According to the Discovery magazine website, animal intelligence is a highly subjective topic that often sparks debate. Dolphins are repeatedly nominated as one of the most intelligent species on Earth.
These animals possess highly developed language abilities and can learn complex tricks for television performances.Dolphins have served in the US Navy, and some believe they can even detect tumors, though science has not yet supported it.
"They have their own culture, use tools, and have complex societies," says Lori Marino, a neuroscientist and director of the "Whale Sanctuary Project" organization who has studied dolphin brains and intelligence for 30 years. "These animals are very similar to us, whether in complex social structures, behavior patterns, or self-awareness."
Extraordinarily Large Brain Proportion
What makes some people believe dolphins are the second smartest creatures? It relates to the relative size of their brains.
The American Museum of Natural History in New York City states that the deep-diving whale may have the largest brain volume of all creatures on Earth, reaching up to 20 pounds (about 9 kilograms). However, these massive marine mammals require greater computational power to perform basic tasks like movement.
Hans Thewissen, a professor at Northeast Ohio Medical University who studies cetacean evolution, says that the ancestors of modern dolphins began evolving larger brains from the ancestors of all whales and dolphins during the Eocene period (ending about 33 million years ago). Another leap occurred about 27 million years ago in early dolphins, the ancestors of modern dolphins, porpoises, and baiji.
However, brain size alone doesn't represent intelligence. Thewissen believes that this leap in early dolphins and other cetaceans likely occurred partly when their ancestors developed the ability to use echolocation to hunt prey.
Self-Awareness Capabilities
Learning about dolphins sometimes requires understanding our own way of thinking.
"We've known they're intelligent for thousands of years," says Marino, adding that observations of their curiosity can be traced back at least to ancient Greece.
The first serious scientific attempt to evaluate dolphin intelligence was conducted by John Lilly in the 1950s and 1960s, who studied bottlenose dolphin vocalizations. Lilly's early work laid the foundation for studying dolphin brains and intelligence.
Marino says the trouble is that the questionable ethics of some of his experiments often overshadowed this work and led to a lack of serious study of dolphin intelligence for many years. Lilly was a counter-culture figure who experimented with hallucinogenic drugs. These experiments extended to his marine mammal research, and in an attempt to communicate with dolphins, he began injecting them with LSD.
Eventually, researchers began studying dolphin intelligence again. A 2001 study published by Marino showed that dolphins can recognize themselves in mirrors. She and colleagues marked different parts of dolphins' bodies and then observed how the dolphins looked at those specific locations in mirrors placed in their tanks. Only a few other animals, such as chimpanzees, demonstrate this type of self-awareness.
"This was the first time cetaceans were proven to have this ability, which was previously thought to be limited to humans and our close relatives," she says. "Most animals can't do this."
Understanding Human Language
Other studies show that dolphins can be taught to understand basic human-created symbols, even sentences like "put the ball in the hoop."
"They understand grammar," Marino says. "They know that 'put the hoop on the ball' is different from 'put the ball in the hoop.'" But the problem with many of these tests is that they were conducted in captive environments. Just as some people are obsessed with understanding dolphin intelligence, others strive to exploit this intelligence, whether in popular aquarium dolphin shows, television programs.
Captive environments don't truly reflect how dolphins evolved and developed. Studying dolphins through artificial tests in laboratories may not be the best reflection of how dolphins mentally exceed their natural conditions. Therefore, Marino has begun to move away from testing captive dolphins.
"Much of the very interesting work being done now is conducted in the wild," she says.
Although understanding their behavior in the wild is much more complex, researchers still find abundant intelligent behaviors among cetaceans.
Bottlenose dolphins along Western Australia's coast have been observed using sponges as tools to protect their snouts and can search for fish in the sand on the seabed. Some cetaceans use mud nets to surround fish, and dolphins in Brazil have learned to cooperate with fishermen in southern Brazil to catch fish.
Setting aside hallucinogenic experiments, field studies even show that some dolphins may have very human-like flaws. It's unclear whether this is intentional or habitual, but observations show dolphins will poke pufferfish, entering a trance-like poisoned state, possibly absorbing the powerful neurotoxins from the pufferfish.
