Eusociality represents the highest stage of animal social evolution, defined by three core characteristics: reproductive division of labor (with permanent/obligately sterile worker castes) , overlapping generations, and cooperative brood care. Some advanced lineages have further evolved morphologically differentiated castes (e.g., soldier ants, worker ants). This trait has evolved independently more than 20 times across the animal kingdom, spanning multiple phyla from flatworms to mammals. The ...