True (verus) Troglodytes? Is this a movie scene in which Thor goes into a dark cavern to encounter strange, otherworldly creatures and challenge them to lift his hammer? No, Pan troglodytes verus is a species of chimpanzee, a species that uses “hammers” to crack open Coula edulis nuts. Well, not “hammers” as you are thinking: Basically fallen branches of Coula edulis and other trees used as hammers. The chimps find a hard surface like an exposed root that serves as an anvil on which they put the nuts they want to crack. And like you, they make an estimate of their “hammer’s” weight in their first lift and strike. You make such estimates every time you lift an object. Once you lift an object, you store its heft and plan your future lifts accordingly.
So, how do you do that estimating? When you have experience with an object, say a real or movie prop hammer, you have already stored information about the effort and strategy you need to lift it. But before you lift, you look for clues that you can, of course, misread. Misreading is easy when something appears to be a solid object, but is, in fact, hollow. And misreading also occurs when the object appears to be made of one substance like a dense cast iron but turns out to be made of painted plastic. We’ve all experienced the two ends of this weight-lifting spectrum: “Wow! This is a lot heavier than it looks,” and “Oh! I expected it to be heavier than it is.”
Now imagine some devilish trick played on chimpanzees in Côte d’Ivoire by some researchers interested in seeing how the animals respond to “hammers” of identical appearance but of different densities. Here’s what Giulia Sirianni and others did. They cut two pieces of Coula edulis wood to equal length, but hollowed out one. Then, they filmed the chimpanzees picking up the “hammers” to strike nuts. Of course, the upward acceleration of the lifted hollow hammer was much faster on the first try because these forest-dwelling Thors didn’t know they were lifting a prop.*
Don’t worry; no animals were hurt in this experiment, but the nuts fared poorly. Funded by the Max Planck Institute for Evolutionary Anthropology at Leipzig, Sirianni and colleagues wanted to measure the lifting process and to see whether chimpanzees, like humans, “anticipate the weight of an object using long-term force profiles...[suggesting] that, similarly to humans, they use internal representations of weight to plan their lifting movements.”**
Okay, so what? Both chimpanzees and humans can be fooled by the appearance of an object. “Nothing new,” you think. Probably, a likely outcome for almost every “first lift.” So, let’s emerge from somewhat troglodytic thinking that both we and the chimps exhibit at times, thinking by which we fool ourselves into accepting appearance over substance.
You can look at how others (possibly not you) see the objects used by people around them. Expensive cars, for example. Big homes. Great jobs. All have appearances that might not, in fact, be what they seem to be. Judging by “first lift” can be misleading. Maybe after handling the objects—and the lives—of others, we might all come up with a different estimate of the strategy needed to do the lifting. Maybe after experiencing the objects—and lifestyles—of others, we might exclaim, “Wow! That’s heavier than it looks,” or “Oh! I expected it to be heavier than it is.”
* Sirianni, Giulia, Roman M. Wittig, Paolo Gratton, Roger Mudry, Axel Schüler, Chrostope Boesch. (2017) Do chimpanzees anticipate an object’s weight? A field experiment on the kinematics of hammer‐lifting movements in the nut‐cracking Taï chimpanzees. Animal Cognition https://doi.org/10.1007/s10071-017-1144-0 Published online: 01 December 2017
**Abstract and article: http://pubman.mpdl.mpg.de/pubman/item/escidoc:2506422:2/component/escidoc:2506421/Sirianni_Do-chimpanzees_AnimCog_2017.pdf