What is the essence of the law of irreversibility of evolution?

Organisms, populations and species that have arisen in the course of evolution cannot return to the previous state of their ancestors, since each evolutionary change is a combination of many independently emerging and picked up by selection rearrangements of heredity. It should also be taken into account that it is not individuals that evolve, but populations; not individual genes and traits are selected, but gene complexes, and whole gene complexes are controlled by selection. Therefore, it is difficult to expect that the same complex of genetic properties will repeat once again, returning the group back to its original state.