Where's the evolution?
The physics of light affects not just how blue water looks to us, but how the animals living in the world's oceans, lakes, and rivers are able to find food and each other — and this, in turn, can impact their evolution. Natural selection favors traits that perform well in local environmental conditions. Many fish species, for example, have evolved vision that is specifically tuned to see well in the sort of light available where they live. But even beyond simple adaptation, the physics of light can lead to speciation. In fact, biologists recently demonstrated that the light penetrating to different depths of Africa's Lake Victoria seems to have played a role in promoting a massive evolutionary radiation. More than 500 species of often brightly colored cichlid fish have evolved there in just a few hundred thousand years!
