One of the many reasons that Darwin's ideas were rejected is that people simply didn't have a good sense about how much time had passed in the evolution of mice and elephants. It is obvious that tiny changes don't make much difference if you only pay attention over the short term.
Financial planners like to show the effects of compound interest, shocking people into saving. ("If you save only 36 cents per day every day from the time you are 8, assuming 11.4% interest, you will have amassed 7.4 billion dollars by the time you are 113," they might say, or something like that.)
The more history I've read, the more of a radical incrementalist I have become. It is rare that any one year offers much in the way of change. And yet the lives of 20 year olds in 2008 are so vastly different from the lives of 20 year olds in 1008 as to nearly qualify as life on another planet.
This long-term view has made me an optimist twice. Once because I know that an individual may not experience any real change and yet society may change. Science proceeds by the death of scientists, is the quip I believe. But I'm also made an optimist because the rate of change has continued to (incrementally) change: it has accelerated. We're living in a period of time when change is increasingly experienced by individuals across decades and not just by societies across centuries.
Last night, this country nominated a black as a major party candidate for the first time in its 200+ year history. It came about from fairly incremental change and progress. But it is, if you think about it, a pretty radical thing.