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.
“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 “cold-blooded cognition” and recent studies revealing that reptile brains are not as primitive as we imagined.
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 lab 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,” Wilkinson said. Moses performed 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.
Things became even more interesting when 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 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.
Anole lizards 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 tight-fitting 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.
Then 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.
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. 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, Wilkinson deposited a tortoise on one side of a wire fence and a piece of strawberry on the other. To get their snouts on the treat, the tortoises needed to take a long detour around the fence. Not one tortoise figured this out on its own. But when they watched a trained tortoise navigate around the fence, all the observers learned to follow suit.