Ok... so "difference"... however it is still a random accident.
Im still learning! lol
How then can mutation explain the developement of an irriducible mecanism such as the knee joint?
The knee joint is irreduceable and cannot evolve as it requires four complex parts (Posterior cruciate ligament, Anterior cruciate ligament, Tibia and fuma) to exist simultaniosly and i complex assembly to be able to praform a useful function.