Recent research has revealed that dolphins might be the second-smartest animals after humans. The reason cited is that MRI scans show their brains being four to five times larger for their body size when compared to another animal of similar size.
"If we use relative brain size as a metric of 'intelligence', then one would have to conclude that dolphins are second in intelligence to modern humans," Lori Marino, a senior lecturer in neuroscience and behavioral biology at Emory University, told Discovery News.
Marino, who has performed several MRI scans on dolphin brains, said that at least two other lines of evidence support her claims about dolphin intelligence.
First, various features of the dolphin neocortex - the part of the brain involved in higher-order thinking and processing of emotional information - are "particularly expanded" in dolphins.
Second, behavioral studies conducted by Marino and other experts demonstrate that dolphins exhibit human-like skills.
These include mirror self-recognition, cultural learning, comprehension of symbol-based communication systems, and an understanding of abstract concepts.
According to Marino, these findings suggest that marine park shows, "dolphin-assisted therapy" facilities and other forms of captivity "are potentially psychologically harmful to dolphins and present a misinformed picture of their natural intellectual capacities."
"This point is based on the simple proposition that the more aware an individual is of one's present and future circumstances, the more intensely one may feel the difference between a pleasant and unpleasant situation, or the more one can think about, and thus experience, negative feelings and ruminate about the negative consequences of one's circumstances," she said.
"If this proposition is not true, then there is no basis for assuming humans suffer more than any other given animal," she added.
She pointed out that during dolphin drives, when the animals are herded together by boats, some dolphins become so panicked that they die of heart attacks.
Others die from exhaustion attempting to flee, while still others become entangled in nets and are killed or injured.
The dolphins that do survive are hoisted from the water, often by their tail flukes, and transported to the human-run parks and other facilities.
"The scientific evidence on dolphin sensitivities reveals that they are vulnerable to trauma and suffering when forced to live in the confined context of marine parks," Marino said.