While dolphins possess brains that are larger than human brains—both in absolute weight and in their brain-to-body weight ratio—the brain of the bottlenose dolphin, for instance, is notably larger and more complex than a human brain. This has long intrigued scientists and the public alike, prompting questions about just how intelligent dolphins really are.
Dolphins, being mammals, must breathe air to survive. Yet, they spend their entire lives in the ocean. To handle this challenge, dolphins have evolved a fascinating adaptation: only half their brain sleeps at a time. This unihemispheric slow-wave sleep allows them to remain partially conscious, swimming and surfacing for air even while resting. The “asleep” side of the brain switches every 2–3 hours. It’s an elegant solution for an animal that can’t afford to go fully unconscious. With a brain that big, some might wonder why dolphins aren’t driving cars—well, no hands!
To understand the brain’s complexity, it helps to look at neurons. Human brains contain between 86 and 100 billion neurons. Dolphin brains, on the other hand, typically contain around 12 billion, possibly a bit more. This means dolphins likely have just over 13% as many neurons as humans. Still, dolphin neurons tend to be larger than ours, contributing to their hefty brain size.
This phenomenon—big brain size not necessarily equating to high intelligence—isn’t unique to dolphins. Human men generally have larger brains than women, but this difference stems from their larger body size, not superior intellect. In fact, both men and women have roughly the same brain-to-body mass ratio. Men may have slightly more neurons, but women have more synapses, and the overall result is cognitive equality. Nineteenth- and twentieth-century pseudoscientists often misunderstood this, wrongly associating brain size with intelligence.
So, when you’re evaluating how smart an animal might be, don’t just look at how big its brain is. Instead, consider two key metrics: total neuron count—especially cortical neurons—and the brain-to-body mass ratio. These give a much clearer picture of cognitive potential. A bigger brain doesn’t always mean a smarter animal.
Interestingly, some studies suggest dolphins may have a similar or even greater number of cortical neurons compared to humans. If dolphin neuron counts exceed 12 billion, the difference between human and dolphin neurons might be narrower than the often-cited 13%. Nevertheless, dolphins still have a significantly lower brain-to-body mass ratio compared to humans. This remains one of the key reasons why scientists still believe dolphins are less intelligent overall, despite their impressive neurological hardware.
To sum up, neurons are a useful heuristic when evaluating intelligence—but they’re just one piece of a much more complex puzzle. When it comes to dolphins, their brains are indeed big and sophisticated, but there’s more to intelligence than sheer volume.
Leave a Reply