Life history theory suggests that inter-birth intervals (IBIs) depend on a trade-off between maternal investment in current and future offspring, influenced by the mother's energy and somatic maintenance. Normally, IBI aligns with maternal and infant body size, larger relative infant size leading to slower breeding. In contrast, humans have relatively shorter IBIs due to cooperative breeding, support from the social group. Some other species with cooperative behaviors also exhibit shorter IBIs, possibly aided by factors like meat-eating enabling early weaning around 2.5 million years ago in the Homo lineage. Series: "CARTA - Center for Academic Research and Training in Anthropogeny" [Humanities] [Science] [Show ID: 39276]