An experiment started twenty years ago on E. Coli bacteria reveals proof of evolution. A single strain of E. Coli was divided into twelve separate containers, never again to be mixed. Each day for twenty years each strain was supplied with a limited quantity of glucose for sustenance. The population would quickly expand, metabolizing all the available glucose, then begin to starve to death. Before all starved to death, a small sample of the survivors was taken out each day and placed in a new container with the same limited supply of glucose. After twenty years of this all twelve strains became more highly adapted to efficiently metabolizing glucose in such a way as to survive longer and longer on the same limited supply as compared to the starting strain, and each strain but two adapted in completely different ways. Two strains, by chance, adapted in exactly the same way via the exact same mutation.
But here's the important part: One strain became super adapted, far surpassing the other eleven, not only by doing as the others did, but by discovering a way (also via mutation) not only to more efficiently metabolize the limited supply of glucose, but by also discovering a way (also via mutation) to metabolize citrate as well, an incidental component of the glucose feed fed to all twelve colonies from the beginning, but which E. Coli can ordinary not make use of as food. This one colony became super adapted to the conditions of the experiment via mutation by "figuring out" (in the evolutionary sense), after twenty years (about 30,000 generations, or the equivalent of one million years for humans), how to metabolize citrate.
This strain reproduced each successive day to enormous numbers, and their population growth continued far beyond the point all the glucose was gone, and other colonies had died out from starvation, due to this one adaptation.
Furthermore - and here comes the real pay off - it was not a mere single mutation which permitted it to metabolize citrate for energy, but TWO independent mutations which had to exist simultaneously for E. Coli to metabolize citrate.
