The composition of the diet of ancient humans is commonly estimated by measuring the δ¹³C and δ¹⁵N ratios of collagen extracted from human bone. Because bone has been subjected to diagenesis during burial it is possible that its isotopic composition has been altered. DeNiro (1985) showed that if collagen has an atomic C/N ratio outside the interval 2.9 to 3.6, then it may show aberrant isotopic values. Here we show that the theoretical ideal C/N ratio of human collagen is at the midpoint of that interval (3.243). We also note that most measured ratios lie very close to that value. Deviations from that value due either to alteration of collagen or admixture of contaminant organic molecules are likely to shift the δ values away from their initial values. Values of C/N higher than 3.243 are likely to be due to contamination with humic matter while lower values might be due to selective loss of amino acids.

古人类饮食的组成通常通过测量δ估计的¹³ C和δ ¹⁵从人体骨骼中提取的胶原蛋白的N比率。由于骨骼在埋葬过程中已发生成岩作用，因此其同位素组成可能已经改变。DeNiro（1985）表明，如果胶原的C / N原子比在2.9至3.6之间，那么它可能会显示出异常的同位素值。在这里，我们表明人胶原蛋白的理论理想C / N比处于该区间的中点（3.243）。我们还注意到，大多数测得的比率都非常接近该值。由于胶原蛋白的改变或污染物有机分子的混合而导致的与该值的偏离可能会使δ值偏离其初始值。高于3.243的C / N值可能是由于腐殖质的污染，而较低的C / N值则可能是由于氨基酸的选择性损失。