but there are also different mechanisms at work, and this is where I've modified my opinion.
As I understand what you've said, the only difference in mechanisms is that the "tendency towards stasis" no longer operates once a population has divided. In other words, there are no additional or different mechanisms that operate at the "macro" evolutionary level, but simply one mechanism that is no longer operative. Is my understanding accurate?
Those who would sacrifice an essential liberty for a temporary security will lose both, and deserve neither. -- Benjamin Franklin