Reading hominin life history in fossil bones and teeth: methods to test hypotheses regarding its evolution

Human life history is derived compared to that of our closest living relatives, the great apes. It has been suggested that these derived traits are causally related to aspects of our ecology, social behaviour and cognitive abilities. However, resolving this requires that we know the evolutionary trajectory of our distinctive pattern of growth, development, and reproduction. Here, we (i) outline these derived features and the theories that have been proposed for their evolution; (ii) highlight the major gaps in our knowledge related to adult life history (reproduction and post-reproductive lifespan) with a review of our current knowledge, which is mainly based on information extracted from fossil teeth and bones; and (iii) provide an overview of novel analytical methods that leverage the biology of these hard tissues, to generate new information regarding the evolution of some of our peculiar life-history traits, such as short interbirth intervals (high reproductive frequency) and a prolonged female post-reproductive lifespan. Our review of tissue biology and analytical methods focuses on two tissues that are formed continuously during the entire lifespan of the individual and can therefore act as recording structures of adult life: dental cementum and lamellar bone. We conclude by providing specific guidelines for future research to help resolve the following long-standing question in human evolution: how and when did we switch from independent breeding to cooperative breeding, with its high reproductive frequency? Answering this question is crucial for understanding the evolutionary interplay between reproductive physiology and cooperation as well as for understanding how reproductive division of labour might shape societal structure.