Irreversibility of evolution means that a new, more developed life form that has arisen cannot return to the beginning of its development. For example, reptiles cannot become amphibians again. Also, for example, if living organisms return again to the aquatic environment, they will not become fish (cetaceans are mammals, although they live in water).
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.