I do a lot with my hands. We all do. So, let's take a moment and thank those responsible for good hands: our feet, legs and back and our ears.
I used to jump over the part of descriptions of humans that mention "bipedal". Yeah, yeah, we walk on two feet. We can crawl on all fours but we basically walk on two feet. We also dance on two feet, balance precariously on two feet, run, jump and play all sorts of tricky sports on two feet. We don't have elongated arms that balance us with our knuckles on the ground. We don't stand upright once in a while, we do it all the time.
To be able to walk and carry things (which are important in life), we need our hands and arms. That means we need feet and legs and very definitely back muscles to enable a large, bumpy structure to successfully travel and to stand still over the small area of two human feet. Try getting some Legos or an erector set and build something as tall, wide, thick and heavy and balance the whole thing over two bases the size of your feet. No cheating! Outline your feet on a piece of paper and be sure the bases each fit in a foot outline.
Then, of course, we have the problem of locomotion. This creation needs to be able to walk. If you can get that working, move on to running, dancing, basketball, etc. All those back and skeletal muscles have their purpose. It is not easy. You could follow nature and put some sophisticated gyroscopes in the sides of the head, about where the ears are. They may be able to send balancing signals to the back, thighs, hips and feet to keep the whole critter upright.
You can see that the feet, the back muscles and the balance in the ears enable us to use our hands to do things. If you watch over the course of a day, as you cook, type, phone, use a tv remote, set the dials on your washing machine and drive a car, you can appreciate how advanced our hand use is, all from the freedom given us by our other parts that enable us to use our hands for all the good things they do.
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