there's also this issue of "irreducible complexity" which is really interesting when debating evolution. Think of a mouse-trap. it performas a well-defined action and needs a certain arrangement of several components. According to evolution, things evolve due to survival advantages over previous versions. but does a block of wood with a piece of cheese hold any advantage over just a block of wood? and then a block of wood with a piece of cheese and a spring over a block of wood with cheese? and then a block of wood with a piece of cheese and a spring and a swing-arm?

and those are just things. you also need correct placement and a desired action.

and this is just a simple machine. your body is composed of millions of complex machines, whose many supposed intermediate versions would pose no evolutionary advantage.