Strictly speaking, humans are the smartest animals on Earth—at least according to human standards. We are adept at all the tasks we’ve established as intelligence indicators, and we have used our smarts to do everything from improving our quality of life as a species and building great societies to achieving scientific advancements such as sending people to the Moon.
But what about the millions of other animal species? How do we rate them? Measuring the intelligence of animals can be difficult because there are so many indicators, including the ability to learn new things, the ability to solve puzzles, the use of tools, and self-awareness. Determining the most intelligent animals can lead to debate—and some surprises.
Consider the octopus. At first glance, it might not appear to be very smart, yet studies have found that certain types of cephalopods possess great curiosity and problem-solving abilities. In one experiment, an octopus figured out how to unscrew a container lid to retrieve the tasty morsel inside. In another, an octopus learned to recognize human individuals, responding positively to a friendly person while ignoring a person who acted impersonally. The recognition of individuals is a sign of intelligence also shared by pigeons.
One might assume that chimpanzees—one of our closest genetic relatives—would rate highly on our intelligence scale, and they do. In a 2007 study, researchers gave adult chimps, adolescent chimps, and college students the same cognitive test, which involved remembering where nine numbers were located on a touchscreen monitor after seeing the numbers for less than a second. The adult chimpanzees and the college students scored about the same, but the adolescent chimps scored higher, remembering the number positions with far greater accuracy.
Goats, like octopuses, have proved to be adept at problem-solving, especially when food is their reward. In one test, goats had to use their teeth to pull a rope down, activating a lever they then had to lift with their mouths. A total of 9 out of 12 goats were able to figure out the contraption after four tries, and the majority still remembered how to work the device 10 months later.
Many animals are effective at using tools, including chimpanzees, which commonly use sticks to extract ants and termite larvae. Crows have demonstrated similar abilities, in one test proving smarter than human children. The test involved a cylinder containing water with a reward floating on top. The cylinder was too slender for a crow to reach into with its beak or for a child to insert a hand (children were not allowed to use their thumbs). Children under eight years old had a lot of difficulty figuring out the puzzle, but crows seemed to know instinctively that adding pebbles to the cylinder would gradually raise the water level until they could reach the reward.
Elephants, like many other animals, can learn a variety of complicated tasks, but it’s their self-awareness—the ability to recognize themselves in a mirror—that sets them apart on the intelligence scale. (Many other animals, such as dogs and cats, seem to believe their reflection is another animal and react accordingly.) Elephants are also highly social and compassionate, often working together to solve problems within their herd.
Other animals known for their intelligence include pigs, which can solve mazes and learn a symbolic language; rats, which can make decisions based on what they do and don’t know; and bottlenose dolphins, which possess the same degree of self-awareness as elephants.