Excerpted from David Kaiser
The largest brain ever to appear on the planet belongs to the sperm whale (Physeter catodon), a member of the Cetacean Order, whose brain can weigh up to 9200 g, with an average of 7818 grams. One scientist has suggested, solely on brain weight, that the sperm whale possesses a higher development of conscious-ness than humans, despite a relatively low brain-to-body weight ratio: 37,093.0 kg to 7.8 kg, (Lilly, 1967). Opinions vary as to how indicative brain size and other neuroanatomical correlates are of brain function and overall intelligence. How to measure a creature's intelligence, or level of consciousness or sapience, is problematic (as noted by cf. Jerison, 1986); the relationship between the brain and the mind is not an obvious one. Ignoring dualist arguments, consciousness is a brain function, a product of a specific organization of neural groups, but its anatomy and phylogeny are unclear. Consciousness in its present form in Western cultures may have emerged recently, during historic times but features of consciousness may be prevalent to different degrees in other mammals, specifically in larger-brained species such as apes and higher primates, carnivores, elephants, and whales.
Dolphins demonstrate many behaviors that show signs of conscious awareness. For instance, behaviors which are illicit and punishable are often performed only when a dolphin believes no one is around (e.g., Savage-Rumbaugh and Hopkins, 1986). When a dolphin squirts water at a human (to show annoyance), he will often raise his head out of the water to curiously observe the effect his behavior had on the unsuspecting victim (personal observation). Both examples show an awareness of effects one's behavior has on others. They also have voluntary penile erections, which may suggest that they are conscious of things of which humans are not.
Whatever cases are made for or against dolphins possessing human-like sapience, it is interesting to remember that they already possessed their present mental life (presumably) 15 to 25 million years ago.
This belief that mental experiences are a unique attribute of a single species is not only unparsimonious; it is conceited. it seems more likely than not that mental experiences, like many other characters, are widespread, at least among multicellular animals, but differ greatly in nature and complexity. -- D.R. Griffin, 1981.