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We have determined for the first time the ``electronic'' specific heat coefficient \ensuremath{\gamma}(x,T) of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6+\mathit{x}}$ for 0.16\ensuremath{\le}x\ensuremath{\le}0.97 between 1.8 and 300 K. Weakly superconducting behavior between x=0.43 and 0.8 progresses rapidly to BCS-like superconducting and metallic normal state behavior for x\ensuremath{\ge}0.9. However, the continuous development of the entropy S(x,T) with x and T across the entire series suggests a progressive modification of the low energy spin spectrum with hole doping rather than a simple band model. Fermi statistics and k-space pairing are indicaed by the magnitude and T dependence of S(x,T).