One way for a species to store the information it needs for survival is in dna. Dna works for information acquired over the life-time of the species; relatively consistent over life-time of species. Dna deals with aspects of world that are consistent over very long time periods. Memory exists because dna is not enough; dna is for things consistent over long periods; memory and learning for things that change over short periods of time. Animals could be predators one day, prey the next. Storing information about world would be pointless. Predators equally distributed in every direction, food always in same place. Then, all responses could be coded into dna and learning during your life would not be necessary. A partially random, partially systematic world (real world) Memory makes sense; change things on a smaller time scale but not worth to be in dna. Makes sense for our behaviour to be guided by that structure.