systems.

生物系统可以长时间维持记忆，例如大脑和免疫系统中的记忆。目前尚不清楚记忆系统的功能特性（例如记忆持久性）如何通过生物电路建立。为了解决这个问题，我们重点关注秀丽隐杆线虫的跨代表观遗传。为了响应触发因素，蠕虫使目标基因沉默多代，抵抗生长和繁殖引起的强烈稀释。根据沉默水平的选择，沉默也可以无限期地维持。我们表明，这些特性意味着生化速率的微调，其中沉默系统位于接近双稳态的过渡处。我们证明这种行为与基于合成资源竞争的通用机制一致，这导致围绕具有广泛沉默时间尺度的临界状态的自组织。该理论做出了独特的预测，并为长期记忆系统的设计原理提供了见解。