Robusticity, as measured by a ratio of bone thickness to bone length, is fundamentally determined by biomechanical stress and the presence of androgens. There is a cline of less robusticity as one goes across the various species of Homo (H. Erectus had the most muscle, H. Sapiens has the least).

Early Modern Homo Sapiens had more robust arms and legs than us today, simply because they walked more, and perhaps on rugged and hilly terrain. They were also engaging in throwing activities…