Answer:
A father's child, a mother's child, yet no one's son
I have joy in bringing two together, but darning my existence! My life hangs by a thread, filled with ups, downs and resistance!
Ambitious people will climb the social version of this contraption.
Of these everyone has ten, part of two wholes at the arms end. What are they?
They are Dark, and always on the run. without the sun, would be none!
Though not a plant, has leaves. Though not a beast, has spine. Though many wouldn't need this thing, It's more valuable than wine.