When considering the intelligence of different species, a common question arises regarding brain size, particularly when comparing dolphins to humans. However, understanding intelligence requires looking beyond just the weight or volume of a brain, delving into its intricate structures, neural organization, and the complex behaviors it enables.
Absolute Brain Size and Structure
Dolphins possess larger absolute brain sizes than humans. An average adult human brain weighs between 1.3 to 1.4 kilograms. In contrast, the average bottlenose dolphin brain can weigh more, ranging from approximately 1.5 to 1.7 kilograms.
Beyond just weight, the structural observations of the dolphin brain present striking features. The cerebral cortex of dolphins, the outer layer involved in higher-level thinking, exhibits extensive folding, known as gyri and sulci. This convoluted surface creates a large cortical area, with dolphin brains having about 40% more cerebral cortex than human brains. While this increased surface area might suggest greater processing capacity, the internal organization of the dolphin cortex differs, with a thinner neocortex and a five-layer structure lacking a distinct layer IV, which is present in the human brain.
Beyond Brain Size
Absolute brain size alone does not fully determine intelligence; other metrics offer a more comprehensive understanding. The encephalization quotient (EQ) is one such measure, comparing an animal’s actual brain size to the brain size expected for an animal of its body mass. Humans have the highest EQ among all animals, around 6.56 to 7.4. Dolphins, while having a high EQ compared to many other animals, fall behind humans, with their EQ ranging from 4.0 to 5.4.
Another important factor is neuronal density, which refers to how closely packed nerve cells are within the brain. The human neocortex, involved in complex thought, contains 19 to 23 billion neurons. In contrast, the bottlenose dolphin neocortex has about 5.8 billion neurons and a lower neuronal density. Furthermore, the organization of neural pathways in dolphins is functionally different from humans. Dolphins have a relatively small prefrontal cortex, which in humans is associated with higher-level thinking, memory, and goal-setting. This suggests that despite their large brains, the specific architecture and density of neurons contribute significantly to cognitive capabilities.
Dolphin Cognitive Abilities
Dolphins demonstrate a range of sophisticated cognitive abilities. They possess complex communication systems, utilizing a variety of whistles, clicks, and burst pulses. Each bottlenose dolphin develops a unique “signature whistle” that functions similarly to a name, allowing individual identification within their social groups. These vocalizations, combined with body language, facilitate intricate social interactions and cooperative behaviors.
Dolphins live in dynamic social structures called pods, which can range from a few individuals to superpods of over a thousand members. Within these groups, they engage in cooperative hunting, social learning, and exhibit empathy towards one another. Their problem-solving skills are evident in their adaptability to complex environments and their use of tools. For instance, some dolphins use marine sponges to protect their rostrums while foraging on the ocean floor, showcasing innovative tool use and potential cultural transmission of this behavior. Dolphins also exhibit self-recognition, a rare trait, as demonstrated by their ability to recognize themselves in mirrors, a capacity shared with humans, great apes, and elephants.
Distinctive Human Intelligence
Human intelligence encompasses a unique set of advanced capabilities that distinguish our cognitive profile. Abstract reasoning is a hallmark of human cognition, involving the ability to understand and reason about concepts not directly observable, discern patterns from limited data, and apply them to novel situations. This capacity allows for complex problem-solving and the generation of new ideas. Humans also possess a highly developed symbolic language, characterized by intricate grammatical structures, enabling nuanced communication and the expression of complex thoughts.
Our species demonstrates a profound capacity for cumulative culture, where knowledge and innovations are passed down and built upon across generations, leading to continuous societal and technological advancement. This includes complex tool manufacturing, moving beyond simple tool use to design and create intricate instruments for various purposes. Humans engage in extensive long-term planning, setting distant goals and devising multi-step strategies to achieve them. Humans also exhibit a sophisticated theory of mind, the ability to attribute mental states—beliefs, intentions, desires, and knowledge—to oneself and others, and to understand that others’ mental states may differ from one’s own. These cognitive facets combine to form a distinct form of intelligence, enabling unique intellectual feats and shaping human civilization.