A mutation is not the cause of evolutionary change. Over the years he has unearthed the bones of an ancient pig as big as a rhino, a six foot tall sheep a twelve foot tall bird and the flat - topped skull of the erect 'Nutcracker man'. And there is no way of avoiding this destiny. For the fateful principle known as the second law of thermodynamics, which stands today as the principal pillar of classical physics left intact by the march of science, proclaims that the fundamental processes of nature are irreversible. Nature just moves one way.
Some comets seem to tire out and die.
However, we know that the stars exist, and we must do our best to account for them. If galaxies didn't exist, we would have no problem explaining that fact. The problem of explaining the existence of galaxies has proved to be one of the thorniest in cosmology. By all rights, they just shouldn't be there, yet there they sit. It's hard to convey the frustration that this simple fact induces among scientist.