Election Section

Handiwork Comes Easily to Remarkable Raccoons: By JOE EATON

Special to the Planet
Tuesday October 05, 2004

Although nature writers are supposed to have benign feelings about their (nonhuman, anyway) fellow creatures, I draw the line at raccoons: garbage-raiding, koi-eating thugs that make alarming noises in the dead of night. But to give the Devil his due, they’re good with their hands. Lacking opposable thumbs doesn’t seem to slow them down much. Scientists have claimed that raccoons far outrank their fellow carnivores in manual dexterity and are almost up there with the primates. 

The raccoon, in fact, caught the attention of a roboticist named Ian Walker about a decade ago. Walker was interested in nonhuman models for mechanical graspers, and analyzed the kinematics of the raccoon hand as a possible prototype. I don’t think this got much further, though, and Walker seems to have moved on to boneless manipulators like octopus tentacles and elephant trunks. 

Hands and brains work together, of course. It was established around the beginning of the 20th century that raccoons could quickly figure out how to open latches and other fasteners to get at food—not quite as quickly as rhesus monkeys, but faster than cats. And they could remember how they did it for up to a year without practice. 

The anatomy of the raccoons’ brain and nervous system, on which there’s a ton of literature, has tended to reinforce the idea that these critters have superior manual skills. In all of us mammals, there’s a chunk of the cerebral cortex—the somatosensory cortex—where the rest of the body is mapped; there’s a bit where sensory input from the face winds up, another for the forelimbs, and so on. Biologists had learned by the 1940s that some mammals had disproportionately large cortical regions for specialized body parts. In the pig, the area corresponding to the snout is larger than in other hoofed mammals. The spider monkey has extra room for input from its prehensile tail, which serves it as a fifth hand.  

Raccoons—no surprise—have an outsized cortical region corresponding to their forearms and hands. W. L. Welker and Sidney Seidenstein, neurophysiologists at the University of Wisconsin, reported in 1959 that 60 percent of the raccoon’s somatosensory cortex was devoted to the forelimbs, as opposed to 30 percent in the domestic cat and 20 percent in the dog. The hand-related proportion was even higher than in rhesus monkeys and chimpanzees. Welker and Seidenstein also found that raccoons’ auditory and visual cortical regions were relatively smaller than in dogs and cats, and speculated that their somatic cortex had “blossomed” at the expense of those areas. 

The Wisconsin study and others that followed made raccoons a favored lab animal for research on how the brain reconfigures itself after injury. Amputating a forefinger was found to cause a compensatory rewiring of the corresponding part of the cortex. (It turns out that the brain responds to less traumatic influences as well. In most right-hand-dominant musicians, the cortical region mapping to the right hand is enlarged. But for violinists, who finger with the left hand and bow with the right, it’s the left-hand region.) 

Meanwhile, other scientists found the skin of the raccoon’s fingers to be packed with specialized cells which were supersensitive touch receptors. Add that to the presumed superior dexterity, and you have an animal with enormous promise as a safecracker. 

It turns out, though, that the dexterity claim may have been oversold. 

Two neuroscientists at the University of Lethbridge in Alberta, Andrew Iwaniuk and Ian Whishaw, decided a few years ago to test the notion that raccoons were as skilled as primates by videotaping captives and analyzing their hand movements frame by frame. Their conclusion: the raccoon hand is a relatively crude instrument—not bad for a carnivore, but not in the primate league. And even other carnivores, including otters, mongooses, and the giant panda, may excel the raccoon in fine manipulation. (Giant pandas may be bamboo-eating vegans, but they’re carnivores by ancestry. As Stephen Jay Gould famously pointed out, they have “thumbs” which are actually modified wristbones.) The raccoons made little use of their individual fingers to grasp or manipulate food. 

What impressed Iwaniuk and Whishaw was that raccoons, unlike most carnivores, seemed to rely on their sense of touch alone to locate food items. Their filmed subjects often turned their heads away while fingering an object, and rarely sniffed an item before picking it up. Instead of a specialized manipulator, the hand of the raccoon appears to be a specialized tactile organ. 

That notion would be consistent with other studies that found raccoons did as well as humans in making blindfold distinctions between objects of the same shape but differing in size by as little as half a percent. The world a raccoon experiences must be very different from our own, with exquisite nuances of shape and texture. I have to wonder if their neural wiring enables them to somehow generate a visual image of what they’re touching, as appears to happen in readers of Braille. 

As to how this came about, Iwaniuk and Whishaw have an interesting speculation. The only other carnivore as touch-dependent as the raccoon is the marsh mongoose, which feeds on aquatic crustaceans. Common raccoons, of course, have a penchant for crayfish, and a tropical relative specializes in crabs. The evolution of the raccoon’s hand and brain may have been driven by grabbling in shallow water for food that could deliver a painful pinch if you grasped it wrong. 

Racoons, like them or loathe them, are remarkable creatures. They’re smart, tough, adaptable, and as likely as any species to outlast us. But their future seems unlikely to include tool use.