[VadeRetro]

VadeRetro: What mechanism prevents changes from ever being beneficial? What mechanism prevents changes from adding up? What evidence do you have for these assertions?

shawne: what evidence do you have to counter?

First of all, when you assert that "no changes are beneficial," you imply the existence of some mechanism to prevent some random change from being beneficial to the organism. Otherwise, why wouldn't a change be lucky once in a blue moon? Similarly, when you assert that "no random changes accumulate," you imply the existence of some mechanism that prevents same, since you have already admitted the occurrence of said random changes. If you can't come up with a plausible and defensible mechanism in each case, I'm not going to give you a free pass just because you'd like to slough the burden of proof on me. You remain tasked with identifying mechanisms and with providing evidence for their existence. Your request for a free pass is denied.

As it happens, however, there is a vast amount of evidence that microevolutionary changes accumulate to macro.

Tempo and Mode of Speciation (A slide show for newbies like yourself)
29 Evidences for Macroevolution (Good but long overview)
Some links on "Where are the transitionals?"

There's plenty more, but try to actually follow the links and read on that for a bit.