Which animal is the smartest?

Strictly speaking, humans are the most intelligent animals on Earth—at least by human standards. We excel at all the tasks we are assigned as intelligence indicators, and we use our intelligence to do everything from improving the quality of life for humans as a species and building great societies, to achieving scientific advancements like putting a man on the moon.

But what about the millions of other animal species? How do we evaluate them? Measuring an animal's intelligence can be difficult because there are many indicators, including the ability to learn new things, solve puzzles, tool use and self-awareness. Identifying the smartest animals may spark debate, but it can also lead to some surprises.

Consider the octopus. It might not look very bright at first glance, but research has found that certain types of cephalopods have great curiosity and problem-solving abilities. In one experiment, an octopus figured out how to unscrew the lid of a container to get out the delicious food inside. In another study, octopuses learned to recognize human individuals, reacting positively to friendly individuals while ignoring those who behaved inhumanely. Recognition of individuals is a sign of intelligence that pigeons also possess.

One might think that chimpanzees—one of our closest relatives—would rate highly on our intelligence scales, and they do. In a 2007 study, researchers gave adult chimpanzees, adolescent chimpanzees and college students the same cognitive test, which included remembering the location of nine numbers on a touchscreen display less than a second after seeing the numbers. . Adult chimpanzees and college students scored about the same, but adolescent chimpanzees scored higher and remembered the location of numbers with much greater accuracy.

It turns out that goats are just as good at problem solving as octopuses, especially when they're rewarded with food. In one test, goats had to pull down on a rope with their teeth, activate a lever, and then lift the lever with their mouths. After four attempts, nine out of 12 goats were able to figure out the device, and most still remembered how to use it 10 months later.

Many animals are skilled tool users, including chimpanzees, who often use sticks to extract ant and termite larvae. Crows have shown similar abilities, proving to be smarter than human children in one test. The test involves a cylinder filled with water with a reward floating on it. The cylinder is too slender for a crow to reach into with its beak and for a child to reach out (children are not allowed to use their thumbs). The puzzle would be difficult for children under eight to solve, but the crows seemed to know instinctively that adding pebbles to the cylinder would gradually raise the water level until the reward was reached.

Elephants, like many other animals, can learn a variety of complex tasks, but their self-awareness—the ability to recognize themselves in a mirror—sets them apart on an intellectual level. (Many other animals, such as dogs and cats, seem to think their reflection is another animal and react accordingly.) Elephants are also highly social and empathetic, often working together to solve problems within the herd .

Other animals known for their intelligence include pigs, which can solve mazes and learn symbolic languages; rats, which can make decisions based on what they know and don't know; and bottlenose dolphins, which have the same degree of self-awareness as elephants .

So determining which animal is "smartest" really depends on your criteria. Perhaps a more pressing question is: Are other animals judging our intelligence? If so, how do we stack?

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