A scientist discovers a novel entity exhibiting complex organic molecules, compartmentalization, and energy transformation. However, it lacks a definitive cellular structure and doesn't demonstrate heritability. Which characteristic of life is MOST definitively absent in this entity?

A researcher observes an isolated system containing complex organic molecules undergoing spontaneous self-assembly into membrane-bound structures. These structures exhibit rudimentary metabolism but no reproduction or heritability. Which characteristic of life is the MOST significant barrier preventing these structures from being classified as living organisms?