So why does science regard gravity as a "law" rather than a theory? In truth evolution should be considered a hypothesis rather than a theory. A theory is "an explanation of a set of related observations or events based upon proven hypotheses and verified multiple times by detached groups of researchers." I am unaware of any of Darwin's hypotheses being proven.
http://wilstar.com/theories.htm
"I am unaware of any of Darwin's hypotheses being proved. "
Well for starts, there is the presumption that there must be some sort of physical "hereditary information" passed from a parent to offspring. Later proved true by James Watson & Francis Crick in 1953 with the discovery of DNA.