The linear no-threshold (LNT) risk model is the current human health risk assessment paradigm. This model states that adverse stochastic biological responses to high levels of a stressor can be used to estimate the response to low or moderate levels of that stressor. In recent years the validity of the LNT risk model has increasingly been questioned because of the recurring observation that an organism's response to high stressor doses differs from that to low doses. This raises important questions about the biological and evolutionary validity of the LNT model. In this review we reiterate that the LNT model as applied to stochastic biological effects of low and moderate stressor levels has less biological validity than threshold or, particularly, hormetic models. In so doing, we rely heavily on literature from disciplines like ecophysiology or evolutionary ecology showing how exposure to moderate amounts of stress can have severe impacts on phenotype and organism reproductive fitness. We present a mathematical model that illustrates and explores the hypothetical conditions that make a particular kind of hormesis (conditioning hormesis) ecologically and evolutionarily plausible.

线性无阈值（LNT）风险模型是当前的人类健康风险评估范例。该模型指出，对应激水平高的不良随机生物学反应可用于估计对应激水平低或中度的反应。近年来，LNT风险模型的有效性受到越来越多的质疑，原因是不断观察到生物体对高应激源剂量的反应不同于对低剂量应激物的反应。这就提出了有关LNT模型的生物学和进化有效性的重要问题。在这篇综述中，我们重申，LNT模型应用于低和中度应激源水平的随机生物学效应，其生物学有效性低于阈值模型，尤其是钟表模型。这样，我们在很大程度上依赖于诸如生态生理学或进化生态学等学科的文献，这些文献显示了暴露于适度压力下如何对表型和有机体生殖适应度产生严重影响。我们提供了一个数学模型，该数学模型说明和探索了使一种特殊的增效剂（调节性增效剂）在生态上和进化上合理的假设条件。