One of the main tenets of evolutionary biology is that organisms behave so as to maximize the number of genes that will be passed on to future generations. This leads to one of two effects: parental attention and altruistic behavior; or parents producing more offspring than they will likely raise. The latter instance further leads to acute competitions, frequently leading to deprivations and even death. This book details the theory, field experiments, and natural history of sibling rivalry across a broad sweep of animals and plants. The variety of information will appeal to both academics and a broad natural history readership. In fact, most readers will relate, having all been children and most siblings or parents.