2.1. All Creatures Great and Small
Before we lavish attention on Homo sapiens, it's worth taking a look at the wayfinding skills of a few other species with which we share planet Earth. Their solutions to the challenges of orientation and navigation can illuminate our own. For example, have you ever wondered how ants find a feeding site and then return home? Lacking maps and street signs and cell phones, these tiny creatures regularly travel thousands of times their own body length to arrive at a pinpoint goal.
After decades of research, behavioral biologists have begun to figure out how. Studies show that ants use a combination of geocentric and egocentric techniques. Geocentric navigation (also called allocentric or exocentric) relies on external environmental cues such as landmarks and any available map information. Ants make intensive use of visual landmarks. In effect, ants take snapshots as they proceed from one location to another, and they're able to rely on those visual memories to retrace their routes. Before leaving home, an ant takes a visual snapshot of the panorama as seen from the nest. Upon return, the ant finds its nest by positioning itself so the current image of the environment matches the stored snapshot. If the image is smaller than the snapshot, the ant moves closer. If the image is larger, the ant moves away. Research shows that ants make use of multiple, successive snapshots to find their way along each foraging route.
However, this use of visual landmarks is not sufficient. Some landmarks move. Others become blocked from view. In many environments, memorable features are hard to find. The Sahara desert, home to the Cataglyphis ants, is particularly hostile to landmark navigation. And that's where egocentric navigation comes in. Egocentric navigation relies on self-awareness of distance and direction traveled and is independent of the immediate surroundings. Ants employ an egocentric strategy known as path integration to retrace their steps. This strategy is made possible by two remarkable senses. First, ants possess the biological equivalent of an odometer that tells them not just how many steps they have taken but the ground-level distance traveled during each segment of the journey. Second, ants possess a skylight compass that relies on the position of the sun as indicated by polarized light to compute direction. By combining knowledge of distance and direction, ants have a basic ability to retrace their steps independent of landmarks. Of course, these senses are imperfect, and errors can rapidly accumulate during the course of a trip. It's the sophisticated combination of strategies that allows for error correction and ultimate wayfinding success.
Sight. Hearing. Touch. Smell. Taste. We're often intrigued by the novel application of these five senses. Bats and whales and dolphins use echolocation to "hear" their way through low visibility environments. Salmon rely on a powerful sense of smell to sniff out routes as they navigate back to the upstream waters where they will breed. A "signature scent" characterized by the chemical composition of rocks and minerals leads them back to their place of birth. We're also impressed by unfamiliar wayfinding senses such as the polarized vision of ants and honeybees or the biomagnetism of sea turtles, lobsters, and newts. We can't help but speculate what it would be like to possess these remarkable capabilities. No wonder extra senses are a hallmark of our comic superheroes.
However, the story grows more interesting when we look beyond the senses to solve the puzzles of complex wayfinding behavior. Edward C. Tolman, a famous behavioral psychologist best known for his studies of learning in rats using mazes, provided new insight into the mysteries of wayfinding in his 1948 paper entitled "Cognitive Maps in Rats and Men."[*] The experiments began with rats exploring mazes in search of food. Through a process of trial and error, the rats learned to avoid deadends and increasingly select the best path to success. Over time, error rates fell and completion times dropped. At this point, the researchers changed the game by blocking some routes and opening up new ones. In response, the rats demonstrated an impressive ability to navigate the modified maze. Tolman concluded that rats construct a representation of their environment that allows them to take novel paths when the learned path is blocked. He called this representation a "cognitive map," a concept that has since been used to explain a wide variety of wayfinding behavior.
Most recently, marine biologists at the University of North Carolina have uncovered an even more sophisticated use of cognitive maps . We have long suspected that baby sea turtles have a built-in compass to guide them during their first open ocean migration. But, with the help of a massive cube-shaped coil system that can be used to reproduce the magnetic fields of various locations along the coast, these researchers have found that older turtles develop a "magnetic map " that includes their position and direction relative to home. Their magnetic sense combines with a natural mapping capability to form the biological equivalent of a global positioning system.
Finally, any account of animal wayfinding would be incomplete without the dance of the honeybee. Back in 350 B.C., the Greek philosopher and scientist, Aristotle, wrote in Historia Animalium (the History of Animals), "Each bee on her return is followed by three or four companions...how they do it has not yet been observed." A couple of thousand years later, we have a pretty good idea how they do it. We know that like ants, bees employ a combination of egocentric and geocentric strategies including a well-developed odometer, polarized vision, and landmark navigation. Bees also use color, scent, and even taste to supplement their nectar finding abilities. But what's really amazing about honeybees is their use of symbolic language to communicate the distance, direction, and quality of a food source. Individual honeybees describe the location of food through an elaborate "tail-wagging" dance. The message is amplified when multiple individuals point their fellow hive members to the same source. Not only do bees use language to support group wayfinding behavior. They also participate in collaborative filtering. Not bad for a bunch of insects!
As Edward O. Wilson, the father of sociobiology, suggests in The Future of Life, we can learn a lot from the millions of species surrounding us. In the realm of medicine alone, we humans stand to benefit tremendously. Nine of the 10 leading prescription drugs originated from living organisms, and we've hardly begun to tap the world's store of biodiversity. In fact, we have yet to find or name the majority of species. Roughly 1.8 million species have been discovered, but estimates of the true number of living species range from 3.6 million to 100 million. That's a pretty wide range. If we've barely begun counting the species, imagine how much we have to learn by studying their behavior.