Okay, but that's not what I asked. If you agree that tiny changes can occur within the genetic code and that these small changes can make almost imperceptible changes to the offspring, what factor limits these tiny changes from adding up, over thousands, hundreds of thousands, (or even millions), of years into what you would term, "macroevolution".
While it's very clear to us that cats always produce cats, it's equally clear that the cats produced today are, many times, greatly dissimilar to cats produced many thousands of years ago. If anyone is waiting around for a dog to give birth to something which is other than a dog, they can put their time to better use because this simply isn't going to happen. That's not the way evolution works.
When you buy a car and drive it home from the dealer, you'll notice that every few seconds, the tenths indicator, (rightmost digit), on the odometer changes. The whole series of digits don't all flip at one time. It starts with several small changes at the rightmost digit. But eventually, those changes add up and the next digit flips. That's more or less the way evolution works. But to say that macroevolution doesn't occur is pretty much like saying that those small changes to the rightmost digit will never add up to the point that they affect a change at the leftmost digit. We know they do and we know this for two reasons. First, that's the way the mechanism is designed to work. And secondly, we can observe this to occur. Evolution isn't quite so convenient. We can peek into the mechanism, but observing macroevolution, as it occurs, simply isn't in the cards. Macroevolution takes a bit more time than most of us have to spare. Even among single-celled organisms, it can take a very long time for all of the small changes to add up into a change significant enough to be readily apparent. You need to think in terms of hundreds of thousands of years or more. And evolution is not a linear process. A species can go for a considerable period of time without any notable changes. It usually requires some new challenge presented by the environment to spawn a change.
Hopefully, with that behind us, the question will be less murky now. What factor do you see as the limitation preventing multiple microevolutionary events from adding up to a macroevolutionary change? What keeps the rightmost digits on the evolutionary odometer from ever affecting the leftmost digits?