The second revolution gave rise to the modern synthesis.
Molecular biology explained how the basis of heredity in all species is encoded in molecules of DNA made of just four basic constituents.*
In the first revolution, Darwin tells us that the origin of species, the diversity of all life on earth came from some warm little pond. This was possible because of natural selection. It was quickly discovered that natural selection (the fittest survive) could not have created all the new forms of life. At best it only acted on existing forms of life. No one knew what natural selection was acting on.
Is this a problem for natural selection? No, not in Darwinian Fizzbin. Darwinists are committed to this game and the rules can be change and distorted in every which way to make Darwinism win. The Darwinists’ response would be “This is how science work. Knowledge is built incrementally and as science advances the gaps in our knowledge are filled.” The problem with that argument is that it is a Fizzbin misdirection.