Mothers are the privileged and essential partners of early life development for a large variety of vertebrates and invertebrates. The variation in maternal care likely contributes to the adaptive modulation of offspring phenotypical development by influencing them during a stage of high environmental sensitivity and phenotypic plasticity. But why aren’t the mothers all the same in a given population, and how such variability influences development? My research investigates the causes of interindividual variation in maternal social and nutritional care, as well as the short- and long-term effects on offspring behavior, cognition, and health. I will share findings from my studies on birds, rodents, and mammals to introduce the project I am now developing on the common marmoset at CerCo.