Wells Jonathan C K, Pomeroy Emma, Stock Jay T
Childhood Nutrition Research Centre, Population Policy and Practice Research and Teaching Department, UCL Great Ormond Street Institute of Child Health, London, United Kingdom.
Department of Archaeology, University of Cambridge, Cambridge, United Kingdom.
Front Physiol. 2021 Aug 23;12:696516. doi: 10.3389/fphys.2021.696516. eCollection 2021.
The emergence of the capacity to digest milk in some populations represents a landmark in human evolution, linking genetic change with a component of niche construction, namely dairying. Alleles promoting continued activity of the enzyme lactase through the life-course (lactase persistence) evolved in several global regions within the last 7,000 years. In some European regions, these alleles underwent rapid selection and must have profoundly affected fertility or mortality. Elsewhere, alleles spread more locally. However, the functional benefits underlying the rapid spread of lactase persistence remain unclear. Here, we set out the hypothesis that lactase persistence promoted skeletal growth, thereby offering a generic rapid solution to childbirth complications arising from exposure to ecological change, or to new environments through migration. Since reduced maternal growth and greater neonatal size both increase the risk of obstructed labour, any ecological exposure impacting these traits may increase maternal mortality risk. Over many generations, maternal skeletal dimensions could adapt to new ecological conditions through genetic change. However, this adaptive strategy would fail if ecological change was rapid, including through migration into new niches. We propose that the combination of consuming milk and lactase persistence could have reduced maternal mortality by promoting growth of the pelvis after weaning, while high calcium intake would reduce risk of pelvic deformities. Our conceptual framework provides locally relevant hypotheses to explain selection for lactase persistence in different global regions. For any given diet and individual genotype, the combination of lactase persistence and milk consumption would divert more energy to skeletal growth, either increasing pelvic dimensions or buffering them from worsening ecological conditions. The emergence of lactase persistence among dairying populations could have helped early European farmers adapt rapidly to northern latitudes, East African pastoralists adapt to sudden climate shifts to drier environments, and Near Eastern populations counteract secular declines in height associated with early agriculture. In each case, we assume that lactase persistence accelerated the timescale over which maternal skeletal dimensions could change, thus promoting both maternal and offspring survival. Where lactase persistence did not emerge, birth weight was constrained at lower levels, and this contributes to contemporary variability in diabetes risk.
某些人群中消化牛奶能力的出现是人类进化中的一个里程碑，将基因变化与生态位构建的一个组成部分即乳制品业联系了起来。在过去7000年里，促进乳糖酶在整个生命过程中持续活性（乳糖酶持续性）的等位基因在全球多个地区进化出来。在一些欧洲地区，这些等位基因经历了快速选择，必定对生育力或死亡率产生了深远影响。在其他地方，等位基因传播的范围更局限。然而，乳糖酶持续性快速传播背后的功能益处仍不清楚。在此，我们提出一个假说，即乳糖酶持续性促进骨骼生长，从而为因接触生态变化或通过迁移进入新环境而产生的分娩并发症提供一个通用的快速解决方案。由于母亲生长减缓以及新生儿体型增大都会增加难产风险，任何影响这些特征的生态暴露都可能增加母亲的死亡风险。经过许多代，母亲的骨骼尺寸可以通过基因变化适应新的生态条件。然而，如果生态变化迅速，包括迁移到新的生态位，这种适应性策略将会失效。我们认为，饮用牛奶和乳糖酶持续性相结合可以通过促进断奶后骨盆的生长来降低母亲死亡率，而高钙摄入会降低骨盆畸形的风险。我们的概念框架提供了与当地相关的假说，以解释不同全球区域对乳糖酶持续性的选择。对于任何给定的饮食和个体基因型，乳糖酶持续性和饮用牛奶相结合会将更多能量转移到骨骼生长上，要么增加骨盆尺寸，要么使骨盆尺寸免受恶化的生态条件影响。乳制品业人群中乳糖酶持续性的出现可能帮助早期欧洲农民迅速适应北纬地区，东非牧民适应突然的气候变化转向更干燥的环境，以及近东人群抵消与早期农业相关的身高长期下降。在每种情况下，我们假设乳糖酶持续性加速了母亲骨骼尺寸能够变化的时间尺度，从而促进母亲和后代的生存。在没有出现乳糖酶持续性的地方，出生体重被限制在较低水平，这导致了当代糖尿病风险的差异。
