Last universal common ancestor

The most recent ancestral population shared by all organisms living today. Its existence is inferred from universal features of cellular life, though it was not necessarily a single organism.

Universal common ancestry: The hypothesis that all living organisms descend from a common ancestral population. LUCA is the most recent shared ancestor implied by this broad evolutionary relationship.
Horizontal gene transfer: The movement of genetic material between organisms outside parent-to-offspring inheritance. Gene exchange among early microbes can blur the branching history used to infer LUCA.
RNA world: A hypothesis that early life relied on RNA for both genetic information and catalytic activity. It concerns a stage before DNA-and-protein biology, potentially preceding LUCA.
Deep-time phylogeny: The reconstruction of evolutionary relationships extending across the earliest history of life. Ancient gene histories can disagree, making LUCA's position and ancestry difficult to resolve.
Three-domain system: A classification dividing cellular life into Bacteria, Archaea, and Eukarya. LUCA is the inferred ancestor preceding the deep separations represented by these domains.
Phylogenetics: The study of evolutionary relationships using inherited characteristics, especially molecular sequences. Phylogenetic methods infer the deep branching relationships that place LUCA before major lineages diverged.
Ancestral sequence reconstruction: The computational inference of ancestral DNA, RNA, or protein sequences from living descendants. Researchers use it to estimate molecular features that may have been present in LUCA.
Origin of life: The emergence of self-sustaining chemical systems capable of evolution from nonliving matter. LUCA was already part of life's history, so its origin is distinct from life's first emergence.
Archaea: A domain of single-celled organisms distinct from bacteria and eukaryotes. Archaeal traits and genes inform debates about LUCA's biology and the origins of eukaryotes.
Universal tree of life: A model of evolutionary relationships connecting all known cellular organisms. LUCA anchors the common root from which the tree's living branches ultimately descend.

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