The question of whether humans exhibit eusociality, a form of social organization observed in the animal kingdom, is a subject of scientific interest. Humanity’s intricate social structures, characterized by extensive cooperation and division of labor, invite comparison with species traditionally classified as eusocial. This article explores the biological definition of eusociality and examines how human societies align with, or diverge from, these criteria.
Defining Eusociality in the Animal Kingdom
Eusociality represents the highest level of social organization in animals, defined by specific biological criteria. First, eusocial species demonstrate cooperative care of young, meaning individuals beyond the biological parents contribute to raising offspring. Second, eusocial societies feature overlapping generations, where multiple adult generations coexist and contribute to the colony’s functioning. Third, a strict reproductive division of labor exists, with some individuals specializing in reproduction (often a queen or breeding pair) while others are sterile or less reproductive, performing tasks like foraging, defense, or brood care.
Eusociality is predominantly found among insects. Ant colonies, honeybee hives, and termite mounds exemplify these characteristics. In honeybees, a single queen reproduces, while thousands of sterile worker bees perform all other colony tasks, including foraging, nursing larvae, and defending the hive. Naked mole-rats, one of the few known eusocial mammals, live in underground colonies with a single breeding female and several breeding males, while other individuals are sterile and maintain the colony.
Eusocial Criteria and Human Societies
Applying eusociality’s biological criteria to human societies reveals similarities and differences. Humans engage in extensive cooperative childcare, or alloparenting, where individuals other than biological parents contribute to raising children. Grandparents, other relatives, and even unrelated individuals like teachers or babysitters regularly invest time and resources in childcare. This shared responsibility for offspring is a widespread feature across diverse human cultures.
Human societies also exhibit overlapping generations, particularly in multi-generational households where adults from different generations, such as parents, adult children, and grandparents, reside together. This living arrangement allows for intergenerational support, including shared caregiving responsibilities and mutual assistance.
However, the reproductive division of labor criterion presents a significant divergence for humans. While human societies feature a complex division of labor with specialized roles, this specialization does not typically involve biological sterility or a complete forfeiture of reproductive capacity for most individuals. Unlike eusocial insects where worker castes are often sterile, most human workers remain reproductively capable. Individuals may choose not to reproduce or have fewer offspring due to social or economic factors, but this is not a biological mandate enforced by a caste system.
The Ongoing Discussion: Are Humans Truly Eusocial?
The question of whether humans are eusocial remains a topic of debate among scientists. Proponents, such as biologist E.O. Wilson, suggest humans exhibit a “weak” or “functionally eusocial” form of social organization, drawing parallels between human cooperation and collective behaviors in ant colonies. They argue early human groups benefited from cooperation in raising young and foraging, leading to a “superorganism” effect where the group functions as a cohesive unit. This perspective emphasizes the success of human societies in various habitats, a trait shared with eusocial species.
Despite these arguments, the prevailing biological consensus holds that humans do not meet the strict definition of eusociality. The primary reason lies in the lack of a biological reproductive caste system. In species like ants or naked mole-rats, non-reproductive individuals are often physically different, sterile, and irreversibly committed to their roles, unable to transition to a reproductive function. Human societies, by contrast, do not biologically restrict the reproductive potential of most members. While social roles and economic circumstances can influence reproductive rates, they do not impose the inherent biological sterility that characterizes classic eusocial species.
Furthermore, genetic relatedness within human groups, while important for cooperative behaviors, is typically far lower than the extreme relatedness observed in many eusocial insect colonies, which often contributes to altruism through kin selection. Human cooperative behavior is influenced by cultural, social, and biological factors, rather than strict genetic programming for caste-based sterility. Therefore, while humans exhibit impressive levels of cooperation and social complexity, these traits do not align with all the specific biological criteria that define eusociality in the animal kingdom.