Many animals exhibit smart behaviors. But do any of them show what humans would call "intelligence?" Some recently reported lines of research cautiously suggest that the answer is "yes."
Chimpanzees have surprised a research team by making wooden spears for hunting. It's the first known example of weaponmaking by a nonhuman.
Western scrub jays have shown future planning – rather than instinctive actions – in their food-caching behavior. Ravens have demonstrated logical thinking in solving a food-retrieval puzzle.
Such revelations are beginning to enable scientists to make the crucial distinction between genetically hard-wired behavior or trial-and-error learning and "intelligent" thinking.
Jill Pruetz of Iowa State University in Ames and Paco Bertolani at England's University of Cambridge reported the chimpanzee's surprising behavior earlier this month in the journal Current Biology. They observed it in southeastern Senegal.
Chimps have often been seen to use sticks to retrieve insects such as termites for food. This time, a chimp carefully sharpened a stick to make a spear. It then thrust the spear into a hole in a tree to skewer a bush baby – a small primate that chimps regularly eat. The researchers saw 22 instances of such spear hunting. Scientists know that chimps make tools, including stone tools. Now they are seen to be making weapons. The more closely chimps are studied, the more humanlike traits they display.
So, too, do some birds.
Reporting their work in Nature last month, Nicola Clayton and colleagues, also at Cambridge University, showed how western scrub jays plan for the future.
The food caches of these North American birds aren't random. Specific types of food are stored at specific locations to meet specific foreseeable needs. The scientists say their findings "suggest that the jays can spontaneously plan for tomorrow ... thereby challenging the idea that this is a uniquely human ability."
Bernd Heinrich at the University of Vermont in Burlington and Thomas Bugnyar at St. Andrews University in Scotland go further. They explain in the April issue of Scientific American why they think their studies "have finally offered some hard proof that ravens are indeed intelligent, in that they are able to use logic to solve problems."
The researchers set different ravens the task of retrieving food suspended at the end of a string that was tied to the bird's perch.
But instead of dashing about trying to grab the food in midair, a raven would sit and study the situation for a few minutes. Then it would quickly go through the logically correct sequence to retrieve the food efficiently. The steps involve pulling up a loop of string and putting a foot on it to hold it, then pulling up more string, and so forth. Soon the bird had pulled up the entire string and obtained the food.
In other tests, ravens showed that they could distinguish between individuals – both ravens and humans.
A raven could then assess whether or not another individual was likely to have observed where that raven had stored food. The raven then knew which other individuals knew enough about its food caches to be potential thieves.
Humans make such assessments all the time. Drs. Heinrich and Bugnyar note that "in this way, too, they [the ravens] are much like humans."