Definition
Hominin refers to any member of the human evolutionary clade — every species, living or extinct, that is more closely related to modern humans than to chimpanzees. The clade begins after the lineage split from our last common ancestor with Pan roughly 6–8 million years ago and ends with Homo sapiens.
The term replaces the older, broader hominid, which under modern molecular taxonomy now refers to the entire great-ape family (humans, chimps, gorillas, orangutans). When Bernard Wood and most contemporary paleoanthropologists say hominin, they mean strictly our side of the chimp-human split — Sahelanthropus, Ardipithecus, Australopithecus, Paranthropus, every Homo species, and any unnamed bones that may yet join the list.
Why it matters
How it works
A fossil is classified as hominin when its anatomy shows features shared exclusively with the post-split human lineage — a bipedal pelvis, a non-honing canine, a foramen magnum positioned for upright posture — or when its position in time and place rules out membership in the chimp lineage. Genetic data, where preservation allows, confirms or revises these placements.
The boundary between hominin and non-hominin matters most near the root. Sahelanthropus tchadensis (~7 mya) sits close to the split, and whether it is a hominin, a stem chimp, or close to the last common ancestor is still debated. As you move forward in time, the assignments become firmer.