Oops, the scientist dropped his clothespin. Not to worry — a wobbly toddler raced to help, eagerly handing it back.
The simple experiment shows the capacity for altruism emerges as early as 18 months of age.
Toddlers' endearing desire to help out actually signals fairly sophisticated brain development, and is a trait of interest to anthropologists trying to tease out the evolutionary roots of altruism and cooperation.
Psychology researcher Felix Warneken performed a series of ordinary tasks in front of toddlers, such as hanging towels with clothespins or stacking books. Sometimes he "struggled" with the tasks; sometimes he deliberately messed up.
Over and over, whether Warneken dropped clothespins or knocked over his books, each of 24 toddlers offered help within seconds — but only if he appeared to need it.
Video shows how one overall-clad baby glanced between Warneken's face and the dropped clothespin before quickly crawling over, grabbing the object, pushing up to his feet and eagerly handing back the pin.
Warneken never asked for the help and didn't even say "thank you," so as not to taint the research by training youngsters to expect praise if they helped. After all, altruism means helping with no expectation of anything in return.
And — this is key — the toddlers didn't bother to offer help when he deliberately pulled a book off the stack or threw a pin to the floor, Warneken, of Germany's Max Planck Institute of Evolutionary Anthropology, reports Thursday in the journal Science.
To be altruistic, babies must have the cognitive ability to understand other people's goals plus possess what Warneken calls "pro-social motivation," a desire to be part of their community.
"When those two things come together — they obviously do so at 18 months of age and maybe earlier — they are able to help," Warneken explained.
But babies aren't the whole story.
No other animal is as altruistic as humans are. We donate to charity, recycle for the environment, give up a prime subway seat to the elderly — tasks that seldom bring a tangible return beyond a sense of gratification.
Other animals are skilled at cooperating, too, but most often do so for a goal, such as banding together to chase down food or protect against predators.
But primate specialists offer numerous examples of apes, in particular, displaying more humanlike helpfulness, such as the gorilla who rescued a 3-year-old boy who fell into her zoo enclosure.
But observations don't explain what motivated the animals. So Warneken put a few of our closest relatives through a similar helpfulness study.
Would 3- and 4-year-old chimpanzees find and hand over objects that a familiar human "lost"? The chimps frequently did help out if all that was required was reaching for a dropped object — but not nearly as readily as the toddlers had helped, and not if the aid was more complicated, such as if it required reaching inside a box.
It's a creative study that shows chimps may display humanlike helpfulness when they can grasp the person's goal, University of California, Los Angeles, anthropologist Joan Silk wrote in an accompanying review. Just don't assume they help for the reasons of empathy that motivated the babies, she cautioned.