Blue-Footed Boobies

Abstract The blue-footed booby is a better model than any primate for understanding some aspects of human family behavior because it reproduces monogamously and both partners share the workload of raising highly dependent, contemporaneous offspring. The author’s studies of thousands of banded blue-foots on a Mexican island over four decades confirmed theoretical predictions of conflict between sibling chicks and between bonded partners. Daily bullying by senior chicks trains junior siblings into subordination, guaranteeing seniors’ feeding priority while sharing food with juniors. But if parents bring insufficient food for two, senior chicks kill their sibs. Despite suffering multiple stresses of subordination, younger siblings that survive develop into fully functional adults. Adult blue-foots evaluate the quality, age, and condition of potential partners, pair-bond monogamously for the season, and cooperate closely with their partners for 6 months to raise one to three offspring. The sibling relations and marital relations of contemporary, historical, and prehistorical humans are similar in many ways to the behavior of blue-footed boobies, implying that, faced by similar problems, the two species (or their ancestors) evolved similar solutions.