While it is undeniably true that at every stage of his life Bow has expended more energy on locomotion than Sword has, I still have my doubts about the conclusions in the article I linked yesterday.
I think that Bow expends more energy than we do even when at rest.
Bow has a much higher metabolism than we do, and this is largely due to his greater muscle mass.
Whether moving or at rest, Bow has to burn energy to maintain muscle mass. This also makes him a much more energetic participant in everything he does, and sometimes it seems he is just bouncing off the walls.
When we look at the video above, it is clear that Sword is much slower than Bow is, and that the lower energy cost of her locomotion is largely due to the fact that she has less muscle than Bow. In a competition for speed or endurance, Bow could beat her, no matter what form of locomotion he happens to be using. It's the fact that he is designed to burn more energy all the time that makes him a more efficient runner, climber and go-getter. Even when he has to hold Sword's hand and is awkwardly walking on two feet and one hand's knuckles, he is faster than Sword. He slows down to accommodate her walking gait, because they are walking together.
Bow loves to listen to music. He has been listening to the The Sound of Music since he was very little, and when Lady Gaga gave her tribute to the fifty year old musical at the Oscars, Bow became a very big fan of that Lady Gaga clip. He asks to watch it very frequently. He asked for it yesterday. And even this morning he spelled out: תני לי לשמוע מוזיקה . "Let me listen to music." When I asked him what kind of music he wanted to hear, he replied::גגה "Gaga."
When Bow listens to music, every part of him is involved in the process of appreciating the music. He bounces off the concrete floor as if he were on a trampoline. He sways with the music, pounds out the beat, and comes to a crescendo of activity at the climax. And then stops.
Bow's reaction to Julie Andrews talking is much more quiet, calm and respectful than his frenzied involvement with Lady Gaga singing. But even when at rest and fondly sticking out his tongue at Julie Andrews -- a sign of affection -- he is probably burning more energy than the average fan of musicals who is human when at rest.
So I could postulate the hypothesis that humans developed bipedalism to help us burn less energy when listening to music, but how plausible is that? Isn't it much more likely that after we found less difficult ways to get food, our muscles and bones became degenerate, because the weaker among us were not culled out, and we began to have a lower metabolism, because our muscle mass was much lower? After all, there is evidence that the bones of hunter gatherers are much thicker than those of agricultural peoples.
Whatever the reason, Bow definitely expends more energy when listening to music than the average human being. High energy expenditure is as much caused by a naturally high metabolism as it aids in developing higher muscle mass in those not originally blessed with this trait. That makes ferreting out which came first a little difficult.