This is an oversimplification, but it will work for this discussion. An animal’s phenotype is observed or measured, but the animal’s breeding value is what is of interest to the sheep breeder. Unfortunately, it is not possible to know the true genetic merit of an animal for a particular trait. Therefore, in order to make selection decisions, its breeding value must be estimated. The animal’s ow...

Animal societies composed of breeders and non-breeders present a challenge to evolutionary theory because it is not immediately apparent how natural selection can preserve the genes that underlie non-breeding strategies. The clownfish Amphiprion percula forms groups composed of a breeding pair and 0-4 non-breeders. Non-breeders gain neither present direct, nor present indirect benefits from the...