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Published online by Cambridge University Press: 19 July 2016
This contribution starts with a very brief updated report on our present knowledge concerning the primordial abundances of the lightest elements (D, 3He, 4He and 7Li). From this information it is claimed here that specific models of chemical evolution able to account for a thorough destruction of D during the galactic history should be involved to reconcile the ratios : η = ηB/ηγ (baryonic density relative to background photon density) predicted respectively from the primordial 4He (Y) abundance and from the primordial D (and 3He) abundance. Among different possibilities; it is shown that galactic evolution models implying variations of the role of star formation (SFR) are more successful for that goal than models implying bimodal star formation. From this analysis it is also argued that contrary to a common belief, a large D destruction rate over the galactic history implies very specific conditions concerning the chemical evolution of our galaxy.