Human life histories

Reconstructions of the life histories of individual humans are a cornerstone of our understanding of the evolution of past populations, as single individuals are the driving force for changes at the population level. Beyond written records, biomineralized and keratinous tissues that preserve well post-mortem such as teeth, bones and hair represent the key archives of past life histories, especially those that grow appositionally such as dental enamel, thus preserving time-series information. Using the various elemental and isotopic proxies of mobility, diet or pollution, both established and novel ones, increasingly detailed life histories are being extracted from such archives, in no small part thanks to the methodological advances of the last ∼20 years, aimed at increasing the achievable spatial, i.e., temporal, resolution. Equally, these techniques facilitate an evaluation of the preservation of in vivo biogeochemical signals in bioapatite up to millions of years old, and the extraction of such signals even from partially preserved fossils. These advances simultaneously consume ever less sample and thus open up access to rare specimens. Successful recent applications have reconstructed weaning in Neanderthals vs. Modern Humans in the European Upper Paleolithic, seasonally-resolved dietary changes in South African Australopithecines or Indonesian Homo erectus and many more Meso-/Neolithic and younger reconstructions of past life histories. Future developments will include increased applications of novel dietary proxies such as Zn isotopes, Li/Ca, Li isotopes and δ15N from enamel proteins that will increasingly also include proteomic analysis such as gender identification. Increasingly, the identification of seasonal growth domains via δ18O in human enamel (via SIMS) coupled with similarly-resolved Sr/Pb-isotopic compositions and elemental dietary proxies (via LA-(MC-)ICPMS) will reveal an ever more nuanced picture of our human past and will ensure that this field will continue to develop fast.