A lifetime of birthdays. What is shown here is a lifetime’s worth of birthday parties from age 1 to age 80. What is remarkable is that we have the ability to remember any one of these celebrations, with the exception of those from the first few years of our lives. The absence of memories from this infantile period was originally termed infantile amnesia by Freud. Since that time, infantile amnesia has been studied by psychologists using a wide range of empirical approaches, and across cultures a near universal pattern emerges: As adults, we have essentially no memories from below the age of 3, and only ‘spotty’ memories for events from ages 3-7. In this review, we develop a new neurobiological account of infantile amnesia. We argue that high levels of neurogenesis in the hippocampus are incompatible with memory stability, since the addition of new neurons leads to extensive remodeling of hippocampal circuits and, consequently, a loss of information stored in those circuits. As neurogenesis levels are highest postnatally, but decline with age, this predicts that memories acquired during infancy should be rapidly forgotten, but those acquired during adulthood should be more stable. The review is published in Learning & Memory this month, and a pdf version is available here.