Here is an article from the excellent scientists at Answers in Genesis about a study on natural selection adaptations that occurred rather quickly after relocating a species of island lacertas to a neighboring islet. Most notable in my opinion is the reappearance of the cecal valve in order to allow microorganisms more time to breakdown a diet consisting of much higher percentage of plant matter than that of the population on the original island. We are talking about a documented appearance or resurgence of an entire functional organ throughout an entire population occurring within a few DECADES. How fast can an adaptation occur? Although this does not necessarily lend itself to the reductive microevolution theory, it certainly adds credence to the mass “speciation” or we would say “variance among kinds” that must have taken place quickly after the Genesis flood. There would have certainly been countless new habitats and microenvironments at that point and animal life would have undergone a myriad of changes in a short amount of time to get to the point that we see today. If a population of lizards, when introduced to a different habitat can undergo a drastic change before our eyes, than certainly 4,000 years of change could account for the speciation in our current animal kingdom.
http://www.answersingenesis.org/articles/aid/v3/n1/life-designed-to-adapt