There's actually a lot of evidence in primates and other animals that they return favors.

Frans de Waal

Quotation #17462

About This Quote

“Moral Behavior in Animals.” TEDxPeachtree. Nov. 2011. Conference Presentation.

Source: "Moral Behavior in Animals." TEDxPeachtree. Nov. 2011. Conference Presentation. Additional Information: According to this quote by Frans de Waal, who studies primate social behavior, many animals display behaviors that we associate with morality, including reciprocity -- or helping out one another. The quote is from de Waal's 2011 TED Talk about evidence of morality in animals. To illustrate his point that animals demonstrate reciprocity toward one another, de Waal presents videos of this behavior in chimpanzees and elephants. Watch the full TED Talk here: Frans de Waal - Moral Behavior in Animals