How Humans Differ from Other Animals in Their Levels of Morphological Variation

Animal species come in many shapes and sizes, as do the individuals and populations that make up each species. To us, humans might seem to show particularly high levels of morphological variation, but perhaps this perception is simply based on enhanced recognition of individual conspecifics relative to individual heterospecifics. We here more objectively ask how humans compare to other animals in terms of body size variation. We quantitatively compare levels of variation in body length (height) and mass within and among 99 human populations and 848 animal populations (210 species). We find that humans show low levels of within-population body height variation in comparison to body length variation in other animals. Humans do not, however, show distinctive levels of within-population body mass variation, nor of among-population body height or mass variation. These results are consistent with the idea that natural and sexual selection have reduced human height variation within populations, while maintaining it among populations. We therefore hypothesize that humans have evolved on a rugged adaptive landscape with strong selection for body height optima that differ among locations.动物物种具有多样的形态与体型，构成各物种的个体及种群亦不例外。于人类而言，我们自身似乎展现出格外显著的形态变异，但这种感知或许仅仅源于相较于异种个体，人类对同种个体的辨识度更高。本研究更客观地探讨了人类与其他动物在体型变异方面的差异。我们对99个人类种群以及848个动物种群（涵盖210个物种）的种群内和种群间的体长（身高）与体重变异水平进行了定量比较。研究发现，相较于其他动物的种群内体长变异水平，人类的种群内身高变异程度较低。但人类的种群内体重变异水平，以及种群间身高或体重变异水平，均未表现出特异性。上述结果与以下观点一致：自然选择与性选择降低了人类种群内部的身高变异，却维持了种群间的身高差异。因此我们提出假说：人类是在崎岖不平的适应性景观中演化而来的，不同地理位置对身高最优值存在强烈的选择压力。