Department of Anthropology, University of Massachusetts Amherst, Amherst, MA 01003, USA.
Department of Anthropology, University of Massachusetts Amherst, Amherst, MA 01003, USA; Graduate Program in Organismic and Evolutionary Biology, University of Massachusetts Amherst, Amherst, MA 01003, USA.
J Hum Evol. 2018 Apr;117:33-43. doi: 10.1016/j.jhevol.2017.12.003. Epub 2018 Feb 20.
Sweating is an unusual thermoregulatory strategy for most mammals, yet is critical for humans. This trait is commonly hypothesized to result from human ancestors moving from a forest to a warmer and drier open environment. As soft tissue traits do not typically fossilize, this idea has been difficult to test. Therefore, we used a comparative approach to examine 15 eccrine gland traits from 35 primate species. For each trait we measured phylogenetic signal, tested three evolutionary models to explain trait variation, and used phylogenetic models to examine how traits varied in response to climate variables. Phylogenetic signal in traits varied substantially, with the two traits exhibiting the highest values being gland distribution on the body and percent eccrine vs. apocrine glands on the body. Variation in most traits was best explained by an Ornstein-Uhlenbeck model suggesting the importance of natural selection. Two traits were strongly predicted by climate. First, species with high eccrine gland glycogen content were associated with habitats exhibiting warm temperatures and low rainfall. Second, species with increased capillarization were associated with high temperature. Glycogen is a primary energy substrate powering sweat production and sodium reabsorption in the eccrine gland, and increased capillarization permits greater oxygen, glucose and electrolyte delivery. Thus, our results are evidence of natural selection for increased sweating capacity in primate species with body surface eccrine glands living in hot and dry climates. We suggest that selection for increased glycogen content and capillarization may have been part of initial increases in hominin thermoregulatory sweating capacity.
出汗是大多数哺乳动物不常见的体温调节策略，但对人类来说却是至关重要的。这种特征通常被认为是人类祖先从森林迁移到温暖干燥的开阔环境的结果。由于软组织特征通常不会形成化石，因此这个想法一直难以验证。因此，我们使用了一种比较的方法来研究了 35 种灵长类动物的 15 种外分泌腺特征。对于每种特征，我们测量了系统发育信号，检验了三种进化模型来解释特征变异，并使用系统发育模型来检查特征如何响应气候变量而变化。特征的系统发育信号变化很大，其中两个表现出最高值的特征是身体上的腺分布和身体上的外分泌腺与顶泌腺的比例。大多数特征的变异最好由一个奥尔森-乌伦贝克模型解释，这表明自然选择的重要性。有两个特征与气候强烈相关。首先，具有高外分泌腺糖原含量的物种与具有温暖温度和低降雨量的栖息地有关。其次，毛细血管化增加的物种与高温有关。糖原是一种主要的能量底物，为外分泌腺的汗液产生和钠重吸收提供动力，而毛细血管化的增加则允许更多的氧气、葡萄糖和电解质输送。因此，我们的结果证明了在具有体表外分泌腺的灵长类动物中，自然选择有利于增加在炎热干燥气候下的出汗能力。我们认为，选择增加糖原含量和毛细血管化可能是人类初始增加体温调节出汗能力的一部分。
