Dolphin IQ: How Smart Are Dolphins, Really?

There is no such thing as a dolphin IQ. IQ is a score on a human test, ranked against human norms, and no dolphin has ever been given one, so any specific “dolphin IQ” number you see online has no test behind it. What exists is evidence about behaviour and brains: bottlenose dolphins have passed a mirror test, use individual signature whistles that work like names, and pass a sponge-tool habit down the female line, and some dolphin species are more encephalised than any non-human primate. Sceptics counter that the same behaviours appear across many mammals and that cetaceans do poorly on some standard tasks. This article lays out both sides and what each finding does and does not show.

• No score: dolphins have no IQ because no normed test exists for them; comparisons rest on behaviour and brain measurements.
• Best evidence: mirror self-recognition (2001, two dolphins), name-like signature whistles (2013, wild dolphins) and cultural sponge tool use (2005, Shark Bay).
• Brains: some delphinids are more encephalised than any non-human primate, and the long-finned pilot whale has about 37.2 billion neocortical neurons, almost twice the human count.
• The counter-case: a 2013 review argues the behaviours are common across vertebrates and that cetaceans do not surpass certain benchmark tasks, so “second smartest after humans” is unproven.

Is there a dolphin IQ?

An IQ is not an intrinsic property, like weight. It is a person’s standing relative to a norm group on a specific test, which is why 100 is average by construction (see the IQ bell curve and the average IQ test score). A dolphin cannot take a test written for humans, and no comparable test with a dolphin norm group exists, so a dolphin’s IQ is undefined rather than high or low. Researchers instead compare species through behaviour experiments and brain measures such as encephalisation — brain size relative to what is expected for the body size — which is a rough proxy for cognitive capacity, not a score.

Big brains: what the numbers show

In 1998 Lori Marino compared 21 toothed-whale species with 60 anthropoid primate species using two measures of encephalisation. Humans remain extraordinary, but a subset of dolphin species are significantly more encephalised than the most encephalised primates, narrowing the gap between humans and other animals. Counting cells adds a twist. Mortensen and colleagues (2014) estimated that the long-finned pilot whale — a member of the dolphin family — has about 37.2 billion neurons in its neocortex, almost twice as many as humans, plus 127 billion glial cells. Because pilot-whale neurons are less densely packed, the larger count comes from a larger brain. The authors conclude that the absolute number of neocortical neurons does not explain human cognitive superiority. A bigger tally does not mean a higher IQ, and it does not show that pilot whales out-think people. For the human side of the same question, see brain size and IQ.

The mirror test

Recognising your own reflection is rare in the animal kingdom. In 2001 Diana Reiss and Lori Marino exposed two bottlenose dolphins to reflective surfaces. Both responded in ways consistent with using the mirror to investigate marked parts of their bodies, which the authors described as a striking example of evolutionary convergence with great apes and humans. It is a very small sample, and because dolphins cannot touch a mark with a hand, the researchers had to interpret body-inspection behaviour instead. That makes the finding suggestive rather than conclusive, but it is among the studies most often cited when dolphins are placed near the top of animal-intelligence lists. Gorillas, by contrast, have usually struggled with the same test (see gorilla IQ).

Signature whistles: do dolphins have names?

Each bottlenose dolphin develops its own signature whistle, an identity signal whose shape encodes who is calling independently of the voice itself. In 2013 Stephanie King and Vincent Janik played wild dolphins copies of their own signature whistles. The animals called back when they heard a copy of their own whistle and did not respond to whistles that were not their own. The authors concluded that this learned identity signal is used as a label when addressing another dolphin, and that bottlenose dolphins appear to be unique among non-human mammals in using learned signals as individually specific labels for social companions in their own natural communication system. Labelling with learned signals is a foundation of human language, although the study does not show that dolphins have language.

Sponge tools and dolphin culture

In Shark Bay, Western Australia, some wild bottlenose dolphins tear off marine sponges and wear them over their beaks while foraging on the seabed. Michael Krützen and colleagues (2005) showed that genetic and ecological explanations for the habit were inadequate. Mitochondrial DNA showed that sponging passes almost exclusively from mothers to female offspring within a single matriline, and the adult spongers appear to descend from one recent “Sponging Eve”. Unlike in apes, tool use in this population is almost entirely limited to one family line that lives inside a large, open social network. The authors call it the first case of an existing material culture in a marine mammal, and a reminder that intelligence in the wild is often social knowledge passed on, not a trait measured in a laboratory.

The sceptic's case

Not every neuroscientist accepts that dolphins deserve a special intellectual status. In a 2013 review in Neuroscience, Paul Manger argued that the behaviours cited as evidence for high cetacean intelligence are found commonly across mammals and other vertebrates, and that cetacean brains became relatively large about 32 million years ago and have stayed stable in relative size since, which he takes to mean that sophisticated cognition played no role in their evolution. He also points to reports that cetaceans do not surpass Piaget stage 4/5 on object-permanence tests and could not solve an “if and only if, then” abstract task, and concludes that their general intelligence may be lower than that of other vertebrates. This is a contested position, and researchers who study dolphins read the same evidence differently, but it is a peer-reviewed reminder that big brains and charming behaviour are not the same as a measured intellect.

What each finding can and cannot show

The same logic applies to every animal ranking on the internet. Our write-ups on chimpanzees, crows, octopuses, dogs and gorillas each stop at the same place: behaviours and brain facts, never a valid score.

Dolphin IQ vs human IQ

People search for “dolphin IQ vs human” expecting a number. The honest comparison has three parts. Brains: humans remain the most encephalised animals measured, though some dolphin species narrow the gap. Behaviour: dolphins show self-recognition, individual vocal labels and cultural tool use, which humans do too but most animals do not. Tests: humans can be scored on a common scale (see the IQ scale by age and the IQ level chart), whereas dolphins cannot. Human IQ is a useful, standardised measure inside its own norm group; outside it, the word only creates a false sense of precision.

Quick answers

• What is the IQ of a dolphin? Undefined. No normed IQ test exists for dolphins, so any specific dolphin IQ figure lacks a test behind it.
• Are dolphins the second smartest animal? That claim is popular, not established: some dolphins are highly encephalised, but a 2013 review argues their behaviour is not special among vertebrates.
• Are dolphins smarter than chimpanzees? No study has ranked them on a common scale; the evidence for each rests on different tests.
• Do dolphins have names? They have signature whistles that other dolphins answer, which function like individual labels.
• Can dolphins recognise themselves in a mirror? Two bottlenose dolphins did in a 2001 study; the sample was tiny.

The bottom line

Dolphins are cognitively sophisticated animals with large, complex brains, but they cannot be given an IQ, and the popular idea that they rank second only to humans is a claim, not a measurement. The best evidence is specific and interesting — mirror behaviour, name-like whistles, sponge tools passed down a family line — and the best sceptical review argues that none of it sets dolphins apart from other clever vertebrates. Both readings deserve to be held at once.

Sources

• Reiss, D. and Marino, L. (2001), PNAS 98(10): 5937–5942: mirror self-recognition in the bottlenose dolphin.
• King, S.L. and Janik, V.M. (2013), PNAS 110(32): 13216–13221: bottlenose dolphins can use learned vocal labels to address each other.
• Krützen, M. et al. (2005), PNAS 102: cultural transmission of tool use in bottlenose dolphins.
• Mortensen, H.S. et al. (2014), Frontiers in Neuroanatomy 8: 132: quantitative relationships in delphinid neocortex.
• Marino, L. (1998), Brain, Behavior and Evolution: a comparison of encephalization between odontocete cetaceans and anthropoid primates.
• Manger, P.R. (2013), Neuroscience: questioning the interpretations of behavioral observations of cetaceans.