Cetacean Intelligence

Dolphins
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Ranking mammalian intelligence is a tricky thing. Neuroanatomically speaking, the mammalian order Primates is most studied, with the most extensive research (of course) on humans and other great apes, both of the family Hominidae. Primates reign highest in animal intelligence rankings, with cetaceans and elephants following. Multiple factors contribute to deeming “intelligence”, including relative brain size and weight, number of cortical neurons, cortical complexity, and encephalization quotient (EQ).

What specifically about cetaceans ranks them so highly?

 Modern cetaceans have the largest mammalian brains in absolute size, and maintain the highest ratio of brain size to body size. Cetaceans also have a high EQ, which is a measure of relative brain size that roughly estimates the cognitive capacity of an animal. EQ also adjusts for something called cephalization factor that recognizes sheer brain size to body size is not necessarily reflective of intelligence, and therefore also incorporates observed complex behavior.

Studies suggest that ancient toothed cetaceans did not always have such a large relative brain size, but that this occurred during their radiation in the late Eocene-early Oligocene era in which body size actually decreased but brain size increased. This evolution in brain size is suggested to partly be a response to social forces, in that functioning within a larger or more complex community requires higher social effective functioning, to include communicating and collaborating with others.

MRI studies show that cetaceans have complex patterns of brain wrinkles, more so than any other mammalian group. The cetacean neocortex, closely associated with higher cortical functioning in humans, includes the limbic, paralimbic, and supra limbic regions. The neocortex shows an increased ratio of glial cells (non-neuronal helper cells) to neurons, exhibiting an increased need for synaptic efficiency in a complex brain.

Their peculiar cortical cytoarchitecture is explained to accommodate different functional strategies that other terrestrial mammals do not require, like coordinating echolocation.

Researchers often speak on the relation between cetacean and primate intelligence to suggest that although their paths were evolutionarily divergent, they have convergent development of higher intelligence.  For example, cetaceans have a high degree of regional parcellation, or designated brain areas, that are comparable to large-brained terrestrial mammals, such as carnivores or primates, like ourselves.

            Other specific features of cetacean neuroanatomy strongly suggest intelligence similar to primates. Cetaceans have expanded insular and cingulate cortices, which are both associated with higher-level cognitive functions, including attention and social awareness. Additionally, cetaceans with the largest brains retain a special layer of spindle neurons in a deep layer of their anterior insular and cingulate cortex.

These neurons are known to serve social cognition and were previously thought to be unique to humans and great apes. Researchers, however, have published that there "is no evidence that cetacean and primate prefrontal cortical analogs [are] located in the same region of the brain.”

            Overall, features of cetacean neuroanatomy support advanced cognitive capacities, and are used to prove or explain behavioral complexity (metacognition, self-awareness) and social complexity (cooperation, cultural transmission, tool use). These qualities are primarily observed in dolphins, which are well studied in a laboratory environment.

           Researchers recently showed that dolphins have mirror self-recognition or MSR, to support cetacean self-awareness. Previously only exhibited in humans and great apes, two bottlenose dolphins were provided with mirrors to observe themselves, and then were marked. They swam to the mirrors, and twisted and turned to specifically examine the parts of their bodies that were marked.  Metacognition, or “thinking about thinking,” is a complex capability attributed to humans but is also observed in dolphins. When a captive dolphin was asked to discriminate between high and low pitch, he chose the “uncertain option” on difficult discriminations, just as a human would do. Dolphins have many practices that show higher cognitive capacities, such as understanding gestures, like the human point gesture, learning symbols for their body parts, and can maintaining working memory.

Behavioral imitation supports cetacean social awareness, which includes recognizing others’ motor behavior and then mediating the relation of body parts to reproduce an action. Difficulty increases when dolphins mimic humans, as they must make analogs, such as their tail for a leg, etc. A particular dolphin at the Marine Mammal Institute in Mississippi even shows she can make predictions. The dolphins are trained to pick up trash at the bottom of the tank in exchange for fish, but instead she hoards trash under a rock, and only brings up pieces when she sees a trainer to maximize her fish return.

Behaviors in the wild also suggest overall intelligence and social adeptness. Dolphins teach foraging strategies to their young, and distribute the knowledge of tool use. For example, using marine sponges to forage is tracked back to a single mother who taught it to her daughter, who then taught it to her daughter, transferring the knowledge through vertical social transmission.

The overall indication of these capabilities is that cetaceans maintain “flexible minds” that are able to adapt and learn – intelligent minds. While many questions of their neuroanatomy are unanswered, such as what specific areas of their brain are human analogs to enlighten their individual function, they certainly are remarkable and interesting creatures.

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