Dolphins’ Cognitive Abilities
Dolphin have greater cognitive abilities than great apes and at least the cognitive abilities of bottlenose dolphins rival human cognitive abilities in some aspects. They may exceed ours in some aspects but we overcome them in other aspects.
Dolphin brain have a similar size to ours in relation of their size. Their neocortex has a different structure than ours, is thinner but it has much more area and is more folded. They also have more neurons than us in their neocortex. Humans have between 12000 millions and 18000 millions neurons in neocortex. Chimpanzees have 9000 million neurons and elephants 5800 millions neurons in their neocortices regardless of their big brain.
On the other hand Pilot whales ( a dolphin species ) have 37200 millions neurons in their neocortex, bottlenose dolphins neuron numbers have not been measured yet but knowing they have 0.65 times pilot whales cortical area but double them on neuronal density we can calculate the neurons number in bottlenose neocortex in 48000 millions neurons.
Their evolutionary process favored the extreme gyrification that is observed in the cetacean brain since highly folded cortices are those that have more neurons connected through the white matter (i.e., a higher non-local connectivity), which leads to a thinner cortex because it offers less mechanical resistance to folding, but at the same time leading to the remarkable large brains that are currently observed in dolphins.
Dolphin different neocortex structure allow more interconnections between areas than human thicker 6 folded neocortex. This allow dolphins to process complex sensory stimulus and complex cognitive functions much faster than humans. But it has a cost, dolphin brain have a higher energetic cost per gram than human brain.
https://pdfs.semanticscholar.org/b479/e0afc07806486b1a11c8d37efbf2065458d.pdf
Some authors have suggested that dolphins developed their large brain because echolocation is very complex and requires great processing capacity. If this were the case, most of the cerebral cortex of the dolphin would be occupied by the auditory cortex. However, this is not the case, although the auditory nuclei of the dolphin brain stem are larger than those of any terrestrial animal, its primary auditory cortex is the same size as its visual cortex and is not larger than the auditory human cortex, while that associative areas (which are important for cognitive functions) occupy a proportion of the cerebral cortex similar to human or even greater.
Quantitative relationships in delphinid neocortex.
Cetaceans Have Complex Brains for Complex Cognition
Dolphins evolved big brains to develop higher cognitive abilities that they need to manage their complex social life and their complex language.
Dolphin brain cortex is organized functionally very differently than human cortex. For more detail read my answer to Neuroscience: How is the dolphin occipital lobes different from that of humans?
Dolphin cognitive abilities could be subestimated because they don´t have a precision manipulation organ like our hands or fine motor abilities, so they are very limited for tool use
But there is evidence that they can understand concepts that even chimpanzees cannot.
A dolphin can understand complex sentences. For example they can understand the difference between the order “put the right ball in the left basket” and “put the left ball in the right basket. They can understand spatial concepts like on, under, behind, inside outside etc. They can even understand the concepts of time organised future or past in the form of yesterday and tomorrow.
Chimpanzees can learn at least 2000 words or more but they cannot understand novel sentences neither can understand the concept of right and left.
Both dolphins and chimpanzees can recognize themselves in the mirror but only 50% adult chips can manages to do it after more than 100 trials.
Dolphins recognize themselves in the mirror from their first trial and 100% manage to do it. And they also recognize themselves since they are 6 month old even at younger ages than humans.We start recognizing ourselves at the mirror at 18 month.
http://journals.plos.org/plosone...
Dolphins also have a very complex language. They use signature whistles in a way similar to our names to identify individual dolphins or groups of dolphins.
Male bottlenose dolphins use own ‘names,’ study finds | DW | 08.06.2018
Their language is also like ours, hierarchically organised and open.
That means they can combine elements in different orders to produce different meanings, they combine elements in blocks of at least 7 orders of hierarchical organization. We combine phonemes to produce words, words to produce phrases, phrases in to sentences, sentences in to paragraph, etc. that´s the hierarchical organization. Dolphins produce simple elements that are individual whistles or pulsed sounds and they combine them to form blocks of first order. They combine 1st order blocks to form 2nd order blocks, etc. Stable blocks of up to 7th order of complexity have been evidenced.
They can combine blocks of different order of complexity to produce an almost unlimited number of signals. Most of their signals are composed of 5 to 7 blocks independently of their complexity but they produce signals with 2 to 24 blocks.
They can also produce up to 4 different sound simultaneously so they can combine blocks not only by linearly ordering them like our speech but also superimposing them. Most blocks has 1 or 2 superimposed simpler blocks but they can form blocks with up to 4 simultaneously superimposed blocks. Dolphins never start 2 superimposed blocks simultaneously, The block winch start first is called the base and usually is stable, the block that superimpose to it is called the superstructure and is highly variable. The base can end before the superstructure and the superstructure can become the base for a new superstructure, this is called inversion. This increase considerably the complexity of dolphin language to a grade that even our speech don´t reach.
We only have deciphered the meaning of signature whistles but those are only the simpler signals dolphins produce, signature whistles don’t reach the complexity of 1st order blocks they are basic elements. Dolphin signals have the capacity to encode at least 6 times more information than human language. Some authors suggest that dolphin language encodes up to 100 times more information in the same time.
https://cocosci.berkeley.edu/jos...
https://ac.els-cdn.com/S24057223...
https://pdfs.semanticscholar.org...
Dolphin language also has a complex grammatical and complies with zip´s law.
Other cognitive ability is metacognition. Metacognition is the ability to realize others have a mind and can have belief. There are different levels of metacognition, the higher level is what is called the false belief test which test the abilitie of recognize that other can have a false belief about something also called the Sally-Anne test. Humans start passing the false belief test at 5 years old in 90% cases and 4 years old 10%. Great apes, autistic and schizophrenic patients don´t pass it.
In 2006 a research group have done a metacognition test similar to Sally–Anne test of 6 dolphins in a south African dolphinarium. All passed the test in the first trial but the paper wasn’t accepted because the peer reviewers weren’t sure if the dolphins could have cheated in any way so the researchers try a different version of the test but dolphins refuse to perform again. That work was published as a master thesis but not as a peer reviewed paper. Nevertheless Great apes, lower than 4 year child, autistic and schizophrenic patients did´t past the same version of the test.
Dolphins also use sounds to produce images of their underwater environment. That´s called echolocation.
Dolphins can identify objects using echolocation. They can produced high directional click sounds that give them the ability to detect prey. A bottlenose dolphin can differentiate:
- 2 metal bars with a difference of only 0.2 millimeters in front of them,
- two 1 cm objects (a B-B pellet and a kernel of corn) at 15 meters from them
- detect a 5 cm ball 60 meters in front of them
- a cod at 135 meters far away
- a human diver 600 meters far away.
Bottlenose dolphins can distinguish between materials with different density and hardness. But dolphins echolocation only work underwater, so they usually cannot echo-locate over the sea surface. objects must be underwater to be echo-located. But some dolphins have solved that by swimming at a certain speed in calm water they can create a wave over their melon which can focus the sound beam in the air to echo-locate objects over the waterline.
This photo shows a bottlenose dolphin using such strategy to eco-locate over the water, and since the echo-locating beam is deviated 10 degrees to the left in bottlenose dolphins this one is eco-locating the photographer.
I like a lot this photograph because in one side there is a professional photographer using a high tech camera to see a dolphin who is using a high developed echolocation tactic to observe the human. Each one is using their most advanced skills to observe the other.
Dolphins have very complex social structure that varies from one population to other with cultural differences even between simpatric populations of the same species. Chimps form groups with a complex structure that vary from chimpanzees to bonobos but they are different species separated by 1 million years of evolution. But all chimp population have the same social structure and all the bonobos too. They have some variation in the tool use that is transmitted culturally but is limited. Dolphins have a huge variability in lot of behaviors and social structure between and within groups that also are transmitted culturally. Here are some examples:
https://aquaticmammalsjournal.or...
All Mothers are Not the Same: Maternal Styles in Bottlenose Dolphins (Tursiops truncatus)
Preparing the Perfect Cuttlefish Meal: Complex Prey Handling by Dolphins
Dolphins also recognize themselves by name something that chimps don´t do and form multilevel social alliances something that´s only humans and dolphins do and not chimps.
Bottlenose Dolphins Retain Individual Vocal Labels in Multi-level Alliances.
So dolphins have greater cognitive abilities than great apes and at least the cognitive abilities of bottlenose dolphins rivals humans cognitive abilities in some aspects. They may exceeds ours in some aspects but we overcome them in other aspects.
We still know very little about dolphin cognitive abilities and unlike the great apes their limits haven`t been found yet. Each new study show they have greater cognitive abilities than they were suppose to.
