The patterning of barium in tooth enamel is shown to be a reliable marker of lactation in humans and macaques; furthermore, the study of a tooth from a Neanderthal child reveals the weaning process in this extinct species. Weaning is a critical time in the life of any mammal, particularly for humans, in which early weaning allows women to have more babies in a shorter period of time than would otherwise be possible. The development of early weaning, therefore, could have had a profound influence on the evolution and success of Homo sapiens. Until now it has not been possible to determine age of weaning from fossils with any accuracy, but here Manish Arora and colleagues show that the ratio of barium to calcium in tooth enamel is a reliable marker of lactation in humans and macaques. Barium rises during lactation and drops abruptly on weaning. The study of a tooth from a well-preserved Belgian Neanderthal reveals the duration of exclusive breastfeeding, the period of a mixed diet, and a remarkably early age at weaning of about 14 months. Early-life dietary transitions reflect fundamental aspects of primate evolution and are important determinants of health in contemporary human populations1,2. Weaning is critical to developmental and reproductive rates; early weaning can have detrimental health effects but enables shorter inter-birth intervals, which influences population growth3. Uncovering early-life dietary history in fossils is hampered by the absence of prospectively validated biomarkers that are not modified during fossilization4. Here we show that large dietary shifts in early life manifest as compositional variations in dental tissues. Teeth from human children and captive macaques, with prospectively recorded diet histories, demonstrate that barium (Ba) distributions accurately reflect dietary transitions from the introduction of mother’s milk through the weaning process. We also document dietary transitions in a Middle Palaeolithic juvenile Neanderthal, which shows a pattern of exclusive breastfeeding for seven months, followed by seven months of supplementation. After this point, Ba levels in enamel returned to baseline prenatal levels, indicating an abrupt cessation of breastfeeding at 1.2 years of age. Integration of Ba spatial distributions and histological mapping of tooth formation enables novel studies of the evolution of human life history, dietary ontogeny in wild primates, and human health investigations through accurate reconstructions of breastfeeding history.

Imaging of iron and dopamine by laser ablation-inductively coupled plasma-mass spectrometry reveals a risk index for parkinsonian neurodegeneration

Element response variations under different laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) operating conditions were investigated to identify important factors for selecting an internal standard (IS) for quantitative elemental bio-imaging. Analytes covering a range of atomic masses and first ionisation potentials (FIP) were selected to investigate the signal response variation with changes in laser spot diameter, mass bias and cell sampling position. In all cases, an IS improved experimental precision regardless of a close match in element mass or FIP but optimal analyte/IS combinations depended on the difference in masses of the analyte and IS. Particular attention was paid to ¹³C as this isotope is typically used as an IS in elemental bio-imaging applications. Despite its non-ideal IS characteristics (often different mass and FIP to many analytes), possibility of abundance sensitivity effects and poor signal-to-background ratio, ¹³C was a suitable IS candidate exhibiting a linear response with respect to the mass ablated, apparent independence from the high abundance of the adjacent ¹⁴N mass peak and effective analyte normalisation after background subtraction as long as the ¹³C signal from the sample was at least 6% of the gross signal.

Calibration with matrix-matched standards remains the most practical means for producing quantitative images of trace metal distribution in tissue sections by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). A general guide for producing matrix-matched standards for assay of trace metals in brain tissue is presented. Cortical tissue was taken from pooled sheep brains and spiked with varying approximate concentrations of standard solutions of Co, Cu, Fe, Mg, Mn, Sr, Se and Zn. The tissue was homogenised and the total analyte amount accurately determined by solution nebulisation ICP-MS. The analytical figures of merit for LA-ICP-MS imaging were determined from these tissue standards cryosectioned at 30 μm. Repeated 8-point calibration curves were reproducibly linear, with correlation coefficients ranging from 0.9874 (Mg) to 0.9991 (Sr). Limits of analysis were suitable for quantifying most analytes in a sample mouse brain, with the exception of Co and Se.