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Structure of Dolphin Brain and Comparison to Primates?

  1. Sep 7, 2012 #1
    Dolphins have larger brains than humans. So, why aren't they smarter than humans... or, are they? Are those sneaky Dolphins playing dumb? j/k

    It's my (very limited) understanding that the cortex is responsible for the higher levels of what we think of as intelligence. So, what's different between the Dolphin's cortex and the human's or even chimp's cortex? I think I remember reading that the human cortex has 5 layers. How many layers does the Dolphin's cortex have?

    And how "intelligent" are Dolphins anyways? Are they more intelligent than Chimps?
  2. jcsd
  3. Sep 7, 2012 #2
    Just because they have larger brains doesn't by itself mean that they are more intelligent than humans. Dolphins bodies are larger than human bodies. So their brains have a lot more nerve endings to process. A brain can't be devoting itself to analysis if it has to process the input of a lot of nerve endings. Even the ratio of brain mass to body mass is not a good predictor of intelligence since most of the nerve endings are near the surface of the body.
    A better predictor of intelligence would the ratio of brain mass to surface area. This ratio is proportional to the encephalization quotient (EQ). The EQ is the ratio of brain mass to a power law with a 2/3 exponent. Roughly, the EQ is proportional to the ratio between brain volume and skin area. In terms of EQ, the bottlenose dolphin is second to humans in intelligence. According to its EQ, the bottlenose dolphin may have an intelligence greater than chimpanzees but less than that of humans.
    Scientists usually us a scaling parameter called the encephalization quotient (EQ) to estimate intelligence. According to some models, the EQ should correlate with intelligence. However, this is at best an approximation. As you point out, the structure and organization of the brain is also important. However, I don’t know of any quantitative parameters to take into account structure of the brain. So all we have for quantitative discussion is the EQ.
    The brain of mammals to adult body mass as a power law with an exponent on or about 2/3. The ratio of actual brain mass to the mass predicted by this formula is referred to as the encephalization quotient (EQ). According to Table 1 in the following link:
    Humans have an EQ of about 7.6
    Bottlenose dolphins have an EQ of 4.14
    Chimpanzees have an EQ of about 2.3
    Dogs have an EQ of 1.2.

    Here are some links. The first one gave me the EQ's that I quoted.
    Encephalization quotient
    Encephalization Quotient (EQ), or encephalization level is a measure of relative brain size defined as the ratio between actual brain mass and predicted brain mass for an animal of a given size, which is hypothesized to be a rough estimate of the intelligence of the animal.

    The formula for the curve varies, but is usually given as Ew(brain) = 0.12w(body)2/3. As this formula is based on data from mammals, it should be applied to other animals with caution. For some of the other vertebrate classes the power of 3/4 rather than 2/3 is sometimes used, and for many groups of invertebrates the formula may give no meaningful results at all.

    Dolphins have the highest brain-to-body weight ratio of all cetaceans.”

    Here is another link. Note that there are many species of dolphin, some of whom have an EQ smaller than that of chimpanzees. However, the bottlenose dolphin has the highest EQ of any mammal other than human beings.
    “Cetacean intelligence
    The encephalization quotient varies widely between species. The Orca has an EQ of 2.57, the franciscana dolphin of 1.67, the Ganges River dolphin of 1.55, the bottlenose dolphin of 4.14, and the tucuxi dolphin of 4.56.[9] These are less than the human EQ of 7.44, but some are greater than that of chimpanzees at 2.49,…”
    Note that the franciscana dolphin and the Ganges River dolphin are hypothetically stupid compared to the bottlenose dolphin and us. Not all dolphins are the same!

    This contains an EQ chart for prehistoric humans. Note that Homo habilis has about the same EQ as a bottlenose dolphin. Most of our prehuman primate ancestors were less intelligent than bottlenose dolphin.
    The article claims that high EQ can only be maintained with a diet which includes lots of meat. So I guess that the bottlenose dolphin got so smart eating fish. Fish is really brain food!
    “Encephalization quotient is basically the ratio of brain size to expected brain size. Humans are strikingly ahead of other primates. Since studies have shown that the only organs which diminished in size as our brains got large were our digestive tracts the conclusion is obvious. Eating meat allowed humans to have a source of energy efficient enough to allow our guts to shrink and our brains to grow. Only meat allows this to happen due to it's efficient delivery system.”
  4. Sep 7, 2012 #3
    I don't think that Tursiops truncatus playing dumb. I suspect that humans are too dumb to completely understand Tursiops trunctus (i.e., bottlenose dolphin).
    Here is a bottlenose dolphin family that learned to use a tool.
    “In Shark Bay, wild bottlenose dolphins (Tursiops sp.) apparently use marine sponges as foraging tools. We demonstrate that genetic and ecological explanations for this behavior are inadequate; thus, “sponging” classifies as the first case of an existing material culture in a marine mammal species. Using mitochondrial DNA analyses, we show that sponging shows an almost exclusive vertical social transmission within a single matriline from mother to female offspring. Moreover, significant genetic relatedness among all adult spongers at the nuclear level indicates very recent coancestry, suggesting that all spongers are descendents of one recent “Sponging Eve.” Unlike in apes, tool use in this population is almost exclusively limited to a single matriline that is part of a large albeit open social network of frequently interacting individuals, adding a new dimension to charting cultural phenomena among animals.”

    “Scientists say dolphins should be treated as 'nonhuman persons' Dolphins have been declared the world’s second most intelligent creatures after humans, with scientists suggesting they are so bright that they should be treated as “non-human persons”. Studies into dolphin behaviour have highlighted how similar their communications are to those of humans and that they are brighter than chimpanzees. These have been backed up by anatomical research showing that dolphin brains have many key features associated with high intelligence.”

    Dolphins seem to have communications abilities that are analogous to the language capabilities of human beings. Some of it seems auditory. However, they also use touch and gestures. One of their favorite gestures is blowing bubbles!
    http://colinallen.dnsalias.org/Secure/TCA/herman-final.pdf [Broken]
    “Semantics and syntax are considered the core attributes of any human natural language (Pavio and Begg 1981). Our studies of language understanding have revealed dolphin capabilities for processing both semantic and syntactic information (Herman et al. 1984; Herman 1986; Herman and Uyeyama 1999). The primary syntactic device used in our language studies has been word order. The dolphin is capable of understanding that word order changes meaning. It can respond appropriately, for instance, to such semantic contrasts as surfboard person fetch (take the person to the surfboard) and person surfboard fetch (take the surfboard to the person). In these language studies, the dolphin demonstrated an implicit representation and understanding of the grammatical structure of the language.”

    http://ec.europa.eu/research/infoce...29_en.html&item=Science in society&artid=9833
    “By using high-definition audio recordings of the marine mammals, the research team was able to assess the sounds' architecture pictorially. British acoustics engineer John Stuart Reid and US dolphin researcher Jack Kassewitz, who led the project, said the imaged sounds are known as 'CymaGlyphs'. According to the researchers, CymaGlyphs should form the basis of the lexicon of dolphin language, as each dolphin 'picture word' is represented by a different pattern.”

    Dolphins may use different modalities then human beings for “language”. They may sometimes use bubbles for “words”.
    “Bubble Ring Play of Bottlenose Dolphins (Tursiops truncatus):Implications for Cognition”

    I want to compare Tursiops truncatus to another animal with a similar EQ. However, I can't find an extant animal with a similar EQ. Instead, I want to compare Tursiops truncatus with an extinct animal with a very close EQ. This extinct animal is our own ancestor, Homo habilis!
    Homo habilis may have been one of the first of our ancestors to use a complex language.
    “The present consensus of paleoneurological research on the external aspects of complex language suggests that the changes associated with speech began early in hominid evolution, beginning with Homo habilis. There is evidence for continuity in these neural developments from the earliest Pleistocene to the present, and no evidence to suggest any modern human autapomorphies.”

    Homo habilis had an EQ close to that of bottlenose dolphins. Homo habilis may have been the first of the human ancestors to learn the use of tools and complex language.
    “Homo habilis is thought to have mastered the Olduwan era (Lower Paleolithic) tool case which utilized stone flakes. These stone flakes were more advanced than any tools previously used, and gave H. habilis the edge it needed to prosper in hostile environments previously too formidable for primates. Whether H. habilis was the first hominid to master stone tool technology remains controversial, as Australopithecus garhi, dated to 2.6 million years ago, has been found along with stone tool implements at least 100,000 - 200,000 years older than H. habilis.”

    http://www.cliffsnotes.com/study_guide/Homo-Habilis.topicArticleId-8741,articleId-8646.html [Broken]
    “Fossils dating back about 2 million years have been found with brain capacities much larger than any Australopithecus xfossil. On the basis of brain size, these fossils are named Homo habilis. Homo habilis is regarded as the first human and the first species of the genus Homo. Homo habilis means “handy human.” Members of this species were apparently able to use tools, build shelters, and fashion protective clothing.“
    Last edited by a moderator: May 6, 2017
  5. Sep 7, 2012 #4


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    Here's an interesting set of analyses for assaying mammalian intelligence (including EQ):


    In general, Human, Dolphins, Chimps, and Elephants are the top 4, but elephants place second for the "complexity" measure (dolphins and chimps tie) and also for cortical neuron count, but elephants place 4th for the EQ measure.
  6. Sep 7, 2012 #5


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  7. Sep 7, 2012 #6
    The link makes a small mistake by omission concerning encephalization quotient (EQ). It refers to a plot of brain tissue versus size as being linear. If size means length, then this statement is misleading.
    A dolphin has a higher ratio of brain mass to body mass then human beings. By this measure, dolphins should be smarter. The EQs shown in the table would be wrong. However, the EQ is not that ratio.
    If the amount of brain tissue is plotted against surface area, there is roughly a linear relationship. There is another way to look at it. The EQ is roughly proportional to the amount of brain tissue divided by the amount of skin!
    One way to justify this definition of EQ is to imagine a simplified model of how thinking works. Suppose that every cell in the brain is used to analyze the sensory input of each nerve ending on the surface, one at a time. Obviously, the EQ would be proportional to the number of brain cells used to analyze the input from one nerve ending. Increasing intelligence means assigning more brain cells to a nerve ending.
    One can make a computer analogy. Suppose that one has a PC hooked up to a modem. Like a modem connects to the network, nerve cells connect to the outside world. One can choose either the hard drive or the RAM for the next analogy. The number of nerve cells in the brain is like the amount of memory in the PC>
    The number of nerve cells increases with the baud rate of the modem. The EQ would be proportional to the amount of memory (hard drive or RAM) divided by the baud rate of the modem. If this ratio is too small, more information is coming in than the PC can handle. Then the PC will lock out. So the EQ is really proportional to the speed a brain takes to analyze all the sensory data coming in.

    “Maybe we can do better by incorporating the encephalization quotient (EQ). When the amount of brain tissue in a series of animals is plotted against size, from mice to elephants, there is a roughly linear relationship.”

    See, this is incomplete. You have to define the animal size. Looking at the 2/3 power law, it is obvious that “size” here means “area of skin”.
  8. Sep 8, 2012 #7
    Complete layman here, but I'm of an opinion that we don't really know what intelligence is or how to measure it. But I tend to look at it from an evolutionary standpoint; I see that dolphins have evolved for fast movement and under/above-surface acrobatics (which humans, I would say, aren't naturally any good at), underwater vision and hearing (which are harder underwater) and... well, here my layman knowledge comes to an end. Well, echolocation. While, as I see it, we, humans, have been streamlining our senses practically only to sight and hearing, and our bodies for cooperation. What I'm getting at is that I think it would be more useful to identify specific parts of the brain common to both compared species, and compare them, rather than work with a broad brush.
  9. Sep 8, 2012 #8
    Wow, thanks for all these references. Never heard of EQ before, and it's all very interesting.

    But, EQ seems to measure total brain mass, and from what I understand, it's mostly just the cortex that's responsible for higher-level thoughts, and all that stuff in the middle takes care of all the involuntary functions. Furthermore, each successive cortex layer can be thought of as processing more abstract data. So, I'm guessing that the size of the cortex, and the number of layers is what has the most effect on intelligence. Of course, these assumptions may be completely wrong. I know little about biology, and most of what I do know, I just got from watching some of Jeff Hawkins talks on YouTube, LOL. Such as this older TED talk:

  10. Sep 8, 2012 #9
    My original posts were responding to the general statements that you made about brain size. You suspected that whales were intelligent because the brain of a whale was bigger than the human brain. However, you had not taken account of the size of the whale in a physically meaningful way. Therefore, I tried to take into account the size of the brain so that we can concentrate on the other details.
    A blue whale has a brain MUCH bigger than a human brain, and bigger than the brain of Tursiops truncatus. However, Big Blue doesn't seem to behave as "smart" as Tursiops truncatus.
    The encephalization quotient (EQ) is probably a good way to start the discussion precisely because it is not specific to any one structural feature of the brain. The EQ.does not characterize intelligence. However, probably provides a good idea of the maximum possible power of the brain in terms of computational power. It probably gives a good idea of the maximum possible speed of that brain, and not the total quality of the brain.
    The EQ has already shown itself useful by highlighting the differences between cetaceans. It shows that we should not expect the same capabilities for a river dolphin then for a bottlenose dolphin (Tursiops truncates). The bottlenose dolphin shows the most potential in terms of intelligence of any cetacean with regard to brain size. So now we can focus on the specifics of how the brain of Tursiops truncates works, and not worry too much about the baleen whales.

    This is a guess, but we should discuss it.
    The cortex is not responsible for all thought. The cortex receives information from the rest of the brain that is already processed. The cortex is made of gray matter, which means that it is mostly cell nuclei.
    High level abstractions do not characterize most thinking. Many human beings have difficulty with higher order abstractions, yet they considered smart. Broca's center is a part of the human cortex that handles language. However, language may not be handled by Broca's center in Tursiops truncatus.
    I think that one should start with a broad brush rather than specific points because cetaceans have an entirely different anatomy then humans. Because cetaceans are organized differently, the way they use their brains has to be different from the way humans use their brains. Therefore, there can’t be a one on one correspondence between the way cetaceans use their brain and the way humans use their brains. Even if dolphins were intelligent in the way humans are intelligent, the different sections of the brain would have to function differently in humans and cetaceans.
    The homology of the brains of different species can be important, but also misleading. Dolphins could have an intelligence that is fully analogous but not homologous to the intelligence of humans.
    Blind human beings often shift control of language to the visual sections of their brain. Here is a link on the blind.
    “A person who is born blind may be able to recruit the unused brain regions related to vision for language-related tasks, a new study has found.
    "This suggests that brain regions that didn't evolve for language can nevertheless participate in language processing," said lead researcher Marina Bedny of the Massachusetts Institute of Technology. "”

    Deaf people use more parts of their brain then the sign language deprived (speakies?).
    “In addition, native signers, hearing and deaf, displayed extensive activation of homologous areas within the right hemisphere, indicating that the specific processing
    requirements of the language also in part determine the organization of the language systems of the brain.

    This study highlights the presence of strong biases that render regions of the left hemisphere well suited to process a natural language independently of the form of the language, and reveals that the specific structural processing requirements of the language
    also in part determine the final form of the language systems of the brain.”

    You are right about at least one thing. I promise to get away from discussing things in terms of the EQ. I was using the EQ to draw a boundary around the problem, not as an answer to the problem.
  11. Sep 8, 2012 #10
    I'm sort of getting a little Eureka moment (or maybe de-Eureka). There are a lot of thoroughly developed broad-brush approaches, and as far as I can see none are especially useful: animal intelligence is really evaluated by performance, not by anatomy. So I can see anything useful in the anatomical way arising from getting down to details: comparing brain structures, homologous by both anatomy and by function. Then, maybe, (if brainscans in dolphins are possible) brains would be scanned during relevant activities, such as speech, and areas and volumes involved compared with analogous ones in humans. Speech is part of intelligence, so it would be a part of the answer to the question in the topic.

    (Excuse my sleepy conjectures.)
  12. Sep 8, 2012 #11
    The cortex is not a simple object devoted to abstract thought. However, studies of the entire cortex have been performed on the species in question. The size of the entire cortex of ceteceans is comparable to primates.
    “When the mammalian brain increases in size, not all parts increase at the same rate.[6] In particular, the larger the brain of a species, the greater the fraction taken up by the cortex. Thus, in the species with the largest brains, most of their volume is filled with cortex: this applies not only to humans, but also to animals such as dolphins, whales, or elephants.”
    So Tursiops has as much cortex as Homo do. However, this is the entire cortex.
    Much of what is called intelligence concerns the frontal cortex. The frontal cortex is the part of the brain that determines self control. It determines the “information filters” most of us need to retain our sanity. Ceteceans have less frontal cortex than primates. Thus, this is considered evidence that maybe Tursiops is not as intelligent as chimpanzees.
    However, the cetacean cortex also has several regions which primates do not have. The function of these regions are unknown. How does anyone know whether these regions are analogous to the frontal cortex of primates? Tursiops could be more intelligent than a chimpanzee if it has another way to “filter information”.
    Here is a link on the sections of the cortex. Note that the fine structure of the cortex is different from that of humans.
    http://www.emory.edu/LIVING_LINKS/pdf_attachments/Marino_convergence.pdf [Broken]
    “In contrast, the cetacean brain evinces no elaboration of the frontal region. In fact the diminutive frontal cortical region in cetacean brains has prompted some investigators to relabel the anterior region of the cetacean brain with the term ‘orbital’ lobe [Morgane et al., 1980]. This difference in the degree of frontal cortical elaboration between primates and cetaceans is a pivotal point around which the relevance of finding self-recognition in dolphins (discussed later) revolves.
    Furthermore, whereas the primate brain is patterned into three contiguous lobes: rhinic, limbic, and supralimbic, the cetacean brain is organized around three distinct concentric tiers of tissue that include the limbic and supralimbic but also an entirely unique paralimbic region, the function of which is largely unknown. The segregation of the limbic and supralimbic regions by an interposed paralimbic lobe is a radical departure from the typical terrestrial mammalian pattern of cortical evolution [Morgane et al., 1980].”
    Here is an article that points out that cetacean cortex has a different structure from the primate cortex.
    “With that said, despite the sophistication of their narratives and analyses of behavioral parallels across cetaceans and primates, the authors' weakness lies in their discussion and interpretation of dolphin neuroanatomy and brain size in chapter five. For example, the authors claim that the size difference between the brains of dolphins and those of other mammals is accounted for mostly by hypertrophied auditory structures. But this point has not been established. There is, in fact, a vast portion of the cetacean brain that remains undescribed. Until we come much closer to an accurate estimate of the portion of cortical mass that is devoted to auditory processing in cetaceans, the authors' assertion cannot be validated. The authors also state that dolphins possess a larger neocortex than that of any primate, including humans. The neocortex of many cetacean species is massive, and cortical grey matter is relatively thin but extremely extended with more gyrification and surface area per volume than the human brain. However, there are currently no accurate or reliable values for absolute neocortical volume in cetaceans. Therefore, the claim that the cetacean neocortex is “larger” than that of primates is not only somewhat vague but unsubstantiated.
    Perhaps most troubling, however, is the authors' claim on page 141 that dolphin brain organization is superficially similar to an ape's, with a human-like set of frontal lobes and temporal lobes containing a structure that resembles the human language center. This mistaken representation of the cetacean brain runs counter to the pivotal point that cetacean and primate brains are anatomically divergent yet, in many ways, functionally convergent. The visually striking distinctive morphologies of the cetacean brain and primate brain are due to differences in cranial evolution as well as in regional elaboration and cortical surface mapping. And these differences are mirrored at a deeper cytoarchitectural level [3]. This point has particular relevance with regard to the frontal lobes. While the primate frontal lobe is a highly expanded structure, the cetacean frontal lobe is not nearly as elaborated, and is so different in morphology and cytoarchitecture that some authors have re-named it the “orbital lobe” to distinguish it from the more familiar primate frontal lobe [4].”
    Tursiops could have evolved intelligence by convergence with human beings. Homology comparisons are useful, but not definitive. As you pointed out, this really comes down to behavior.
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