New research into the mental capacity of dolphins has suggested that it is dolphins rather than chimpanzees that are the animal closest in intelligence to humans.

A leading US researcher in this field, Lori Marino of Emory University, Altanta, Georgia has used magnetic resonance imagery to scan dolphin brains and concluded that their brain neuroanatomy suggests “psychological continuity between humans and dolphins that has profound implications for the ethics of human-dolphin interactions.”

When it comes to correlation with intelligence, brain size relative to body size is more significant than absolute brain size. Marino and colleagues found the brain cortex of bottlenose dolphins so large that “the anatomical ratios that assess cognitive capacity place it second only to the human brain.”

Behaviour studies of dolphins also suggest that they have a significant degree of intelligence. For example, bottle-nosed dolphins recognise themselves in a mirror and can use the mirror to look at various parts of their bodies. Dolphins are able to learn simple symbol-based language. Wild dolphins live in groups that have complex social structures and emotional sophistication and when hunting, dolphins co-operate with great precision to herd shoals of fish.

A recent study followed how an injured wild dolphin that was placed in a dolphinarium to recuperate, where it was taught the trick of tail-walking. When it was released to the wild again, scientists continued to observe the group it joined, and watched with amazement as the trick of tail-walking spread through to the other dolphins.

Some scientists are so impressed by the mental capacity of the dolphin that they believe dolphins should be recategorised and treated as “non-human persons.”

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