Dolphins are perhaps the most intelligent aquatic mammal on Earth. With their self-awareness and abilities to communicate, reason, express emotions, adapt, and perform altruistic acts, they have spread across every ocean and many freshwater rivers in the same way humans have populated every continent. The cognitive abilities of dolphins are exceptional. Below is a close examination of this mammal's brain size, structure and remarkable cognitive abilities.
I. Brain Size / Structure:
Dolphins have a large, folded brain with an exceptional intellectual capacity. As a result, they learn extremely quickly and possess the ability to produce creative responses.
Although their cerebral cortex is 40% larger than that of humans, it is shallower, resulting in a neocortical volume that is 80% of that of humans. Nonetheless, both possess comparative cerebral hemispheres and folding to process sensory information and stimuli.
The average bottlenose dolphin brain weighs 1.7 kg (.4 kg more than the average human brain). When comparing brain size to body size – the Encephalization Quotient (EQ), the average dolphin brain registers between 4 and 5 (second to the 7 EQ of the average human brain and significantly higher than the EQ of any other type of animal including the great apes). This indicates a close proximity to human cognitive abilities.
In comparison to humans and other land mammals, a dolphin's brain has five versus six layers in their neocortex, with no functional segregation. This likely permits humans to focus on greater detail and dolphins to process sensory information at greater speeds, which may be more critical in a 3-dimensional water-based environment with few distinguishable landmarks where sound travels 4-5 times faster than on land.
In addition, relative to brain size, a dolphin's brain has a significantly larger cerebellum than a human. This is likely since an aquatic environment places greater need on motor control. Furthermore, a dolphin's cerebellum is also larger due to the absence of functional specialization, since it is likely used for cognitive processing.
Unlike the human brain, a dolphin's brain includes a paralimbic lobe to enhance integrated information and emotional processing. It is likely that emotions play a greater role in a dolphin's life than a human life.
Dolphins generally sleep in a semi-alert state by closing one eye and resting one side of the brain at a time. They usually alternate, closing one eye for 5-10 minutes and then the other. Within a 24-hour period, dolphins generally rest each eye and each side of the brain between 3-4 hours.
This is necessary so that dolphins can keep a lookout for potential predators – usually large sharks and killer whales. Remarkably, many dolphins in captivity, having recognized the absence of potential predators, rest both sides of their brain simultaneously, sleeping with both eyes shut.
II. Social Setting:
Dolphins are exceptionally social animals, consistent with humans, great apes and other creatures displaying high levels of intelligence. They occupy home ranges and live in pods or schools known as fission-fusion societies based on subgroups of age and sex-related individuals with size varying dramatically from about 6 to up to several thousand. At times, when there is an abundance of food, pods can join with each other forming superpods.
Although membership in pods is flexible and fluid, members of a pod form strong bonds with each other. Some pods are long lasting while others are merely temporary associations of individuals formed for a common goal. Nevertheless, dolphins refuse to abandon injured or ill individuals, assisting them to stay afloat to breathe if necessary. In addition, mother dolphins are known to take loving care of their young while entire pods will risk their safety to protect a mother and her calf from harm.
Within these pods, dolphins maintain intricate social networks. Each dolphin has a few close associates and additional more casual relationships with others within the pod. Dolphins breathe together, hunt together, coordinate their movements to capture prey, and take turns ingesting such prey. In addition, dolphins frequently alert others when large amounts of prey are discovered enabling others to get more food while enhancing safety with their greater numbers since potential predators may be interested in the same food source. Dolphins work exceptionally well during times of danger.
Dolphins are among the few species known to teach their young survival skills and culture. Mother dolphins teach their young to hunt through playful-looking movements, pointing gestures, and repetition. When teaching a calf to hunt, mother dolphins consistently take 8 times longer to capture and ingest their prey – often capturing and releasing it so that their calves can learn through observation and repetition. This transfer of knowledge is called "theory of mind." 
In addition to learning to hunt, young dolphins undergo extensive training. They learn about the rules of the pod, are disciplined when they act inappropriately, are taught about collaboration and cooperation, and about the identities and personalities of each member. Furthermore, to assist with the tasks, mothers share responsibilities and often take turns watching over hyperactive calves.
Dolphins are also taught to communicate through sound imitation. At this time, dolphins are the only non-human mammal to display strong evidence of vocal mimicry, vocal learning,  and learning of body movements through imitation.
In May 2005, it was discovered that the Indo-Pacific Bottlenose Dolphin passed on cultural behavior by teaching their young to break off sponges and cover their snouts with them while foraging for food. At the same time, it was discovered that some male dolphins in Brazil taught their young to use weeds and sticks as part of their sexual rituals.
Like other creatures of higher intelligence, dolphins at times engage in acts of aggression using their teeth and snouts as weapons. These disputes likely arise over competition for mates. At times these acts are so intense that targeted dolphins leave the pod or unfortunate calves fall victim to infanticide.
While sexual acts between dolphins are usually brief, foreplay can be lengthy and sexual acts can be repeated many times in a short timespan. In addition, dolphins may engage in sexual activity for pleasure and among different species, producing hybrids. However, at times, sexual activity can be violent with male dolphins displaying aggression towards both females and other males.
Complex play is also an important part of a dolphin's life. Dolphins occasionally perform acrobatic tricks, play with seaweed and other food, produce bubble rings that they then observe and even bite, and play-fight among themselves. They also enjoy surfing waves and even interacting with boats and other creatures such as whales and humans.
III. Multi-modal Sensory Perception:
Dolphins primarily use four senses to perceive the world around them. These senses, used in simultaneity and conjunction with each other, are vision, echolocation, taste, and touch. Together they are used to integrate information from their surroundings. Such information is processed at high speeds. Yet despite the multi-modal nature of dolphins, it appears that they have no sense of smell.
Dolphins have acute vision both in and out of water. In addition, their eyes possess both rods and L-Cones enabling them to see in dim and bright light, and possibly colors within the red and green light spectrums. Dolphins, however, can not see blue coloring except under certain light conditions when both the rods and L-cones, which have a very low sensitivity for blue light, are active. However, with 7,000 times as many rods as the human eye, dolphins can see extremely well in dark conditions such as murky water.
In addition, dolphins can move their eyes in different directions at the same time. One eye can look to the side while the other looks up enabling them to have two fields of vision with a 300 ° panoramic view. These two fields of vision can also overlap.
Dolphins generally hear tones within the frequency range of .25 to 150 kHz versus the average human auditory range of .02 to 17 kHz. In echolocation (the ability to see with their ears, in which the dolphin receives sound waves in the form of nerve impulses that are interpreted into a visual depiction of the object), dolphins may emit up to 700 clicks per second at between 40 to 150 kHz to detect the size and location of an object hundreds of meters away. In fact, dolphin echolocation is so sensitive that it can detect a 3-inch steel ball from approximately 90 meters away. Echolocation is also valuable in detecting echo signatures of potential prey.
Dolphins possess the ability to taste and differentiate between salt, bitter, sweet, and sour. This can be useful for navigation (ocean currents may have distinct chemical traces), orientation, discovering food, locating other dolphins, reproduction, and even stress sensitivity.
Dolphins also are extremely sensitive to touch which can be useful in sensing water movement and utilizing it to their advantage. The reason dolphins have such acute touch is because unlike human skin that possesses an epidermal layer of dead cells, a dolphin's outer layer of skin is composed entirely of live cells.
IV. Shape Recognition:
Studies have shown that dolphins can match simple and complex shapes with precision. In an early study, dolphins were able to match a cube, pyramid, and rectangular prism with high accuracy based on vision and echolocation.
In another study, a dolphin's ability to match 16 pairs of complex shapes and designs was tested through vision, echolocation, and multi-modal (vision and echolocation used in conjunction with each other) perception. The results were astonishing. During this experiment, an 8 year-old female bottlenose dolphin, Ebele was able to match 94.6% of the pairs through echolocation to vision (detected the pairs which hidden in a box through echolocation and then matched them through vision with pairs suspended in the water ), 97.1% of the pairs through vision to echolocation (detected through vision pairs suspended in water and matched them with pairs hidden in boxes through echolocation) in a sample consisting of 384 trials. The results were even equally astonishing when Ebele's multi-modal skills were tested. When tested to match pairs projected over a television screen (for which echolocation can not be used) with pairs suspended in the water that allowed Ebele to use vision and echolocation simultaneously, she was able to identify 95.8% of the pairs in a sample consisting of 24 trials.
V. Mirror Self Recognition (MSR):
The ability to possess sentience or self-awareness to think about oneself in the physical and mental realms illustrates a complex level of abstract thinking that is rare among animals. Studies have shown that dolphins possess this self-awareness.
Studies have shown that dolphins can recognize themselves in a mirror and investigate their own bodies. They have also shown that dolphins are aware of their own behavior and body parts as well as their feelings of doubt when subjected to difficult memory tests.
During the MSR tests, dolphins proved that they possessed selective attention in that they could pay attention to themselves in a mirror and were aware that they were viewing themselves instead of another animal.
When dolphins were marked with non-toxic ink or water markers consisting of no ink, they immediately swam over to a mirror or the most reflective object (when a mirror was not present) to inspect themselves. Furthermore, when dolphins had been marked by non-toxic ink, they spent more time in front of the mirror, carefully examining the marking on their bodies.
With their self-awareness, dolphins can also form analogies between their bodies and those of another, even improvising when the body of another species looks nothing like their own body. For example, if a person raises a leg, a dolphin may raise its tail.
In another example of self-awareness as well as understanding of cause and effect, dolphins have been observed to splash water on people who have approached their tanks and then raise themselves out of the water to determine the response their actions had elicited.
Dolphins can also discern the difference between reality and television. When observing others being fed on television, they initially swam up to the TV to check for fish. Afterwards, upon realizing that televisions projected depictions of reality, dolphins swam to their feeding areas when they saw others being fed on television, in anticipation that they too were about to be fed.
VI. Language and Communication:
Being among the most vocal of animals, dolphins are capable of producing a broad range of sounds ranging from whistles (their primary means of communication), burst-pulsed sounds (primarily used to convey a dolphin's emotional state ranging from pleasure to distress), and clicks (primarily for echolocation).
From a very young age, dolphins learn to produce a signature whistle (likely their name) based on imitation of a mother's signature whistle. This signature whistle allows others to identify the individual. In addition, dolphins also learn to imitate another's signature whistle so that they can likely address other dolphins by name, a key component of any functional language. They often whistle and respond to whistles to let others know where they are. In addition, a mother and calf who become separated, whistle frequently to locate each other until they are reunited. It is also believed that dolphins use whistles to refer to prey and objects. However, the extent is not known.
At the same time, it is known that dolphins use pulsed yelps during courtship, pulsed squeaks when in danger, and a rapid series of buzzing clicks when angry or involved in a confrontation.
In addition, dolphins also use body language as a means of communicating. This body language ranges from arching their bodies, bubble blowing, swimming with joined pectoral fins, flexing, head movement, nuzzling, jaw clapping, and even ramming and head butting.
Sufficient evidence exists that dolphins communicate information about "what," "where," and "who" while there is no substantive evidence of them communicating about "when," "how" or "why."  Furthermore, studies have shown that dolphins communication like that of humans, is intentional, the core purpose of developed languages. This communication ranges from playful, excited chatter to more serious conversation, for which the depth and content is not fully understood. A vivid example of dolphins' intentional communication occurred in an aquarium in Hawaii. When a mother and her two-year-old calf were placed in separate tanks that were connected via audio link, both mother and calf were observed chirping at each other as they rapidly exchanged information over a telephone link.
In addition, studies have shown that dolphins are capable of understanding symbols and hand gestures (mainly from American Sign Language), can learn associations between symbols, sounds, and objects without specific reinforcement or direct intervention, and can classify relationships between events. In fact dolphins have proven to be as proficient as humans when it comes to comprehending constructed sentence structures with a strong understanding of syntax (knowledge that word order makes a difference and changes the meaning of a sentence, for example dolphins know they can not fetch a person and put him or her on a surfboard) and semantics (comprehension of words and symbols). In addition, experiments have shown that dolphins can also discern between numerical values. They can comprehend if two or three objects are available and can also determine with little effort if something is absent. For example when a dolphin is asked to retrieve a Frisbee in the water, it does so with little effort when such a Frisbee is present. However, when asked to place a Frisbee that is present in the water on a surfboard that is absent, dolphins have been shown to respond that they can not do so since the surfboard is not present.
Studies have shown that dolphins have excellent memory systems. This has been proven by dolphins' abilities to learn sentence structure and meaning, retain human vocabularies of approximately 40 words in which thousands of sentences can be constructed, to memorize objects seen (matching them against new pairings consisting of pairs and triplicates of objects) and sounds heard (ranging from high frequency to long duration and match them against lists of between two to six different types of sounds) and by their ability to learn specific behaviors that can result in either adverse or rewarding experiences.
However, despite their excellent memory systems, the core of cognitive learning, dolphins appear to have a short-term memory that is more acute than their long-term memory. They were able to identify objects seen and sounds heard with a higher accuracy based on recency of effect.
Dolphins utilize vocal sounds and swimming patterns to express emotions in lieu of facial expressions.
Dolphins are generally affectionate creatures that show emotions towards their own kind as well as other species. They show concern for ill or injured members of their pod, they fiercely protect a mother and her young from predators, mourn for deceased members, and show excitement and joy when reunited with long lost members for which they had developed a bond. In addition, dolphins have displayed the capacity to show fear and concern and been shown to possess not only emotions that last for a short duration but also moods that could last for longer durations.
Stories date back thousands of years about the altruistic, selfless nature of dolphins. Dolphins are not only altruistic towards their own kind but other species as well. Many examples of intra- and interspecies altruism exist. At times, dolphins have sounded an alert heard 10 kms away to call other dolphins to assist in saving a human being. This interspecies altruism is likely the result of a dolphin's strong emotional feelings, self-awareness, "theory of mind," consciousness, and perhaps even the existence of a conscience in that they could not bear to see a human being perish anymore than a person could bear to see a dolphin or cat or dog perish. As a result, they transpose feelings of anguish, hurt, and loneliness onto others producing the same feelings of compassion that humans have for another. In essence, dolphins possess an openness and caring for other species.
A dolphin reportedly saved Telemachus, the son of Odysseus when he fell into the sea and nearly drowned as was written by Homer (c. 850 BC). In gratitude, Odysseus placed the figure of a dolphin on his shield.
Roman scientist Plinius (AD23-AD79) wrote about a dolphin that befriended a little boy. The boy fed the dolphin each day. One day when the dolphin did not see the boy, it searched for him. Upon discovering that he had drowned, the dolphin pushed his body onto a beach, laid next to him and died. Roman mosaics also show men playing with dolphins.
In the 18th century, a pod of dolphins saved Vietnamese sailors after their boat was sunk by hostile invaders.
In 1996, Martin Richardson was saved from a shark attack in the Red Sea when pod of dolphins encircled him and created turbulence to scare away the shark. The dolphins did not leave until Mr. Richardson was rescued.
In 2004, a group of New Zealand lifeguards were saved by dolphins that had formed a protective ring around them. The dolphins maintained the ring for about 40 minutes until 3 m-long shark had left. The lifeguards then swam to shore.
In 2007 a pod of dolphins saved surfer Todd Endris from a great white shark that had attacked him.
In March 2008, a dolphin came to the rescue of two pygmy sperm whales, a mother whale and her calf that were stranded on a New Zealand beach upon hearing the whales' distress calls. The dolphin led the whales 200 m along the beach and safely out to sea. This was similar to a 1983 incident at Tokerau Beach, New Zealand when a pod of dolphins herded a group of between 76 to 80 pilot whales and guided them safely out to sea.
Dolphins have been known to support a sick member of their pod and to standby an injured or ill companion regardless of the danger to themselves. They also work cooperatively in groups, assist each other in obtaining a mate, and put themselves at risk to defend a mother and her calf.
Based on the exceptional cognitive abilities of dolphins, the existence of cognitive convergence (in which brains of separate species share remarkable abilities to process sensory information and input from their surroundings and to communicate and comprehend language), one can hope for the day when interspecies communication is possible so that all species may develop a greater understanding of the world, greater appreciation for each other, and most importantly collaborate for joint solutions to preserve our wonderful planet. When or if interspecies communication is made possible through technology (eg computer links – dolphins have already been proven to understand computer-generated bars and disks that symbolize words and phrases in sign language) and greater understanding, from what can we learn better about what it takes to and is like living in all the oceans of the world regardless of temperature, depth, and chemical content, and anecdotal evidence of marine world issues than dolphins?
 Dolphins and the evolution of teaching. World Science. 17 August 2008. 7 January 2009. Http://www.world-science.net/exclusives/080807_dolphin.htm
 Diana Reiss, Brenda McCowan and Lori Marino. Communicative and other cognitive characteristics of bottlenose dolphins . Trends in Cognitive Science. Vol. 1, No. 4. Elsevier Science, Ltd. July 1997. p. 2.
 Margaret Klinowska. Brains, Behaviour and Intelligence in Cetaceans ( Whales, Dolphins and Porpoises). 17 September 1994. 26 January 2009. Http://www.highnorth.no/library/myths/br-be-an.htm
Adam A. Pack and Louis M. Herman. Sensory integration in the bottlenosed dolphin: Immediate recognition of complex shapes across the senses of echolocation and vision. Journal of the Acoustical Society of America. Acoustical Society of America. 1 August 1995. pp. 726.729 to 730.