For a human to grow wings and fly, this is required:
Increase in heart and lung size (2 or 3 times): in order to handle the vastly increased O2/CO2 exchange and transport of nutrients and waste products such as lactic and uric acids. This would also increase the size of the torso by at least twice the circumference.
A morphing of the arms into wings: wings cannot attach to a human back. There simply is no place to do so.
Attached to the spine their weight and the stresses involved in using them would snap the spine in half.
Attached to the spinal ribs would snap the ribs and get completely in the way of the shoulderblade rotation, rendering your arms useless.
Attached to the shoulderblades would require the arms to flap along with the wings. It is a proven fact that the human form cannot flap its arms fast enough to achieve lift-off.
Loss of most of the legs: your legs account for about 40% of your mass, or about 60 lbs of a 150 lb person, or about 30 lbs. per leg at that weight. Using that as an average, leg weight per foot is roughly 10 lbs. Far too heavy to allow flight ? even hang glider pilots cannot ?tuck? their legs up underneath them for any appreciable amount of time ? they use a leg bag to pull their legs up and back. The legs would have to become spindly stalks ? just like a bird.
Weight of the wing: Allowing for muscle, bone, tendons, blood supply, feathers, etc. it can be easily assumed that a wing would be comparable in weight to the human leg, or about 10 lbs. per foot.
The human form cannot be supported in flight by less than 22-24 feet of wingspan.
That?s a 12 foot wing.
At about 100: 120 lbs. per wing, or 200 ? 240 lbs. of wing on your now grossly enlarged torso.
And all that weight is now bearing down on your spindly sticks of legs.
Which snap like twigs the minute you try to run on them for any reason.
The neck: in order to allow for forward vision during flight the neck would have to extend and permanently crane backwards (like a bird) to allow you to see forward, and not constantly down. Using your head to view forward in a normal human position would be painful and uncomfortable,
So in wrap-up: a human avian would be, in short, a mutated, misshapen freak. Huge torso, no arms or hands, bird legs, elongated neck, and eating everything in sight just to satisfy the metabolic demands from the muscular exertion.