Today at Discovery News you can find out why dolphins are now believed to be the world's second most intelligent animals, with only humans displaying greater brainpower.
Intelligence itself is a very loaded issue. It's difficult to compare one individual's brilliance with that of another within the same species, much less to attempt to compare intelligence among multiple species. Intelligence is just one component of a species' survival, so one can argue that spiders have evolved to be as smart as they need to be for their species to continue, rats are as brainy as they need to be, and so on.
If human standards for intelligence are applied to non-human animals, however, dolphins come very close to our own brain aptitude levels, suggests Emory University dolphin expert Lori Marino.
She's performed MRI scans of dolphin brains. The scans prove dolphin brains are:
big, relative to body size
intricate, with a neocortex "more highly convoluted than our own"
structured to allow for self-awareness and the processing of what Marino calls "complex emotions"
All animals share the capacity for emotions, she explained, but the part of the dolphin brain associated with processing emotional information is particularly expanded.
Why then did dolphins evolve to become so brainy?
Marino and her colleagues have analyzed modern dolphins and remains of ancient marine mammals to help answer that question.
The first jump in brain size happened 39 million years ago, when odontocetes (members of an order that includes dolphins, toothed whales, sperm whales, beaked whales and porpoises) diverged from their ancestral Archaeoceti group. When this split occurred, body sizes for some decreased and brain sizes increased, especially in the ancestors of modern dolphins. This coincided with the emergence of echolocation, so improved communication skills likely were tied to the brain size boost.
Fifteen million years ago yet another brain growth spurt happened. Marino and her colleagues speculate that changes in social ecology—essentially the dolphin's social lifestyle—probably contributed to the process. For example, the more a dolphin needed to communicate, benefiting its survival, the more its brain evolved to permit that interaction.
Moving to the present, dolphins have brains that are about "five times larger for their body size when compared to another animal of similar size," Marino said. "In humans, the measure is seven times larger—not a huge difference."
She concluded, "Essentially, the brains of primates and cetaceans arrived at the same cognitive space while evolving along quite different paths."
As a footnote to the above, it's important to remember that killer whales, also known as orcas, are actually the largest members of the dolphin family. Since this piece first ran, killer whales have been scrutinized due to a killer whale attack at SeaWorld. Trainer Dawn Brancheau died in the incident, which is still under investigation.
Lori Marino recently commented on the death, telling the Los Angeles Times: "I'm not trying to second-guess what was in this particular whale's mind. But, certainly, if we are talking about whether killer whales have the wherewithal and the cognitive capacity to intentionally strike out at someone, or to be angry, or to really know what they are doing, I would have to say the answer is yes."