Cetacean intelligence is the overall intelligence and derived cognitive ability of aquatic mammals belonging in the infraorder Cetacea (cetaceans), including baleen whales, porpoises, and dolphins. In 2014, a study found for first time that the long-finned pilot whale has more neocortical neurons than any other mammal, including humans, examined to date.
Brain size was previously considered a major indicator of the intelligence of an animal. However, many other factors also affect intelligence, and recent discoveries concerning bird intelligence have called into question the influence of brain size. [1] Since most of the brain is used for maintaining bodily functions, greater ratios of brain to body mass may increase the amount of brain mass available for more complex cognitive tasks. [2] Allometric analysis indicates that in general, mammalian brain size scales at approximately the 2⁄3 or 3⁄4 exponent of body mass. [3] Comparison of actual brain size with the size expected from allometry provides an encephalization quotient (EQ) that can be used as a more accurate indicator of an animal's intelligence.
Spindle cells (neurons without extensive branching) have been discovered in the brains of the humpback whale, fin whale, sperm whale, orca, [15] [16] bottlenose dolphins, Risso's dolphins, and beluga whales. [17] Humans, great apes, and elephants, species all well known for their high intelligence, are the only others known to have spindle cells. [18] : 242 Spindle neurons appear to play a central role in the development of intelligent behavior. Such a discovery may suggest a convergent evolution of these species. [19]
Elephant brains also show a complexity similar to dolphin brains, and are also more convoluted than that of humans, [20] and with a cortex thicker than that of cetaceans. [21] It is generally agreed that the growth of the neocortex, both absolutely and relative to the rest of the brain, during human evolution, has been responsible for the evolution of human intelligence, however defined. While a complex neocortex usually indicates high intelligence, there are exceptions. For example, the echidna has a highly developed brain, yet is not widely considered very intelligent, [22] though preliminary investigations into their intelligence suggest that echidnas are capable of more advanced cognitive tasks than were previously assumed. [23]
In 2014, it was shown for the first time that a species of dolphin, the long-finned pilot whale, has more neocortical neurons than any mammal studied to date including humans. [24] Unlike terrestrial mammals, dolphin brains contain a paralimbic lobe, which may possibly be used for sensory processing. It has also been suggested that similar to humans, the paralimbic region of the brain is responsible for a dolphin's self-control, motivation, and emotions. [25] The dolphin is a voluntary breather, even during sleep, with the result that veterinary anaesthesia of dolphins would result in asphyxiation. [26] Ridgway reports that EEGs show alternating hemispheric asymmetry in slow waves during sleep, with occasional sleep-like waves from both hemispheres. [27] This result has been interpreted to mean that dolphins sleep only one hemisphere of their brain at a time, possibly to control their voluntary respiration system or to be vigilant for predators.
The dolphin's greater dependence on sound processing is evident in the structure of its brain: its neural area devoted to visual imaging is only about one-tenth that of the human brain, while the area devoted to acoustical imaging is about 10 times as large. [28] Sensory experiments suggest a great degree of cross-modal integration in the processing of shapes between echolocative and visual areas of the brain.
The evolution of encephalization in cetaceans is similar to that in primates. [29] Though the general trend in their evolutionary history increased brain mass, body mass, and encephalization quotient, a few lineages actually underwent decephalization, although the selective pressures that caused this are still under debate. [30] Among cetaceans, Odontoceti tend to have higher encephalization quotients than Mysticeti, which is at least partially due to the fact that Mysticeti have much larger body masses without a compensating increase in brain mass. [31] As far as which selective pressures drove the encephalization (or decephalization) of cetacean brains, current research espouses a few main theories. The most promising suggests that cetacean brain size and complexity increased to support complex social relations. [32] [31] [30] It could also have been driven by changes in diet, the emergence of echolocation, or an increase in territorial range. [31] [30]
Some research shows that dolphins, among other animals, understand concepts such as numerical continuity, though not necessarily counting. [33] Dolphins may be able to discriminate between numbers. [34]
Several researchers observing animals' ability to learn set formation tend to rank dolphins at about the level of elephants in intelligence, [35] and show that dolphins do not surpass other highly intelligent animals in problem solving. [36] A 1982 survey of other studies showed that in the learning of "set formation", dolphins rank highly, but not as high as some other animals. [37]
Dolphin group sizes vary quite dramatically. River dolphins usually congregate in fairly small groups from 6 to 12 in number or, in some species, singly or in pairs. The individuals in these small groups know and recognize one another. Other species such as the oceanic pantropical spotted dolphin, common dolphin and spinner dolphin travel in large groups of hundreds of individuals. It is unknown whether every member of the group is acquainted with every other. However, large packs can act as a single cohesive unit –observations show that if an unexpected disturbance, such as a shark approach, occurs from the flank or from beneath the group, the group moves in near-unison to avoid the threat. This means that the dolphins must be aware not only of their near neighbors but also of other individuals nearby – in a similar manner to which humans perform "audience waves". This is achieved by sight, and possibly also echolocation. One hypothesis proposed by Jerison (1986) is that members of a pod of dolphins are able to share echolocation results with each other to create a better understanding of their surroundings. [38]
Southern resident orcas in British Columbia, Canada, and Washington, United States, live in extended family groups. The basis of the southern resident orca social structure is the matriline, consisting of a matriarch and her descendants of all generations. A number of matrilines form a southern resident orca pod, which is ongoing and extremely stable in membership, and has its own dialect which is stable over time. A southern resident calf is born into the pod of their mother and remains in it for life. [39]
A cetacean dialect is a socially–determined vocal tradition. The complex vocal communication systems of orcas correspond with their large brains and complex social structure. [40] The three southern resident orca pods share some calls with one another, and also have unique calls. [41] Discussing the function of resident orca dialects, researchers John Ford, Graeme Ellis and Ken Balcomb wrote, "It may well be that dialects are used by the whales as acoustic indicators of group identity and membership, which might serve to preserve the integrity and cohesiveness of the social unit." [41] Resident orcas form closed societies with no emigration or dispersal of individuals, and no gene flow with other orca populations. [42] There is evidence that other species of dolphins may also have dialects. [43] [44]
In bottlenose dolphin studies by Wells in Sarasota, Florida, and Smolker in Shark Bay, Australia, females of a community are all linked either directly or through a mutual association in an overall social structure known as fission-fusion. Groups of the strongest association are known as "bands", and their composition can remain stable over years. There is some genetic evidence that band members may be related, but these bands are not necessarily limited to a single matrilineal line. There is no evidence that bands compete with each other. In the same research areas, as well as in Moray Firth, Scotland, males form strong associations of two to three individuals, with a coefficient of association between 70 and 100. These groups of males are known as "alliances", and members often display synchronous behaviors such as respiration, jumping, and breaching. Alliance composition is stable on the order of tens of years, and may provide a benefit for the acquisition of females for mating. The complex social strategies of marine mammals such as bottlenose dolphins, "provide interesting parallels" with the social strategies of elephants and chimpanzees. [45] : 519
Dolphins are known to engage in complex play behavior, which includes such things as producing stable underwater toroidal air-core vortex rings or "bubble rings". [46] There are two main methods of bubble ring production: rapid puffing of a burst of air into the water and allowing it to rise to the surface, forming a ring; or swimming repeatedly in a circle and then stopping to inject air into the helical vortex currents thus formed. The dolphin will often then examine its creation visually and with sonar. They also appear to enjoy biting the vortex-rings they have created, so that they burst into many separate normal bubbles and then rise quickly to the surface. [47] Certain whales are also known to produce bubble rings or bubble nets for the purpose of foraging. Many dolphin species also play by riding in waves, whether natural waves near the shoreline in a method akin to human "body-surfing", or within the waves induced by the bow of a moving boat in a behavior known as bow riding.
There have been instances in captivity of various species of dolphin and porpoise helping and interacting across species, including helping beached whales. [48] Dolphins have also been known to aid human swimmers in need, and in at least one instance a distressed dolphin approached human divers seeking assistance. [49]
Aside from having exhibited the ability to learn complex tricks, dolphins have also demonstrated the ability to produce creative responses. This was studied by Karen Pryor during the mid-1960s at Sea Life Park in Hawaii, and was published as The Creative Porpoise: Training for Novel Behavior in 1969. The two test subjects were two rough-toothed dolphins (Steno bredanensis), named Malia (a regular show performer at Sea Life Park) and Hou (a research subject at adjacent Oceanic Institute). The experiment tested when and whether the dolphins would identify that they were being rewarded (with fish) for originality in behavior and was very successful. However, since only two dolphins were involved in the experiment, the study is difficult to generalize.
Starting with the dolphin named Malia, the method of the experiment was to choose a particular behavior exhibited by her each day and reward each display of that behavior throughout the day's session. At the start of each new day Malia would present the prior day's behavior, but only when a new behavior was exhibited was a reward given. All behaviors exhibited were, at least for a time, known behaviors of dolphins. After approximately two weeks Malia apparently exhausted "normal" behaviors and began to repeat performances. This was not rewarded. [50]
According to Pryor, the dolphin became almost despondent. However, at the sixteenth session without novel behavior, the researchers were presented with a flip they had never seen before. This was reinforced. [50] As related by Pryor, after the new display: "instead of offering that again she offered a tail swipe we'd never seen; we reinforced that. She began offering us all kinds of behavior that we hadn't seen in such a mad flurry that finally we could hardly choose what to throw fish at". [50]
The second test subject, Hou, took thirty-three sessions to reach the same stage. On each occasion the experiment was stopped when the variability of dolphin behavior became too complex to make further positive reinforcement meaningful.
The same experiment was repeated with humans, and it took the volunteers about the same length of time to figure out what was being asked of them. After an initial period of frustration or anger, the humans realised they were being rewarded for novel behavior. In dolphins this realisation produced excitement and more and more novel behaviors –in humans it mostly just produced relief. [51]
Captive orcas have displayed responses indicating they get bored with activities. For instance, when Paul Spong worked with the orca Skana, he researched her visual skills. However, after performing favorably in the 72 trials per day, Skana suddenly began consistently getting every answer wrong. Spong concluded that a few fish were not enough motivation. He began playing music, which seemed to provide Skana with much more motivation. [52]
At the Institute for Marine Mammal Studies in Mississippi, it has also been observed that the resident dolphins seem to show an awareness of the future. The dolphins are trained to keep their own tank clean by retrieving rubbish and bringing it to a keeper, to be rewarded with a fish. However, one dolphin, named Kelly, has apparently learned a way to get more fish, by hoarding the rubbish under a rock at the bottom of the pool and bringing it up one small piece at a time. [51]
As of 1984 [update] , scientists have observed wild bottlenose dolphins in Shark Bay, Western Australia using a basic tool. When searching for food on the sea floor, many of these dolphins were seen tearing off pieces of sponge and wrapping them around their rostra, presumably to prevent abrasions and facilitate digging. [53]
Whales use a variety of sounds for their communication and sensation. [54] Odontocete (toothed whale) vocal production is classified in three categories: clicks, whistles, and pulsed calls:
| Vocalizations of Southern Alaskan Resident Orcas |
There is strong evidence that some specific whistles, called signature whistles, are used by dolphins to identify and/or call each other; dolphins have been observed emitting both other specimens' signature whistles, and their own. A unique signature whistle develops quite early in a dolphin's life, and it appears to be created in imitation of the signature whistle of the dolphin's mother. [60] Imitation of the signature whistle seems to occur only among the mother and its young, and among befriended adult males. [61]
Xitco reported the ability of dolphins to eavesdrop passively on the active echolocative inspection of an object by another dolphin. Herman calls this effect the "acoustic flashlight" hypothesis, and may be related to findings by both Herman and Xitco on the comprehension of variations on the pointing gesture, including human pointing, dolphin postural pointing, and human gaze, in the sense of a redirection of another individual's attention, an ability which may require theory of mind.[ citation needed ]
The environment where dolphins live makes experiments much more expensive and complicated than for many other species; additionally, the fact that cetaceans can emit and hear sounds (which are believed to be their main means of communication) in a range of frequencies much wider than humans can means that sophisticated equipment, which was scarcely available in the past, is needed to record and analyse them. For example, clicks can contain significant energy in frequencies greater than 110 kHz (for comparison, it is unusual for a human to be able to hear sounds above 20 kHz), requiring that equipment have a sampling rates of at least 220 kHz; MHz-capable hardware is often used.
In addition to the acoustic communication channel, the visual modality is also significant. The contrasting pigmentation of the body may be used, for example with "flashes" of the hypopigmented ventral area of some species, as can the production of bubble streams during signature whistling. Also, much of the synchronous and cooperative behaviors, as described in the Behavior section of this entry, as well as cooperative foraging methods, likely are managed at least partly by visual means.
Experiments have shown that they can learn human sign language and can use whistles for 2-way human–animal communication. Phoenix and Akeakamai, bottlenose dolphins, understood individual words and basic sentences like "touch the frisbee with your tail and then jump over it". [62] Phoenix learned whistles, and Akeakamai learned sign language. Both dolphins understood the significance of the ordering of tasks in a sentence.
A study conducted by Jason Bruck of the University of Chicago showed that bottlenose dolphins can remember whistles of other dolphins they had lived with after 20 years of separation. Each dolphin has a unique whistle that functions like a name, allowing the marine mammals to keep close social bonds. The new research shows that dolphins have the longest memory yet known in any species other than humans. [63] [64]
Self-awareness, though not well defined scientifically, is believed to be the precursor to more advanced processes like meta-cognitive reasoning (thinking about thinking) that are typical of humans. Scientific research in this field has suggested that bottlenose dolphins, alongside elephants and great apes, possess self-awareness. [65]
The most widely used test for self-awareness in animals is the mirror test, developed by Gordon Gallup in the 1970s, in which a temporary dye is placed on an animal's body, and the animal is then presented with a mirror. [66]
In 1995, Marten and Psarakos used television to test dolphin self-awareness. [67] They showed dolphins real-time footage of themselves, recorded footage, and another dolphin. They concluded that their evidence suggested self-awareness rather than social behavior. While this particular study has not been repeated since then, dolphins have since passed the mirror test. [68] However, some researchers have argued that evidence for self-awareness has not been convincingly demonstrated. [69]
Cetacea is an infraorder of aquatic mammals belonging to the order Artiodactyla that includes whales, dolphins and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel themselves through the water with powerful up-and-down movement of their tail which ends in a paddle-like fluke, using their flipper-shaped forelimbs to maneuver.
A dolphin is an aquatic mammal in the clade Odontoceti. Dolphins belong to the families Delphinidae, Platanistidae, Iniidae, Pontoporiidae, and possibly extinct Lipotidae. There are 40 extant species named as dolphins.
The orca, or killer whale, is a toothed whale and the largest member of the oceanic dolphin family. It is the only extant species in the genus Orcinus and is recognizable by its black-and-white patterned body. A cosmopolitan species, they are found in diverse marine environments, from Arctic to Antarctic regions to tropical seas.
The bottlenose dolphin is a toothed whale in the genus Tursiops. They are common, cosmopolitan members of the family Delphinidae, the family of oceanic dolphins. Molecular studies show the genus contains three species: the common bottlenose dolphin, the Indo-Pacific bottlenose dolphin, and Tamanend's bottlenose dolphin. Others, like the Burrunan dolphin, may be alternately considered their own species or be subspecies of T. aduncus. Bottlenose dolphins inhabit warm and temperate seas worldwide, being found everywhere except for the Arctic and Antarctic Circle regions. Their name derives from the Latin tursio (dolphin) and truncatus for the truncated teeth.
Oceanic dolphins or Delphinidae are a widely distributed family of dolphins that live in the sea. Close to forty extant species are recognised. They include several big species whose common names contain "whale" rather than "dolphin", such as the Globicephalinae. Delphinidae is a family within the superfamily Delphinoidea, which also includes the porpoises (Phocoenidae) and the Monodontidae. River dolphins are relatives of the Delphinoidea.
The toothed whales are a clade of cetaceans that includes dolphins, porpoises, and all other whales with teeth, such as beaked whales and the sperm whales. 73 species of toothed whales are described. They are one of two living groups of cetaceans, the other being the baleen whales (Mysticeti), which have baleen instead of teeth. The two groups are thought to have diverged around 34 million years ago (mya).
The Indo-Pacific bottlenose dolphin is a species of bottlenose dolphin. This dolphin grows to 2.6 m (8.5 ft) long, and weighs up to 230 kg (510 lb). It lives in the waters around India, northern Australia, South China, the Red Sea, and the eastern coast of Africa. Its back is dark grey and its belly is lighter grey or nearly white with grey spots.
The common bottlenose dolphin or Atlantic bottlenose dolphin is one of three species of bottlenose dolphin in the genus Tursiops. The common bottlenose dolphin is a very familiar dolphin due to the wide exposure it receives in human care in marine parks and dolphinariums, and in movies and television programs. Common bottlenose dolphins inhabit temperate and tropical oceans throughout the world, absent only from polar waters. While formerly known simply as the bottlenose dolphin, this term is now applied to the genus Tursiops as a whole. As considerable genetic variation has been described within this species, even between neighboring populations, many experts think additional species may be recognized.
Cetacean surfacing behaviour is a grouping of movement types that cetaceans make at the water's surface in addition to breathing. Cetaceans have developed and use surface behaviours for many functions such as display, feeding and communication. All regularly observed members of the order Cetacea, including whales, dolphins and porpoises, show a range of surfacing behaviours.
Brain–body mass ratio, also known as the brain–body weight ratio, is the ratio of brain mass to body mass, which is hypothesized to be a rough estimate of the intelligence of an animal, although fairly inaccurate in many cases. A more complex measurement, encephalization quotient, takes into account allometric effects of widely divergent body sizes across several taxa. The raw brain-to-body mass ratio is however simpler to come by, and is still a useful tool for comparing encephalization within species or between fairly closely related species.
Von Economo neurons, also called spindle neurons, are a specific class of mammalian cortical neurons characterized by a large spindle-shaped soma gradually tapering into a single apical axon in one direction, with only a single dendrite facing opposite. Other cortical neurons tend to have many dendrites, and the bipolar-shaped morphology of von Economo neurons is unique here.
Encephalization quotient (EQ), encephalization level (EL), or just encephalization is a relative brain size measure that is defined as the ratio between observed and predicted brain mass for an animal of a given size, based on nonlinear regression on a range of reference species. It has been used as a proxy for intelligence and thus as a possible way of comparing the intelligence levels of different species. For this purpose, it is a more refined measurement than the raw brain-to-body mass ratio, as it takes into account allometric effects. Expressed as a formula, the relationship has been developed for mammals and may not yield relevant results when applied outside this group.
Human–animal communication is the communication observed between humans and other animals, ranging from non-verbal cues and vocalizations to the use of language.
The size of the brain is a frequent topic of study within the fields of anatomy, biological anthropology, animal science and evolution. Measuring brain size and cranial capacity is relevant both to humans and other animals, and can be done by weight or volume via MRI scans, by skull volume, or by neuroimaging intelligence testing.
Elephant cognition is animal cognition as present in elephants. Most contemporary ethologists view the elephant as one of the world's most intelligent animals. Elephants manifest a wide variety of behaviors, including those associated with grief, learning, mimicry, playing, altruism, tool use, compassion, cooperation, self-awareness, memory, and communication. Recent evidence suggests that elephants may understand pointing, the ability to nonverbally communicate an object by extending a finger, or equivalent.
Vocal learning is the ability to modify acoustic and syntactic sounds, acquire new sounds via imitation, and produce vocalizations. "Vocalizations" in this case refers only to sounds generated by the vocal organ as opposed to by the lips, teeth, and tongue, which require substantially less motor control. A rare trait, vocal learning is a critical substrate for spoken language and has only been detected in eight animal groups despite the wide array of vocalizing species; these include humans, bats, cetaceans, pinnipeds, elephants, and three distantly related bird groups including songbirds, parrots, and hummingbirds. Vocal learning is distinct from auditory learning, or the ability to form memories of sounds heard, a relatively common trait which is present in all vertebrates tested. For example, dogs can be trained to understand the word "sit" even though the human word is not in its innate auditory repertoire. However, the dog cannot imitate and produce the word "sit" itself as vocal learners can.
The evolution of the brain refers to the progressive development and complexity of neural structures over millions of years, resulting in the diverse range of brain sizes and functions observed across different species today, particularly in vertebrates.
The southern resident orcas, also known as the southern resident killer whales (SRKW), are the smallest of four communities of the exclusively fish-eating ecotype of orca in the northeast Pacific Ocean. The southern resident orcas form a closed society with no emigration or dispersal of individuals, and no gene flow with other orca populations. The fish-eating ecotype was historically given the name 'resident,' but other ecotypes named 'transient' and 'offshore' are also resident in the same area.
The evolution of cognition is the process by which life on Earth has gone from organisms with little to no cognitive function to a greatly varying display of cognitive function that we see in organisms today. Animal cognition is largely studied by observing behavior, which makes studying extinct species difficult. The definition of cognition varies by discipline; psychologists tend define cognition by human behaviors, while ethologists have widely varying definitions. Ethological definitions of cognition range from only considering cognition in animals to be behaviors exhibited in humans, while others consider anything action involving a nervous system to be cognitive.
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