4. Puberty presents a new hormonal milieu to the landscape already primed for it in the womb. Testosterone surges to very high levels, and finishes the job already started in the male. Differences in skeletal proportion and density, pelvic shape, lung capacity, muscle size and strength, and the now-obvious secondary sexual characteristics are overwhelming in their remaking of the organism, from hands to feet, from jawbone to kneecaps. These changes are essentially permanent, and they are significant for physical performance, just like the in utero priming of the system.