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Published on April 16, 2008

 It's certainly a foolproof example of the way humans consider themselves the rule by which everything else should be measured, but when we use it, there's a sense that we don't make that kind of mistake anymore. Yet even today scientists are swayed by the notion that humans stand at the centre of the biological universe, especially when it comes to what we care about most: our minds.

For years, scientists believed that the parts of the human brain that supported complex thought and language had only recently evolved. The mental life of animals was treated as primitive and utterly distinct from ours. But an explosion in animal research is showing that many components of human thought are shared with other species.

Evidence shows that parrots can understand numbers, crows make tools, elephants and hyenas live in complex, rule-governed societies, and chimpanzees make sense of the world in many of the same ways we do. The implication is indisputable: Humans are not unique.

The irony of the cognitive comeuppance for our species is that it also holds the key to a groundbreaking understanding of ourselves.

When we examine the mental overlap between us and many other species, we can more cleanly pick apart what elements of thought are special to us, what elements are shared with a few other animals and what is common to many.

This also means that we can begin to map the trajectory of the mind's evolution through millions of years.

Not only does this deepen our understanding of our own species, it puts evolution in its rightful place - as the Big Idea that is the foundation for all other research.

In recent years, the intersect between humans and other animals has become most obvious with respect to language. We have long thought that the one unbreakable wall between us and them, was our linguistic ability - we have it and they don't. It took an army of linguists, neuroscientists, paleoanthropologists and geneticists to prove that this is not the case.

We now know that chimpanzees and bonobos (pygmy chimps) are capable of understanding and even creating simple sentences, and that they make rudimentary references to objects with their natural cries. A border collie in Germany named Rico is able to correctly select many objects when they are named, and will even apply new words to novel objects.

Even in the wild, monkeys use a rudimentary form of structure in their calls, combining two calls to create a new meaning.

Animals' ability with numbers has also attracted more scientific attention. In 1999, researchers at Columbia University announced that they had taught two rhesus monkeys to count to four using images of shapes on a computer screen.

More recently, researchers at the Cognitive Evolution Laboratory at Harvard have shown that monkeys, like children, grasp small numbers precisely and approximate large numbers. Alex, an African grey parrot studied by Irene Pepperberg at Brandeis, was not only able to identify by word 50 different objects, seven colours and five shapes, he also comprehended numbers under 10 (although, interestingly, he did not count sequentially).

It's old news by now that humans aren't the only animals that use tools, but each year brings more strange, wonderful stories of how good the other guys are at it.

It was long assumed that gorillas were the only great apes that didn't use tools, but two years ago in Africa, gorillas were observed using sticks to test the depth of water before they stepped into it. And how about Betty, a New Caledonian crow housed in the aviary at Oxford University? In 2001, a lab researcher filmed Betty to see whether she or her aviary mate, Abel, would choose a hooked tool over a straight one to get a tiny toy bucket with meat inside it out of a glass cylinder. In one of the first trials, Abel accidentally knocked the hook away. Betty quickly hopped up and took the remaining straight piece of wire - a material she'd never seen before - found a suitable place to wedge it, bent it into a fine-looking hook and used it to retrieve the bucket of food.

Some groups use a fishing technique to get termites with sticks, while chimpanzees in Guinea are the only ones that stand atop palm trees and repeatedly beat the centre of the tree crown with a branch to make a pulpy soup. Science has been clear for a long time that humans are merely a twig on the ape branch of the great tree of life, but now research that puts humans' mental life in context is starting to catch up.

Of course, these are early days, and researchers expect the road to be as rocky as it is exciting.

In a recent letter to Science magazine, Victoria Horner of the Living Links Centre in Atlanta suggested an experiment in which the situation is reversed and trained apes administer the test to human children.

"We doubt," she observed, "this would do the children's performance any good!" Horner's excellent point speaks not only to this experiment but to all of cognitive science. We will learn more about ourselves if we examine our weaknesses as well as our strengths - and in this, animals have much to teach us.

Christine Kenneally is a freelance journalist and author of "The First Word: The Search for the Origins of Language."

Copyright: The Washington Post