Department of Biology, Norwegian University of Science and Technology (NTNU), Norway.
Exp Gerontol. 2013 Apr;48(4):408-13. doi: 10.1016/j.exger.2013.02.001. Epub 2013 Feb 9.
Life history theory proposes that menopause is either an epiphenomenon or an adaptation. The most recent adaptive hypothesis proposes that menopause in humans has evolved because of conflict between reproducing generations (RCH). Overlapping reproduction between generations may impose fitness costs to older and younger females who co-breed. However, it has yet to be demonstrated by using a measure of evolutionary fitness (i.e. grandchildren). Here, we tested the RCH by using multigenerational life-history data of historical Norwegian women. Our results indicate that both generations seem to experience some fitness benefits with co-breeding (i.e. reproductive overlap and cohabit). This was because both younger and older females who co-bred had more grandchildren than those who did not co-breed. We suggest that younger females may partly had enhanced fitness because they copied behaviour of females of the older generation. Our results do not support the hypothesis that reproductive conflict between generations explains the evolution of menopause in women. Our results, taken together with the growing evidence against several assumptions of the RCH, indicate that 1) the decline in follicle number has no marked increase in women as they reach the age of 38 years; 2) humans do not have an abrupt decline in fertility at mean age of 38 years; 3) menopause is not unique to humans; and 4) there are not high numbers of individuals surviving to older adulthood during our evolutionary past. Finally, we discuss an alternative point of view suggesting that menopause might be understood in the light of both ageing in general as well as our increased lifespan.
生命史理论提出，绝经要么是一种偶然现象，要么是一种适应。最近的适应性假说提出，人类的绝经是由于生殖代之间的冲突（RCH）而进化的。代际之间的重叠繁殖可能会给共同繁殖的老年和年轻女性带来适应度成本。然而，这还需要通过使用进化适应度的衡量标准（即孙子孙女）来证明。在这里，我们使用挪威历史女性的多代生命史数据来检验 RCH。我们的研究结果表明，两代人似乎都从共同繁殖中获得了一些适应度优势（即繁殖重叠和同居）。这是因为共同繁殖的年轻和年老女性比不共同繁殖的女性有更多的孙子孙女。我们认为，年轻女性的部分适应度可能有所提高，因为她们复制了年长一代女性的行为。我们的研究结果不支持生殖代之间的冲突解释女性绝经进化的假说。我们的研究结果，加上越来越多的证据反对 RCH 的几个假设，表明 1）随着女性年龄达到 38 岁，卵泡数量的下降并没有明显增加；2）人类的生育能力在 38 岁的平均年龄没有突然下降；3）绝经并非人类所特有；4）在我们的进化历史中，没有大量个体能够存活到老年。最后，我们讨论了一种替代观点，即绝经可以从一般衰老和我们寿命延长的角度来理解。
