Why is evolutions primary mechanism mutation ?

This is a bit of a puzzling request... What is a ground rule? I think it's easy enough to say that there is a lot involved here.There are several kinds of mutations. Ignoring duplications, truncations, reversals, and other things that don't -immediately- cause a change in the organism's real genetic information, point mutations are by far the most common survivable mutations.Shift mutations also occur, but in the case of mammals, result in a dead sperm, useless ovum, etc.Transcriptions might also swap out parts of genes, say, replacing a part of one of mommy's chromosome's with the matching part of one of daddy's, but this wouldn't always be considered a mutation, though it is a factor in evolution.By far the most common, survivable mutations are point mutations. While 'random', some parts of the genetic structure are more susceptible to mutation than others. Thus the overall rate (~100 per generation in humans) might change from species to species like the 'real' rate (~1 per generation in humans) does.Alright, so you have 100 or so genetic errors that make you different from your parents. Likely, 1 or 2 of these has caused a real change - the other 98 causing no change in an actual protein being coded.Is this mutation you have beneficial, harmful, or neutral? Well, since you are alive, it is most likely somewhere between 'slightly harmful' and 'quite beneficial'. If it were 'very harmful' you would probably have been miscarried in your mother's womb, as 70% of pregnancies end.So yes, it's true that most real mutations are in fact harmful. For every human alive today, at least two more died in the womb. Those were the most harmful of them (some do survive to birth, but tend not to live to maturity).