In 2007, a study at the University of Zurich (Burkart et al., 2007) looked at cooperative behavior among common marmosets (Callithrix jacchus). The study found that the animals spontaneously provided food to “nonreciprocating and genetically unrelated individuals, indicating that other-regarding preferences are not unique to humans.”
Eleven years later, a new University of Zurich study (Brügger et al., 2018) has added a twist: Apparently, the marmosets get even more generous when no one is watching. The researchers documented the willingness of adult common marmosets to share food (crickets) with younger members of their group. They found that in the presence of others, the adult shared a cricket with the immature marmoset 67 percent of the time. But, surprisingly, when the adult and youngster were alone, the sharing behavior jumped to 85 percent.
This “reverse audience” effect runs counter to more self-focused explanations of animal altruism. When giving gifts to gain social status or helping out to show you are a team player, an audience is generally required. And with kin selection (helping family members to propagate shared genes), audience shouldn’t matter at all. The authors say the results here “appear to reflect a genuine concern for the immatures’ well-being, which seems particularly strong when [the adults are] solely responsible for the immatures.”