Department of Biology, University of Turku, 20014 Turku, Finland.
Department of Biology, University of Turku, 20014 Turku, Finland.
Curr Biol. 2019 Feb 18;29(4):645-650.e3. doi: 10.1016/j.cub.2018.12.052. Epub 2019 Feb 7.
Recent advances in medicine and life-expectancy gains have fueled multidisciplinary research into the limits of human lifespan [1-3]. Ultimately, how long humans can live for may depend on selection favoring extended longevity in our evolutionary past [4]. Human females have an unusually extended post-reproductive lifespan, which has been explained by the fitness benefits provided from helping to raise grandchildren following menopause [5, 6]. However, formal tests of whether such grandmothering benefits wane with grandmother age and explain the observed length of post-reproductive lifespan are missing. This is critical for understanding prevailing selection pressures on longevity but to date has been overlooked as a possible mechanism driving the evolution of lifespan. Here, we use extensive data from pre-industrial humans to show that fitness gains from grandmothering are dependent on grandmother age, affecting selection on the length of post-reproductive lifespan. We find both opportunities and ability to help grandchildren declined with age, while the hazard of death of women increased greatly in their late 60s and 70s compared to menopausal ages, together implying waning selection on subsequent longevity. The presence of maternal grandmothers aged 50-75 increased grandchild survival after weaning, confirming the fitness advantage of post-reproductive lifespan. However, co-residence with paternal grandmothers aged 75+ was detrimental to grandchild survival, with those grandmothers close to death and presumably in poorer health particularly associated with lower grandchild survival. The age limitations of gaining inclusive fitness from grandmothering suggests that grandmothering can select for post-reproductive longevity only up to a certain point.
医学和预期寿命的进步推动了多学科研究，探索人类寿命的极限[1-3]。最终，人类能活多久可能取决于在我们的进化史中，选择是否有利于延长寿命[4]。女性具有异常延长的生殖后寿命，这一现象可以通过绝经后帮助抚养孙辈带来的适应性好处来解释[5,6]。然而，关于这种祖母照顾是否会随着祖母年龄的增长而减弱，以及是否能解释观察到的生殖后寿命长度的正式测试还没有。这对于理解目前对长寿的主要选择压力至关重要，但迄今为止，这一机制被忽视了，它可能是驱动寿命进化的一个因素。在这里，我们利用来自前工业化时代人类的大量数据表明，祖母照顾的适应性好处取决于祖母的年龄，这影响了对生殖后寿命长度的选择。我们发现，随着年龄的增长，帮助孙辈的机会和能力都在下降，而女性在 60 多岁和 70 多岁时的死亡风险比绝经时大大增加，这意味着对随后的长寿选择逐渐减弱。有 50-75 岁的祖母存在，增加了断奶后孙辈的存活率，证实了生殖后寿命的适应性优势。然而，与 75 岁以上的祖父一起生活对孙辈的存活率不利，那些接近死亡且健康状况可能较差的祖母，尤其是与较低的孙辈存活率有关。从祖母那里获得综合适应度的年龄限制表明，祖母照顾只能在一定程度上选择生殖后长寿。
