How would you think natural human flight would be possible?
What do you mean by "natural" and is the context of possibility within or without physics(i.e., reality or fantasy)?
Like how superman can fly without machines he can just fly naturally. And fiction of course but if you think it's possible (like I do) then please feel free to explain :)
Superman violates a number of physical laws when he flies. From conservation of energy and momentum, to fundamental forces interactions. As such his flying is hardly natural.
If you want a human being on Earth to fly in air(other than by falling) without any aids, i.e., "as is", then it's not possible. We have no way of generating enough lift to counteract the gravitational attraction of Earth. We're too heavy and our limbs are too aerodynamic to push enough air mass downwards to keep us afloat.
Look at birds and all the evolutionary changes that were required to allow them to fly. From huge paddle-like upper limbs to catch more air in a stroke, hollow bones to reduce mass, special skeletal structures to attach the flight musculature to, and modified breathing apparatus to maintain the supply of air.
The best we can do is find some denser medium in which the force of buoyancy would suffice. It could be some very dense atmosphere on some other planet, or it could be water on Earth. In both cases a human effectivelly floats, and can "fly" i.e., swim.
Of course, we couldn't/can't breathe then, so it's not a perfect solution either.
What already has been done:
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