Yet it's the same sock. In relation to its looks and in relation to its partner on your other foot, it is still the same sock. Here philosophers can apply Plato's archetypal ideas of Sameness and Difference. The sock is entirely different from the original as far as the wool goes, but its shape has remained the same. It never becomes a different sock, despite the radical material alteration.
Form is thus visible shape, and the shaping force of the visible.
A human body is like that sock, sloughing off its cells, changing its fluids, fermenting utterly fresh cultures of bacteria as others pass away. Your material stuff through time becomes altogether different, yet you remain the same you. Not one square inch of visible skin, not one palpable ounce of bone is the same, yet you are not someone different. There seems to be an innate image that does not forget your basic paradigm and that keeps you in character, true to yourself. The idea of DNAseems too tight to hold the psychic dimensions of our unique image.