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In 1985, three researchers on [br]a dolphin-studying expedition

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got a little bored.

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To lighten things up, one pretended[br]to be Poseidon

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by placing a seaweed garland on his head[br]and then throwing it into the ocean.

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Moments later, a dolphin surfaced[br]with the seaweed crowning her head.

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Sure, this could have been a coincidence,

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but it's also entirely possible that[br]the dolphin was mimicking the scientist.

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That's because dolphins are one[br]of the smartest animals species on Earth.

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So exactly how smart are they?

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Like whales and porpoises,

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dolphins belong to the group[br]of aquatic mammals

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known as cetaceans[br]who comprise 86 different species,

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and share a common link with ungulates,[br]or hoofed animals.

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Originally land mammals,

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the first cetaceans entered the water[br]about 55 million years ago

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as large predators with sharp teeth.

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Then, a shift in ocean temperatures[br]about 35 million years ago

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reduced the availability of prey.

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One group of cetaceans who survived[br]this distrubtion,

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the odontocetes, wound up smaller[br]with less sharp teeth,

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but also larger and more complex brains

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that allowed for complex [br]social relationships,

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as well as echolocation to navigate[br]and communicate.

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Jump ahead to the present,

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and modern dolphins' brains are so large[br]that they're encephalization quotient,

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their brain size compared to the average[br]for their body size,

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is second only to humans.

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Dolphins have evolved to survive

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through their ability to form [br]complex social networks

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that hunt, ward off rivals,[br]and raise offspring together.

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For example, one group of Florida dolphins

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practices a sophisticated form[br]of cooperation to hunt fish.

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A dolphin designated [br]as "the net-maker" kicks up mud

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while another gives the signal

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for the other dolphins to simultaneously[br]line up and catch the escaping fish.

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Achieving a goal like this requires[br]deliberate planning and cooperation,

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which in turn requires some form[br]of intentional communication.

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Dolphins pass down their communication[br]method and other skills

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from generation to generation.

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Different dolphin populations exhibit[br]variations in greetings,

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hunting strategies,[br]and other behaviors.

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This sort of cultural transmission[br]even extends to tool use.

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One group of bottlenose dolphins[br]off the Australian coast

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nicknamed The Dolphin Sponge Club,

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has learned how to cover their rostrums[br]with sponges when rooting in sharp corals,

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passing the knowledge [br]from mother to daughter.

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Dolphins have even demonstrated[br]language comprehension.

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When taught a language based on[br]whistles and hand gestures,

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they not only understood[br]what the signals meant,

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but that their order had meaning:

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the difference between [br]bringing the ball to the hoop

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and bringing the hoop to the ball.

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So they were able to process two[br]of the main elements of human language:

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symbols that stand [br]for objects and actions,

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and syntax that governs [br]how they are structured.

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Dolphins are also one of the few species[br]who pass the mirror test.

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By recognizing themselves in mirrors,[br]they indicate physical self-awareness,

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and research shows they can recognize[br]not just their bodies,

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but also their own thoughts,[br]a property called metacognition.

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In one study, [br]dolphins comparing two sounds

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could indicate a same, different,[br]or uncertain response.

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Just like humans,

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they indicated uncertainty[br]more often with difficult trials,

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suggesting they're aware [br]of what they know,

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and how confident they feel[br]about that knowledge.

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But some of the most amazing things[br]about dolphins

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are their senses of empathy, altruism,[br]and attachment.

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The habit of helping injured individuals[br]extends across the species barrier

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as evidenced by the many accounts

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of dolphins carrying humans[br]to the surface to breath.

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And like us, dolphins mourn their dead.

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When we consider all the evidence,

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we may wonder why humans still hunt[br]dolphins for meat,

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endangering them through fishing[br]and pollution,

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or imprison them to perform tricks.

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The ultimate question may not be[br]whether dolphins are intelligent

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and complex beings,

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but whether humans can empathize with them[br]enough to keep them safe and free.