When Babies Bang

A new study says the ruckus readies us for tool use


Of the many things babies do to prepare for adulthood, few are more, ahem, noticeable than banging. Put a Matchbox car in the sticky grasp of a six-month-old and you’ve got a one-man band unhinged enough to open for Slayer.

Babies have good reasons to want to bang on stuff. There’s a whole world out there, with sounds and textures and physical laws to explore. But what if an infantile proclivity for pounding is what led our distant ancestors to use rocks to crack open tough nuts? What if this impulse allows us as adults to successfully stake down a tent?

This is the argument laid out by Tulane researchers Björn Kahrs, Wendy Jung, and Jeffrey Lockman in a recent study in the journal Child Development. The researchers recruited 20 infants ranging in age from six months to 15 months and covered their arms and chests with reflective markers that could be detected by high-speed motion-tracking cameras. Then the hammering of mallets on tabletops commenced.

When the researchers plotted the trajectories of the babies’ bangs, they found that with age the movements grew smaller, straighter, slower, and more consistent from one strike to the next. In other words, the babies seem to converge, with time and practice, upon a controlled and efficient way of pounding—optimal, the researchers point out, for wielding a tool.

Given that tool use across the animal kingdom is commonly seen as a hallmark of intelligence, the implications are intriguing. After all, we are the smartest, best tool-wielders around.  But the use of very simple tools like hammers may have emerged not from a eureka moment involving an abstract understanding of the steps involved in achieving a goal, but rather gradually, from the exploratory behaviors we—and other simple tool-wielding species such as capuchins—are inclined to engage in anyway.

Like all theories of development, whether measured across months or centuries, plenty of chicken-and-egg questions remain. For one, was it the acquisition of exploratory banging that spurred on tool use, or did the benefits of tool use encourage exploratory banging via natural selection?

Probably more the latter, Kahrs tells me. But he’s quick to point out that both chicken and egg had a role to play. As far as we know, most monkeys are poor observational learners, meaning a baby capuchin is unlikely to figure out how to crack a nut just from watching her older family members. Nor is she likely to receive direct instruction. “Thus,” he says, “engaging in a lot of exploratory banging might have been, and still is, crucial to developing the skills necessary for nut-cracking”—which is, of course, what gives the skilled bangers that evolutionary advantage in the first place.

Another conundrum: if simple tool use arose not from insight but from repetitive, exploratory behaviors, why don’t more animals—frogs or hamsters or zebras—use tools? “One very limiting factor in tool use,” Kahrs explains, “appears to be the ability for fine motor manipulation. … This alone, I believe, prevents many animals (especially quadrupeds) from becoming tool users. Of those species who would have the necessary dexterity, I think research is showing that a fair number do show some rudimentary forms of tool use.”

To some extent, says Kahrs, intelligence still matters. Being smart enough to notice systematic relationships between sets of objects—like which rocks are effective against which surfaces—probably precedes even simple tool use. But a full understanding of the means by which a tool accomplishes a task? That—at least according to one interpretation—may only be required to build more complex tools: a stone-tipped spear, say, or the Internet.

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Jessica Love holds a doctorate in cognitive psychology and edits Kellogg Insight at Northwestern University’s Kellogg School of Management.


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