The creation of free neutrons by electron capture during the rapid collapse to high density of a supernova core along with quick assembly of some neutron-rich seed nuclei makes the r -process a primary nucleosynthesis process, a process that can occur even in a star initially of pure H and He. This in contrast to the B FH designation which is a secondary process building on preexisting iron. Primary stellar nucleosynthesis begins earlier in the galaxy than does secondary nucleosynthesis. Alternatively the high density of neutrons within neutron stars would be available for rapid assembly into r -process nuclei if a collision were to eject portions of a neutron star, which then rapidly expands freed from confinement. That sequence could also begin earlier in galactic time than would s -process nucleosynthesis; so each scenario fits the earlier growth of r -process abundances in the galaxy. Each of these scenarios is the subject of active theoretical research. Observational evidence of the early r -process enrichment of interstellar gas and of subsequent newly formed stars, as applied to the abundance evolution of the galaxy of stars, was first laid out by James W. Truran in 1981. He and subsequent astronomers showed that the pattern of heavy-element abundances in the earliest metal-poor stars matched that of the shape of the solar r -process curve, as if the s -process component were missing. This was consistent with the hypothesis that the s -process had not yet begun to enrich interstellar gas when these young stars missing the s -process abundances were born from that gas, for it requires about 100 million years of galactic history for the s -process to get started whereas the r -process can begin after two million years. These s -process–poor, r -process–rich stellar compositions must have been born earlier than any s -process, showing that the r -process emerges from quickly evolving massive stars that become supernovae and leave neutron-star remnants that can merge with another neutron star. The primary nature of the early r -process thereby derives from observed abundance spectra in old stars that had been born early, when the galactic metallicity was still small, but that nonetheless contain their complement of r -process nuclei.