Mild diseases and moderate stressors are seemingly harmless and are therefore often assumed to have negligible impact on Darwinian fitness. Here we argue that the effects of ‘benign’ parasites and other moderate stressors may have a greater impact on lifespan and other fitness traits than generally thought. We outline the ‘accumulating costs’ hypothesis which proposes that moderate strains on the body caused by mild diseases and other moderate stressors that occur throughout life will result in small irreversible ‘somatic lesions’ that initially are invisible (i.e., induce ‘hidden’ costs). However, over time these somatic lesions accumulate until their summed effect reaches a critical point when cell senescence and malfunction begin to affect organ functionality and lead to the onset of degenerative diseases and aging. We briefly discuss three potential mechanisms through which the effects of moderate strains (e.g., mild diseases) could accumulate: accelerated telomere shortening, loss of repetitious cell compartments and other uncorrected DNA damage in the genome. We suggest that telomere shortening may be a key candidate for further research with respect to the accumulating costs hypothesis. Telomeres can acquire lesions from moderate strains without immediate negative effects, lesions can be accumulated over time and lead to a critically short telomere length, which may eventually cause severe somatic malfunctioning, including aging. If effects of mild diseases, benign parasites and moderate stressors accrued throughout life can have severe delayed consequences, this might contribute to our understanding of life history strategies and trade-offs, and have important implications for medicine, including consideration of treatment therapies for mild (chronic) infections such as malaria.

中文翻译：

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累积成本假说——更好地理解看似轻微的疾病和其他中度压力源的延迟“隐藏”成本

轻度疾病和中度压力源看似无害，因此通常被认为对达尔文健康的影响可以忽略不计。在这里，我们认为“良性”寄生虫和其他中度压力源对寿命和其他健康特征的影响可能比一般认为的更大。我们概述了“累积成本”假说，该假说认为轻度疾病和其他终生发生的中度压力源对身体造成的适度压力将导致最初不可见的小的不可逆“躯体损伤”（即，诱发“隐藏”成本） . 然而，随着时间的推移，这些体细胞损伤会不断累积，直到它们的总和达到临界点，此时细胞衰老和故障开始影响器官功能并导致退行性疾病和衰老的发生。我们简要讨论了三种潜在机制，通过这些机制，中度菌株（例如，轻度疾病）的影响可以累积：加速端粒缩短、重复细胞区室的丢失和基因组中其他未纠正的 DNA 损伤。我们建议端粒缩短可能是关于累积成本假设的进一步研究的关键候选者。端粒可以从中等应变中获得损伤，而不会立即产生负面影响，损伤会随着时间的推移而累积并导致端粒长度极短，最终可能导致严重的躯体功能障碍，包括衰老。如果轻度疾病、良性寄生虫和终生累积的中度压力源的影响可能会产生严重的延迟后果，这可能有助于我们理解生活史策略和权衡，