Which concept is associated with all organisms sharing a common ancestor in the context of cladistics?

The concept of common descent is fundamental in the study of cladistics, as it posits that all organisms can be traced back to a shared ancestor. Cladistics focuses on classifying living organisms based on their evolutionary history, specifically by analyzing characteristics that are inherited from common ancestors. Using this framework, organisms are grouped into clades, which are branches that represent these shared ancestral lines. This approach helps researchers understand the evolutionary relationships among various species and construct evolutionary trees (phylogenies) that illustrate these connections.

The other concepts presented do not directly convey the idea of a shared ancestral lineage. Evolutive trait refers to characteristics that evolve over time within a species, but it does not specifically address the common ancestry of all organisms. The theory of relics may imply the survival of certain traits from ancestors but doesn't provide a framework for understanding how all organisms are interconnected through common descent. Species relevance may suggest how different species are significant in various contexts, but it lacks the implication of shared ancestry that common descent embodies.