A comment I just left in the "Future Is Wild" boards:
That Darwin's theory explains why things are the way they are, with regards to survival, it doesn't explain the HOW, which is mutation. Mutations occur and natural selection drives the duplication of the mutated genes 'til a new species is differentiated from the old.
However, the nature of how mutations really happen, and how "good" ones that are "prefered" arrive (as we're very keyed in to hating anything "different" ourselves and often shun it in humans or kill it in animals) is what we as humans have not been able to truly see or test. Its hard to test, as mammals have too long a breeding period, and colonial insects (ants and bees) are usually dominated by the queen's genes. Most genes that change behaviours tended to have already been on the planet somewhere, and are only spreading now because we're accidentally spreading them (e.g., "africanized/killer" bees).
The show did a good job of suggesting what natural selection might do, given a set of mutations over X million years to produce said animals, but the fact is that the mutations themselves are what's utterly unpredictable...and truth be told, rather boring by comparison to the end-results we saw.
I consider evolution a fact, but not a law in the Newton/Einstein sense, because evolution can't be used to predict the future with any accuracy since evolution doesn't explain mutations; it only relies on them. It would be like trying to use Einstein to predict something in electrons without the use of calculus.