The increase in lower/upper limb bone length and strength proportions in adult humans compared to most other anthropoid primates is commonly viewed as an adaptation to bipedalism. The ontogenetic development of femoral to humeral proportions is examined here using a longitudinal sample of 20 individuals measured radiographically at semiannual or annual intervals from 6 months of age to late adolescence (a subset of the Denver Growth Study sample). Anthropometric data (body weights, muscle breadths) were also available at each examination age. Results show that while femoral/humeral length proportions close to those of adults are already present in human infants, characteristically human femoral/humeral diaphyseal strength proportions only develop after the adoption of bipedalism at about 1 year of age. A rapid increase in femoral/humeral strength occurs between 1 and 3 years, followed by a slow increase until mid-late adolescence, when adult proportions are reached. When age changes in material properties are factored in, femoral strength shows an almost constant relationship to body size (body mass.bone length) after 5 years of age, while humeral strength shows a progressive decline relative to body size. Femoral/humeral length proportions increase slightly throughout growth, with no apparent change in growth trajectory at the initiation of walking, and with a small decline in late adolescence due to later growth in length of the humerus. A sex difference in femoral/humeral strength proportions (females greater) but not length proportions, develops early in childhood. Thus, growth trajectories in length and strength proportions are largely independent, with strength proportions more responsive to actual changes in mechanical loading. A cross-sectional ontogenetic sample of baboons (n=30) illustrates contrasting patterns of growth, with much smaller age changes in proportions, particularly strength proportions, although there is some indication of an adaptation to altered limb loadings early in baboon development.

中文翻译：

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对两足动物的个体适应：与狒狒相比，人类的股骨到肱骨长度和力量比例的年龄变化。

与大多数其他类人猿灵长类动物相比，成年人下/上肢骨长度和强度比例的增加通常被认为是对两足动物的适应。此处使用20名个体的纵向样本，以从6个月大到青春期的半年度或年度间隔进行X射线照相术（从Denver生长研究样本中抽取一部分），以纵向方式检查了股骨至肱骨的个体发育。在每个检查年龄也可获得人体测量数据（体重，肌肉宽度）。结果表明，尽管人类婴儿中已经存在接近成年人的股骨/肱骨长度比例，但典型的人类股骨/肱骨干phy端强度比例仅在大约1岁时采用双足后才发展。股骨/肱骨力量在1至3年之间迅速增加，然后缓慢增加直到青春期中期，直到达到成年人的比例。如果考虑到材料特性的年龄变化，则股骨强度在5岁后显示出与体重（体重×骨长）几乎恒定的关系，而肱骨力量则相对于体型逐渐下降。股骨/肱骨长度比例在整个生长过程中略有增加，在步行开始时生长轨迹没有明显变化，并且由于肱骨长度的后期生长，青春期后期略有下降。股骨/肱骨力量比例的性别差异（女性更大）但长度比例没有性别差异，这是在儿童期早期发展的。从而，长度和强度比例的增长轨迹在很大程度上是独立的，强度比例对机械载荷的实际变化更敏感。狒狒的横截面个体发育样本（n = 30）显示了相反的生长方式，年龄比例，特别是力量比例的年龄变化小得多，尽管有迹象表明在狒狒发育早期适应了肢体负荷的改变。