Science Watch

Sally Boysen, PhD, remembers the day in 1995 when renowned animal researcher Gordon Gallup, PhD, was taken aback by seeing one of her chimpanzees eating yogurt with a spoon. Here was a father of animal self-awareness research, who knew that chimps were master tool users, spellbound by the chimp’s simple act. Knowing animals are capable of tool use is one thing, but seeing it is quite another, Boysen says.

“He acted like she’d just recited the Gettysburg Address,” says Boysen, a cognitive psychologist at The Ohio State University.

Since the 1950s, a steady stream of research has shown that tool use isn’t unique to humans. Chimps use and modify tools to dig out termites from holes and smash tough nuts. Tool use has also been observed in captive baboons, gorillas and bonobos, wild and captive orangutans, and capuchin and macaque monkeys. Even nonprimates, including elephants, crows and woodpecker finches, create and use tools.

Still, it’s been unclear what these species have in common that allows them to manipulate objects in their environment to their advantage. But new research by psychologists is changing that. Psychologists have found similarities in brain structure and a common cognitive ability to represent abstract concepts, as well as an interesting evolutionary parallel between language and tool use in humans. Far from a mystifying and unique skill, these findings reveal tool use to be a quite common — albeit incredibly adaptable — strategy a number of animals have evolved to get the most out of their environments.

Word origin

As impressive as other animals’ tool-using abilities are, they pale in comparison to humans’ competence with highly complex technology. How did we get so tool proficient? Cognitive psychologist Thierry Chaminade, PhD, and paleoanthropologist and psychologist Dietrich Stout, PhD, believe the answer may be our ability to acquire language.

Chaminade, at the Mediterranean Institute for Cognitive Neuroscience in Marseilles, France, and Stout, at Emory University in Atlanta, published a meta-analysis last year in the Cambridge Archaeological Journal (Vol. 19. No. 1) arguing that in humans, language has developed hand-in-hand with the ability to use and create increasingly complex tools. Both skills require similar cognitive architecture and break down into structured sequences of behavior, they say.

There’s also overlap in at least one brain region, they add. The premotor cortex plays a big role in perceiving and making sense of language sounds, as well as telling the hands what to do when grasping, flexing and rotating. In a way, that overlap makes sense, they say. Both grasping and sound processing take discrete gestures — individual muscle movements of the fingers, wrist and arm; the individual sounds produced by the tongue, lips and palate — and merge them into something cohesive and meaningful, they say.

For hominids living 2.6 million years ago, “something meaningful” would be the stone tool, an early hallmark of progression toward complex tool-making.

So would making a stone tool have activated the premotor cortexes in our early ancestors? Chaminade and Stout tried to find that out through a modern-day recreation of a Stone Age task. They asked expert stone tool makers to create a stone hand axe by chipping away one stone with another during a PET scan. As they suspected, the researchers found a high degree of activation in the tool-makers’ premotor cortexes (Philosophical Transactions of the Royal Society of London Vol. 363, No. 1499).

As tools became an important aspect of human societies, evolution would have selected for expanded premotor cortexes and other brain regions responsible for tool use and creation. That, in turn, may have expanded the areas necessary for more complex language. And as language became an important trait in its own right, it too would be affected by evolutionary force, further accelerating expansion of these brain regions. Tool use reinforces language and vice versa, and evolution selects for both traits.

That scenario is wildly speculative, they admit, but the intriguing overlap in brain activation can’t be overlooked.

“In the end, we may come to see language and tool-making as alternate expressions of an underlying human capacity to make sense of the world in an increasingly complex way,” they say.

Chimps’ ‘extracted foraging’

Even though chimps can’t program a computer or build skyscrapers, new research finds they have increasingly impressive tool-using abilities. In one such study, Boysen has confirmed a behavior that chimp researchers have long suspected but never proven in a lab: Chimps not only know how to use tools, they can modify existing tools to suit different situations as they arise (Animal Cognition, Vol. 12, No. 1).

Boysen and her colleagues ran an experiment with nine chimps — five adults, two juveniles and two infants. The chimps were presented with one of two contraptions containing food, as well as pieces of PVC piping that they could manipulate into various tools. The first was a two-level box with a shelf separating the levels. By inserting a stick through a hole in the side of the box, the chimp could push a food reward off the shelf and down into the lower level, where he or she could pick it up and eat it. The second contraption was a flat plank, just out of reach, with a food reward on it and a dowel sticking up from it.

The PVC tool in its deconstructed state was simply a straight pipe with a T-joint at the ends, narrow enough to fit into the hole of the two-level box. By attaching dowels at the T-joint, the chimps could form a hook to catch the dowel and pull close the wooden plank. The researchers presented the chimps with one of the contraptions and the tool in either its constructed or deconstructed state, observed whether the chimps recognized the tool needed to be changed or kept the same, then repeated the process.

The adults and juveniles aced the test, adjusting the tool to its correct configuration nearly every time. The infants, though, were much less accurate, performing at or below chance when initially given a tool configuration that didn’t fit the contraption.

The fact that the adults and juveniles so effortlessly constructed and deconstructed the proper tool for the job seems to indicate a causal understanding of what a tool is and how it can be used, Boysen says. In fact, the chimps with their PVC pipes appear to be using the same cognitive resources you’d use to put together a bookshelf.

And those cognitive resources are likely an evolutionary extension of ordinary behavior, Boysen says.

“Whatever the species, in many respects, [tool use] is really just ‘extracted foraging,’” she says.

What’s extracted, she says, is a mental representation of what it is you’re foraging for. In this scenario, tool-using species have the ability to see their goals in the abstract, to separate the various causal relationships as between their bodies and their tools, the tool and the object they’re foraging for, and so on.

And, like in human infants, chimp infants need time and experience for their brains to develop enough to understand these mental representations. Both study their parents’ behaviors for years before they learn the ropes.

“Chimps and humans were the same species for 23 million years, so I would think there’s going to be some similarities there,” Boysen says.

Bird brains

That explanation accounts for our evolutionary cousins, but it doesn’t explain why birds can use tools. The hyacinth macaw, a parrot native to central and eastern South America, for example, uses wooden wedges to pop open nuts, says Douglas Wylie, PhD, a cognitive psychologist at the University of Alberta in Edmonton. New Caledonian crows fashion spears out of twigs, which they hold in their beaks to stab for grubs in trees.

So why can humans, chimps and certain birds use tools, while so many other species can’t? Wylie says part of the answer may lie in the cerebellum, home to motor control and motor learning, two cognitive skills necessary for tool use. Numerous studies over the last decade have looked to that brain region as the possible deciding factor in tool use, but they have yet to find any correlation between cerebellar volume and species that use tools. But it’s not just volume that counts, Wylie says. Brains also vary in the degree to which their cortexes fold. The more folding, the more connections among neurons, as well as increased surface area for the same amount of space.

For most vertebrates, the cerebellum consists of a thin sheet of neurons toward the rear of the brain, but in birds and mammals, the cerebellar cortex is more folded, scrunched and enlarged.

To determine whether crows, parrots and other tool-using birds might have more densely folded cerebellar cortexes than non-tool-using species, Wylie examined cortex data from 126 specimens representing 107 species. He found what he suspected was true — that crows and parrots topped the list of most-folded cerebellar cortexes among the species he studied, providing them with more connections and brain surface area in that region. Whether or not humans and the other great apes also have more folded cerebellar cortexes than other non-tool-using mammals remains to be studied, Wylie says. However, it is known that that their cerebella are more folded than at least the other primates.

To Wylie, that suggests a heavily folded cerebellar cortex “may be a common means of achieving proficient tool use,” he says.