Shanley Daryl P, Sear Rebecca, Mace Ruth, Kirkwood Thomas B L
Henry Wellcome Laboratory for Biogerontology Research, Institute for Ageing and Health, Newcastle University, Newcastle upon Tyne NE4 6BE, UK.
Proc Biol Sci. 2007 Dec 7;274(1628):2943-9. doi: 10.1098/rspb.2007.1028.
Why do women cease fertility rather abruptly through menopause at an age well before generalized senescence renders child rearing biologically impossible? The two main evolutionary hypotheses are that menopause serves either (i) to protect mothers from rising age-specific maternal mortality risks, thereby protecting their highly dependent younger children from death if the mother dies or (ii) to provide post-reproductive grandmothers who enhance their inclusive fitness by helping to care and provide for their daughters' children. Recent theoretical work indicates that both factors together are necessary if menopause is to provide an evolutionary advantage. However, these ideas need to be tested using detailed data from actual human life histories lived under reasonably 'natural' conditions; for obvious reasons, such data are extremely scarce. We here describe a study based on a remarkably complete dataset from The Gambia. The data provided quantitative estimates for key parameters for the theoretical model, which were then used to assess the actual effects on fitness. Empirically based numerical analysis of this nature is essential if the enigma of menopause is to be explained satisfactorily in evolutionary terms. Our results point to the distinctive (and perhaps unique) role of menopause in human evolution and provide important support for the hypothesized evolutionary significance of grandmothers.
为什么女性在远未到全身衰老致使生育在生物学上变得不可能的年龄时，就会通过更年期突然停止生育能力呢？两种主要的进化假说是，更年期要么（i）保护母亲免受特定年龄的孕产妇死亡风险上升的影响，从而在母亲死亡时保护其高度依赖的年幼子女免于死亡，要么（ii）为生育后的祖母提供帮助，她们通过帮助照顾和抚养女儿的孩子来提高其广义适合度。最近的理论研究表明，如果更年期要提供进化优势，这两个因素都必不可少。然而，这些观点需要使用来自在合理“自然”条件下实际人类生活史的详细数据进行检验；出于明显的原因，此类数据极为稀少。我们在此描述一项基于冈比亚非常完整的数据集的研究。这些数据为理论模型的关键参数提供了定量估计，然后用于评估对适合度的实际影响。如果要从进化角度令人满意地解释更年期之谜，这种基于实证的数值分析至关重要。我们的结果指出了更年期在人类进化中独特（也许是独一无二）的作用，并为祖母假设的进化意义提供了重要支持。
