Jantz R L, Meadows Jantz L
Department of Anthropology, University of Tennessee, Knoxville, Tennessee, 37996-0720.
Am J Phys Anthropol. 2017 Jun;163(2):252-263. doi: 10.1002/ajpa.23203. Epub 2017 Mar 20.
The pattern of static and secular allometry was examined in a time series of limb bone lengths from individuals with birth years ranging from 1840 to 1989. The main hypothesis investigated was that secular changes in limb proportions, as seen in changes in the brachial and crural indices, can be explained by allometric responses to increasing size.
Maximum lengths of humerus, radius, femur, and tibia were obtained from 19th and 20th centuries identified skeletons. Allometry was investigated on two levels, static and secular. Static allometry was defined as average allometry within 20-year birth cohorts, and secular allometry as allometry among birth year cohorts. Allometry was assessed by extracting eigenvectors from covariance matrices of log transformed variables. Departures from allometry were examined using shape variables, and principal components of minor axes.
Static covariance matrices were homogeneous. Eigenvectors extracted from the secular covariance matrix showed important departures from static allometry, particularly a much stronger negative allometry of the humerus and a stronger positive allometry of the tibia. Shape analysis showed that relative humerus length decreased significantly over the time period examined and relative tibia length increased. The last principal component, which combined aspects of the brachial and crural index, showed the highest variation among birth year cohorts.
The results demonstrate that the secular changes in limb proportions cannot be explained by allometric responses to increasing size alone. The majority of variation among birth cohorts is found on the last PC and that suggests that canalized development has been disrupted by the unique environment in which modern Americans now live.
研究了出生年份从1840年至1989年的个体四肢骨骼长度时间序列中的静态和长期异速生长模式。所研究的主要假设是，四肢比例的长期变化，如臂指数和腿臂指数的变化，可以通过对体型增大的异速生长反应来解释。
从19世纪和20世纪已鉴定的骨骼中获取肱骨、桡骨、股骨和胫骨的最大长度。在静态和长期两个层面研究异速生长。静态异速生长定义为20年出生队列内的平均异速生长，长期异速生长定义为出生年份队列间的异速生长。通过从对数变换变量的协方差矩阵中提取特征向量来评估异速生长。使用形状变量和短轴主成分检查异速生长的偏差。
静态协方差矩阵是同质的。从长期协方差矩阵中提取的特征向量显示出与静态异速生长有重要偏差，特别是肱骨的负异速生长更强，胫骨的正异速生长更强。形状分析表明，在所研究的时间段内，相对肱骨长度显著下降，相对胫骨长度增加。结合臂指数和腿臂指数各方面的最后一个主成分在出生年份队列间显示出最高的变异性。
结果表明，四肢比例的长期变化不能仅通过对体型增大的异速生长反应来解释。出生队列间的大部分变异存在于最后一个主成分上，这表明现代美国人所处的独特环境扰乱了发育的稳定性。
