During our time on this planet, we humans haven’t lent a hand to just anyone. Instead, we have usually saved our solicitousness for our own kind. And although over millennia the boundaries separating “us” from “them” have widened—from only kith and kin to entire neighborhoods and nations—the tendency has stayed the same: We help our own. Yet a surprising new experiment shows just how easily this human bias can be transformed into altruism. “The connections between affiliation to the group and prosocial behavior are so fundamental that, even in infancy, a mere hint of affiliation is sufficient to increase helping,” write coauthors Harriet Over, a doctoral student in psychology at Cardiff University in Wales, and Malinda Carpenter, a senior scientist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. For the study, a research assistant first showed each 18- month-old infant one of four possible sets of eight photographs. The photographs in all four sets featured a common household object (e.g., a teapot, book, or shoe) in the foreground. But each set had a different cue—a prime—in its background: two dolls facing each other (the affiliation prime), two dolls facing apart, one doll alone, or an inanimate object.…