by Maddalena Bearzi and Craig B. Stanford
...A gorilla and a bottlenose dolphin are about as closely related as a mouse and an elephant.
In spite of these differences, dolphins and apes--and by extension ourselves--share some strikingly similar and profoundly important traits. All three groups--the various dolphin species, the four great apes, and we humans--possess the acme of brains on Earth today. With due respect to a few other brainy animals like elephants, the cetaceans--dolphins and whales--and higher primates are the most cerebral of the world's creatures. We are all highly intelligent relative to the millions of other co-inhabitants of Earth. We live in highly complex, often fluid societies which defy the easy categories that apply to most other animals. The two creatures have evolved in parallel, exemplifying what biologists call convergent evolution. Although a casual observer won't see these parallels, research on dolphins and apes has produced increasingly abundant evidence for the comparison.
...However you define intelligence, apes and dolphins are second only to humans in brainpower. Their brains are enormous in comparison to the size of their bodies. This brainpower has allowed dolphins and apes to possess communication skills and social interactions so complex that we are only now beginning to understand how they work. Unlike most animals, apes and dolphins tend to live in flexible, open societies, and the relationships among individual animals are based on long-term memory of who is whose friend, and who owes whom a favor.