Humans may be considered the most intelligent animals on Earth, but other species are not far behind. Scientists measure animal intelligence by looking at an animal’s self-awareness, self-control, and memory, all of which influence how well a creature processes information and solves problems. Judging an animal’s smarts is still a gray area, however. It’s pretty difficult to get a large number of wild animals together for a controlled behavioral experiment, and sometimes the tests scientists devise to judge a species’ intelligence don’t jive with the way animals perceive things. But the species included here have consistently impressed us with their smarts.
Dolphins have the second-largest brain relative to body mass in the animal kingdom (humans have the biggest), which is thought to be partly responsible for the mammals’ highly developed intellect. Captive dolphins are taught tricks, have been trained to detect underwater explosives, and star in TV sitcoms. They can also recognize themselves in a mirror, a basic test of self-awareness that indicates intelligence. Wild dolphins have been observed using tools, hunting cooperatively, and communicating in a variety of squeaks, squawks, and whistles, all pointing to dolphins’ cognition.
In some Native American folklore, ravens are known as tricksters — a reputation that may stem from these birds’ intelligence. Ravens and their relatives in the family Corvidae, which include crows and jays, have the same brain-to-body-size ratio as apes, suggesting a high level of cognition. Ravens are known for their complex social behaviors, such as holding apparent grudges against people who cheat them (a sign of their memory) and enacting “funerals” over dead members of their species, from which they pick up social information. Corvids also understand cause and effect, plan for the future, and make and use tools, like fashioning sticks to help them extract food from tight spaces.
Jane Goodall’s observations of chimpanzees using blades of grass to tease tasty termites out of their mound revolutionized our views of animal intelligence. And since her discovery in 1960, chimps have shown that their cognitive abilities rank pretty close to our own. In addition to the grass, chimps create special tools from leaves, twigs, and tree branches for different tasks. They also throw rocks at trees, perhaps to communicate to other chimps across a large area, and crack open nuts against anvil-like stones. Recently, scientists observed wild chimpanzees applying squashed insects to wounds as a form of self-medication. In addition, chimps interact with complex vocalizations and gestures and have even learned to “speak” with trainers in rudimentary pictorial or sign languages.
Pigs’ intelligence hasn’t been studied as thoroughly as that of primates, rodents, and birds, but analyses suggest that their performance on some psychological tests is on par with dolphins. A 2009 study found that seven out of eight pigs could process reflections of objects in a mirror and use the information to find food hidden behind a wall. Pigs can discern objects based on different characteristics and remember their choices over time, which demonstrates long-term memory. They can also prioritize which memories are important, like how to access desired food when presented with different options. Anecdotally, pigs have appeared to show empathy for humans, such as when naturalist Sy Montgomery’s normally active 750-pound porker, Christopher Hogwood, became quiet and docile while Montgomery grieved the loss of loved ones.
What octopuses lack in exoskeletons, they make up for in brains. These eight-armed cephalopods not only have the biggest brain-to-body-size ratio among invertebrates, but they also have multiple brains — a central neurological organ and one “mini-brain” in each arm. Octopuses can perceive and react to information quickly — by suddenly changing their color and pattern to camouflage themselves, for example — which suggests superior cognitive abilities. They’re famous for getting into and out of tight spaces, unscrewing jar lids, manipulating objects to solve puzzles, stealing crabs out of fishermen’s traps, and even escaping their aquarium tanks. A 2010 study of eight giant Pacific octopuses found that they could even recognize individual people.
Elephants are famed for their excellent long-term memory, a key indicator of animal intelligence. They can also solve practical problems. In a famous 2010 study, Kandula the Asian elephant figured out how to reach food on a high branch by pushing objects, like a large plastic cube, under the food and then using the cube as a step stool. Another well-known experiment found that elephants can grasp the need for cooperation and alter their behavior to achieve a shared goal. Observations of elephant social groups over decades have revealed tight relationships between different elephant generations, in which ecological knowledge is transferred from matriarchs to younger individuals.