Figure 1. Form space principal component analysis.

The first three PCs in Procrustes form space account for approximately 94% of the total form variance for block 1 and 98% of that for block 2. Chimpanzees (blue trajectory) and humans (black trajectory) have distinct curvilinear ontogenetic trajectories. Blue dots: chimpanzee fetuses (a, b) to neonates (c). Black dots: humans from birth (d) to ~1 y.o. (e), red dots: from ~1 to ~2.5 y.o., green dots: from 2.5 to 5.5 y.o (f). Pink dots: regression estimates at age a, b, c, d, e and f visualized in Figure 2. The 3D reconstructions of blocks 1 and 2 show the landmark and semilandmark configurations (see Figure S1 and Table S1 for complete description). Note the parallel orientations of trajectories between a) and b) in chimps and between d) and e) in humans demonstrates similar developmental pathways within a different anatomical context.