One of the biggest claims of those who disagree with the 'theory' of evolution is that we can't see it happening. Therefore (so they say) it isn't any more valid than other 'theories' of how species came to exist. You know what I say to that? Spend some time watching cichlids in Lake Victoria.
Here's how it works:
The deeper you go, the darker water gets, but there isn't just less light. Light is filtered out by wavelength, meaning certain colors can only penetrate so deeply into the water column. How deep a certain color of light penetrates depends on how cloudy, or "turbid," the water is. Blue is filtered out pretty quickly, meaning the color blue is only visible in shallower waters, whereas red light is the only light that penetrates to the deep. This means that there are habitats which are mostly 'blue-lit,' a.k.a shallow ones, and ones that are 'red-lit,' a.k.a deep ones.
It turns out that fish that tend to live at certain depths have developed differences in their ability to see colors - they're better at seeing the color most available at their depth. So deeper fish see red better, shallow fish see blue better. This difference in vision could be separating red-bodied cichlids from blue-bodied ones to form new species, according to a study led by Norihiro Okada, an evolutionary biologist at the Tokyo Institute of Technology.
The study, published in the October 2nd edition of Nature, looks at the DNA of cichlids from shallow and deeper waters. Okada and his team show that fish have accumulated separate genetic changes based on how deep they live. Accumulation of genetic differences means that the fish aren't interbreeding, although they are biologically capable of doing so. This 'speciation' is only happening in areas of the lake where blue light is slowly filtered, leaving a large blue-lit area and a large red-lit area, so the fish have enough space to live and breed separately. In areas with high turbidity where the blue-lit zone is smaller, the two groups of fish intermingle and interbreed. They also show that red-lit females prefer red males and blue-lit females prefer blue males. Taken together, these results strongly support that changes in the fish's vision are splitting them into two species - right before our eyes (sorry, I couldn't resist the pun).
So there you go - Evolution in action. How do you like 'dem apples!