Actually, it is called the Law of Gravity. What you are probably referring to is the Theory of General Relativity which attempts to provide an explanation of why gravity exists. Your misunderstanding of the terms and concepts involved has led you to believe that the theory of evolution is on a par scientifically with the existence of gravity. That simply is not the case. There are quite a few so called "missing links" to validate the theory that man has just evolved from a simpler life form.