Humans have no exclusive claim on intelligence. Across the animal kingdom, all sorts of creatures have performed impressive intellectual feats. A bonobo named Kanzi uses an array of symbols to communicate with humans. Chaser the border collie knows the English words for more than 1,000 objects. Crows make sophisticated tools, elephants recognize themselves in the mirror, and dolphins have a rudimentary number sense.
And reptiles? Well, at least they have their looks.
In the plethora of research over the past few decades on the cognitive capabilities of various species, lizards, turtles and snakes have been left in the back of the class. Few scientists bothered to peer into the reptile mind, and those who did were largely unimpressed.
“Reptiles don’t really have great press,” said Gordon M. Burghardt, a comparative psychologist at the University of Tennessee at Knoxville. “Certainly in the past, people didn’t really think too much of their intelligence. They were thought of as instinct machines.” But now that is beginning to change, thanks to a growing interest in “coldblooded cognition” and recent studies revealing that reptile brains are not as primitive as we imagined. The research could not only redeem reptiles but also shed new light on cognitive evolution.
Because reptiles, birds and mammals diverged so long ago, with a common ancestor that lived 280 million years ago, the emerging data suggest that certain sophisticated mental skills may be more ancient than had been assumed — or so adaptive that they evolved multiple times.
For evidence of reptilian intelligence, one need look no further than the maze, a time-honored laboratory test. Anna Wilkinson, a comparative psychologist at the University of Lincoln in England, tested a female red-footed tortoise named Moses in the radial arm maze, which has eight spokes radiating out from a central platform. Moses’ task was to “solve” the maze as efficiently as possible: to snatch a piece of strawberry from the end of each arm without returning to one she had already visited.
“That requires quite a memory load because you have to remember where you’ve been,” Dr. Wilkinson said.
Moses managed admirably, performing significantly better than if she had been choosing arms at random. Further investigation revealed that she was not using smell to find the treats. Instead, she seemed to be using external landmarks to navigate, just as mammals do.
Things became even more interesting when Dr. Wilkinson hung a black curtain around the maze, depriving Moses of the rich environmental cues that had surrounded her. The tortoise adopted a new navigational strategy, exploring the maze systematically by entering whatever arm was directly adjacent to the one she had just left. This approach is “an enormously great” way of solving the task, Dr. Wilkinson said, and a strategy rarely seen in mammals.
Navigational skills are important, but the research also hints at something even more impressive: behavioral flexibility, or the ability to alter one’s behavior as external circumstances change. This flexibility, which allows animals to take advantage of new environments or food sources, has been well documented in birds and primates, and scientists are now beginning to believe that it exists in reptiles, too.
Anole, a tropical lizard, have a very specific method of acquiring food, striking at moving prey from above. But Manuel S. Leal, a biologist at Duke University, created a situation in which this strategy simply would not work, hiding a tasty insect larva inside a small hole and covering the hole with a tightfitting blue cap.
Two of the six lizards he tested tried to extract the treat by attacking the blue disk from above, to no avail. But the other four puzzled out new approaches. Two lizards came at the disk sideways, using their mouths to bite and lift it, while the others used their snouts as levers to pry it off the baited well.
Then Dr. Leal increased the difficulty by hiding the larvae under a new cap, this one blue and yellow. He used the solid blue disk to cover an adjacent, empty well. In tests of four lizards, two recognized the switch and learned that getting the bait now required flipping the multicolored disk instead of the blue one.
Other studies have documented similar levels of flexibility and problem solving. Dr. Burghardt, for instance, presented monitor lizards with an utterly unfamiliar apparatus, a clear plastic tube with two hinged doors and several live mice inside. The lizards rapidly figured out how to rotate the tube and open the doors to capture the prey. “It really amazed us that they all solved the problem very quickly and then did much better the second time,” Dr. Burghardt said. “That’s a sign of real learning.”
So how did we miss this for so long? Scientists say that many early studies of reptile cognition, conducted in the 1950s and ’60s, had critical design flaws.
By using experiments originally designed for mammals, researchers may have been setting reptiles up for failure. For instance, scientists commonly use “aversive stimuli,” such as loud sounds and bright lights, to shape rodent behavior. But reptiles respond to many of these stimuli by freezing, thereby not performing.
Scientists may also have been asking reptiles to perform impossible tasks. Lizards do not use their legs to manipulate objects, Dr. Leal said, “so you cannot develop an experiment where you’re expecting them to unwrap a box, for example.”
What’s more, because they are coldblooded, reptiles are particularly sensitive to environmental conditions. Rats and mice can run a maze just fine in a 70-degree lab, but many reptilian species need a much warmer environment — with air temperatures in the mid-80s or 90s. “They seem to learn the quickest at body temperatures that are very uncomfortable for us,” Dr. Burghardt said.
Now that scientists have gotten better at designing experiments for reptiles, they are uncovering all kinds of surprising abilities. Some of the most intriguing work involves social learning. The conventional wisdom is that because reptiles are largely solitary, asocial creatures, they are incapable of learning through observation.
New research calls that assumption into question. In another study of red-footed tortoises, Dr. Wilkinson deposited a tortoise on one side of a wire fence and a piece of strawberry on the other, in sight but just out of reach. To get their snouts on the treat, the tortoises needed to take a long detour around the edge of the fence.
Not one tortoise figured this out on its own. (Unable to reach the reward, some of the animals simply decided to nap.) But when they watched a trained tortoise navigate around the fence, all the observers learned to follow suit.
Other studies of reptiles have turned up similar results, challenging the popular theory that social learning evolved as a byproduct of — and a special adaptation for — group living. Instead, Dr. Wilkinson said, social learning may be merely an outgrowth of an animal’s general ability to learn.
The field of reptile cognition is in its infancy, but it already suggests that “intelligence” may be more widely distributed through the animal kingdom than had been imagined. As Dr. Burghardt put it, “People are starting to take some of the tests that were developed for the ‘smart’ animals and adapting them to use with other species, and finding that the ‘smart’ animals may not be so special.”
Herp ID: Cherry Head Red-footed tortoise (Geochelone Carbonaria) © East Bay Vivarium