Detecting Pregnancy and Lactation using Bone Collagen Nitrogen Isotopes: a 'Proof of Concept' study

我们吃的任何东西都会在我们的骨头里留下化学信号，这是我们吃过的东西的记录。考古学家可以利用过去人类骨骼中的这种信号来了解他们的饮食习惯。这种技术现在被广泛使用，而且在广泛的层面上是可靠的。然而，过去几年的工作表明，其他影响，包括气候等外部影响和生长或压力等内部影响，都能微妙地影响这些化学信号，即稳定同位素值。特别是，对一种稳定同位素值（氮同位素值）的潜在影响因素是妊娠和哺乳。怀孕和哺乳已被证明会影响现代女性人类和动物的头发氮同位素特征。发生这种情况的机制尚不完全清楚，但可能是妊娠/哺乳期氮代谢变化的结果。迄今为止，尚不清楚在哺乳动物毛发中观察到的由于怀孕和哺乳而引起的氮同位素变化是否可以在骨胶原中看到。头发记录了体内短期的同位素变化，而骨骼则反映了体内数年甚至数年的平均同位素组成。然而，确定妊娠和哺乳是否记录在骨胶原蛋白中是很重要的。据报道，在多个时期和世界各地的考古人群中，成年男性和女性骨胶原氮同位素值存在微小但显著的差异，如果观察到差异，女性总是低于男性。目前，这种差异通常被解释为饮食差异，要么是男性和女性获得食物资源的差异，要么是不同饮食地区之间移民的证据。然而，可能观察到的是生理而不是饮食——内源性而不是外源性。我们需要对已知生活史的个体进行对照同位素研究，以测试怀孕和哺乳是否会影响个体的骨胶原氮同位素值。我们将在现代马鹿身上测试我们的假设，使用一个种群，我们已经证明了毛发的氮同位素值受到怀孕/哺乳的影响。然后，我们可以考虑在考古人群中观察到的男性和女性骨胶原氮同位素值的大范围差异是否与怀孕/哺乳有关，而不是与饮食差异有关。

Everything that we consume leaves a chemical signal in our bones, which is a record of what we have eaten. Archaeologists can use this signal in the bones of past human populations to find out about their dietary habits. The technique is now widely used, and is reliable at the broad-brush level. However, work over the last few years has shown that other influences, both external such as climate and internal such as growth or stress, can subtly influence these chemical signals, known as stable isotopic values. In particular, one potential influencing factor on one type of stable isotopic value, the nitrogen isotopic value, is that of pregnancy and lactation. Pregnancy and lactation have been shown to influence hair nitrogen isotope signatures of modern female humans and animals. The mechanisms by which this happens are not fully understood, but it is possible that the effect results from changes in nitrogen metabolism during pregnancy/lactation. To date it is unknown whether the nitrogen isotope changes observed in mammalian hair due to pregnancy and lactation can be seen in bone collagen. Hair records short-term isotopic changes in the body, whereas bone reflects the body's average isotopic composition over several, possibly many, years. However, it is important to identify whether pregnancy and lactation is recorded in bone collagen. Small but significant differences between adult human male and female bone collagen nitrogen isotopic values have been reported in archaeological populations from multiple periods and worldwide locations, with females always lower than males if a difference is observed. At present, such differences are generally interpreted as dietary differences, either differential access to food resources for men and women, or evidence of migration between areas with different diets. However, it may be that what is observed is physiological rather than dietary - endogenous rather than exogenous. We require controlled isotopic studies on individuals with known life-histories to test whether or not pregnancy and lactation affect an individual's bone collagen nitrogen isotopic values. We will test our hypothesis on modern red deer, using a population in which we have already shown that hair nitrogen isotopic values are affected by pregnancy/lactation. We can then consider whether wide-scale observed differences between male and female bone collagen nitrogen isotopic values in archaeological human populations could relate to pregnancy/lactation rather than dietary differences.