Periodic Reporting for period 1 - BABY PACE (Biped and Autonomous: Bone microarchitecture of the Youngest, PAthological and Cultural Effects) Reporting period: 2020-10-01 to 2022-09-30 Summary of the context and overall objectives of the project The BABY PACE project (Biped and Autonomous: Bone microarchitecture of the Youngest, PAthological and Cultural Effects) aims to understand whether different cultural contexts, in both normal and pathological conditions of development, have an impact on the development of the trabecular and cortical bone during the acquisition of bipedal walking. The combination of hereditary (genetics, sex, immunity) and environmental factors (e.g. geographic characteristics – altitude, rural locations, sun exposure –, socio-economic status in which a child develops, pathogen load) condition the development of a human being (size, rhythms, etc.). The importance of the influence of these many factors varies from a phase of development to another. Infancy, the first years after birth, is more sensitive to the environment. Thus, children living similar socio-economic, dietary, environmental contexts, tend to be the same size even with different genetic potentials. Infancy is a determinant period during which milestones leading to individual autonomy are acquired: weaning, language, continence, bipedal walking. The latter is typically acquired between 9 and 18 months around the world and cultural variations can be considered as an environmental factor influencing both its acquisition and maturation. BABY PACE focus to assess the roles of different environmental factors (e.g. socio-economic status, behavior, lifestyle) on normal and pathological skeletal development in children.Cultural differences imply different social considerations of what a child is, as well as potentially providing insights into important social steps such as the age of beginning work, or transition to adulthood. Thus, the cultural definition of these milestones leads to variations in body, and so, in bone biomechanics. The cultural variations of the rhythm of the psychomotor development produce biomechanical differences. It is known since a long time that the bone microstructural organization responds to the variations in biomechanical constraints. Moreover, the bone microarchitecture is significantly more sensitive to environmental factors and may be more reflective of variation than the whole skeleton. As bioanthropologists only have access to skeletons to understand individual development in past populations, the analysis of bone microarchitecture is an innovative way of response.BABY PACE hypothesizes that differences in developmental trajectories between cultural groups should be highlighted by variations in bone properties, reflective of disparate growth rhythms. bone biology as a cultural marker is a pioneering approach that will permit for the first time an understanding of ontogeny and childhood in the past which could allow interpretations about the place of children within their society, and aspects of funerary practices in cemeteries for future studies bases on BABY PACE results. Bone microarchitecture is not only useful to bioarcheological questions but also to society and public health questions. More widely, historical sciences such as bioarcheology provide insights into the present and future. Thus, a good understanding of the factors influencing skeletal development will provide useful new data on the prevention of age-related bone loss in contemporary populations and many other public health issues. Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far Due to the Covid-19 pandemic, the BABY PACE project has been reorganized and started later than planned. Also, due to professional opportunities, it has been terminated before the scheduled end. Despite these two facts, the main objective remained the same and even if all the planned analyses could not be done entirely, the first results of BABY PACE showed that, in a normal context of development for children from a very homogeneous industrial population, variations in the trabecular bone microarchitecture parameters in both distal metaphyses of radii and femurs have been observed. With advancing age, the radius showed, first, a homogenous distribution of the trabecular bone elements; then, a more concentric pattern with a denser bone medially; and finally, a gradient of moderate values, higher posteriorly. Simultaneously in the femur, no differences between the medial and lateral sides were observed and the trabecular bone was more isotropic at the periphery. Then, trabecular bone parameters showed differences between lateral and medial sides. Finally, lateral, and medial sides presented a similar organization, with a more isotropic bone at the midline. These patterns of the trabecular bone microarchitecture variation may relate to acquisition and maturation of bipedal walking and the associated changes in loading as children transition through stages including pre-locomotion, crawling, and bipedalism. For the pathological context of development, we focused the BABY PACE project on a metabolic disease well known for the populations of the past but also a disease which is still a public health issue: Rickets. It is related in most cases to a severe vitamin D deficiency and mainly affects infants from 0.5 to 2 years old, period in which they are developing their locomotor abilities. In this specific context, the trabecular organization for the pathological individuals is similar to the one of younger individuals from the normal sample but reveal a pattern which may confirm a degraded trabecular network due to the decreased mineralization of the bone tissue and a delayed locomotor development in the pathological children. Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) As the BABY PACE project has been terminated earlier, an important quantity of data is still under analysis. We have a lot of expectations especially regarding the comparison between children from different cultures and also from fossils from other human species which could lead to important discussions on the evolution of the growth processes and life history strategies through the human evolution.