Technically, humans are the smartest animals.
Monkeys are usually considered the most intelligent aside from people. Which makes sense considering they share something like 98% DNA with us.
Copied from Yahoo answers
dolphins have a number of advantages over other animals. they are self-aware, which means they know when they look in the mirror they are seeing themselves instead of another dolphin, which is rare in the animal kingdom. they learn by observation - if you teach one dolphin a trick, the dolphin in the next pen often is able to perform it also, without any direct instruction. they understand that when humans point, they want you to look at what they're pointing to, not their hand (no other animal gets this one) and in fact, they point things out to each other with their echolocation beams in the wild. when they are shown a tv screen, they understand the images as a representation of reality and not just a pretty light show. they can mimick humans, and know that their fluke is the equivalent to our legs. most importantly, they have language, in my opinion.
they have names, which are used to call them and which they use to introduce themselves. they understand the significance of word order, and other basic grammar. they understand such abstract and relative concepts such as left, right, other, same. if this doesn't sound hard to you, remember they have to learn it through signals and try to imagine you're playing pictionary and you have to signal "other" or "left". how hard would it be for you to sign "left" and how hard would it be for the other person to figure out what you're signing? now think that your partner is a foreign exchange student who doesn't speak one word of english and you can't use word associations. sound like a challenge yet? dolphins somehow managed to figure out those signs from their trainers, and put them together in a concept such as left, which is not only abstract (left is not something with physical existence, it's a concept we made up), but relative (your left and my left are different).
so in my book, either they already knew this relative concept and used it (and so learning the signal for it is like your foreign exchange student figuring out what your signals mean) or they had to figure out a concept they knew nothing about from signals (which would be something like your foreign exchange student's 3 year old child, who still hasn't learned left from right, figuring it out). either way, it shows that they are capable of abstract thought, and that they have some awreness of relativity.
Speaking of Humans
Good support for the theory:
Humans are the only land animals with a dive reflex.
Most land mammals have no conscious control over their breathing. The voluntary control humans have over their respiratory system can be compared to that of (semi)aquatic mammals which inhale as much air as they need for a dive, then return to the surface for air. Morgan argued that this voluntary breathing capacity was one of the preadaptations to human voluntary speech.
Human facial structure is quite different from other apes, with thick eyebrow hair and downturned nostrils. The shape of the human nose, with nostrils running perpendicular to the rest of the face, prevents water from entering the nose while upright. Thick eyebrows allow water to flow from the top of the head away from the eyes upon surfacing, allowing for faster adjustment to vision through air. Human facial hair forces water to flow away from and around the nose and mouth to enable faster inhalation upon surfacing.
Dramatic increase in skull size is a prominent theme in human evolution, making childbirth difficult and dangerous. Water birthing is believed to facilitate childbirth and to reduce risks to mother and infant.[attribution needed]
Human infants are born covered in vernix caseosa, a waterproof coating not found in any other land mammal. A radio programme on the AAH (Scars of Evolution, Episode 2) aired on 2005 postulated that if vernix is due to Human's aquatic origins then other aquatic species may also show this phenomenon. The programme searched for this evidence and found a report of common seal also being born with a layer of vernix.
Humans are the only mammal with perpetually swollen mammary glands. Human females have large fatty breasts that float on the surface of water. This would have allowed a mother to feed an infant at varying depth while the baby was kept out of the water and thus allowed to breathe normally.
Human brain tissue requires comparatively large amounts of omega-3 fatty acids, which are uncommon in the land food chain but prevalent in the marine food chain. Most animals which move to plains life tend to develop smaller brains, while aquatic animals tend to evolve larger ones, quite possibly because of access to omega-3. Omega-3 fatty acids also promote HDL cholesterol and cardiovascular health in humans, while the saturated fats in pork, beef and other land-based meats do the opposite. Yet for land-based carnivores the opposite is true and they have special digestive enzymes to neutralize the harmful effects of dietary cholesterol. It is noteworthy that many nutritionists[attribution needed] find seafood to be the healthiest protein source for humans, whereas the meat of land-based mammals such as from beef or pork are the most harmful.
Sweating and tears are prevalent in humans but not in other primates. They are considered further evidence to support the hypothesis, insofar as they are vectors for the removal of excess water and salts from the body as might result from the ingestion of saltwater (as in eating food from a salt marsh). Other alleged former marine animals, such as the elephant, cry saline tears, and the mechanism by which humans produce sweat from eccrine glands could have developed as a means of shedding extra salt.
The most common human mating practice, ventro-ventral ("missionary position" or "dolphin-style"), is essentially front-to-front, exactly how aquatic mammals must mate. Few other land animals (bonobo, orangutan, potto, sloths, all arboreal) use such a position more or less frequently; instead, mating coitus more ferarum is the norm, as with, for example, dogs. Marine animals, even non-mammals, also tend to develop a less accessible vagina to keep out water, necessitating a longer penis (possibly explaining why the human penis is much longer in relation to body size than any other primate penis), a trait long noted as specific to humans and bonobos (who live partially in flooded forest) among primates.
Swimming among humans and apes is not innate, and must be learned. Infants are capable of the equivalent of underwater paddling and breath hold. Humans have slight webbing between the fingers.
Also, as exercise physiologists may note, of all exercise types, swimming far and away puts the least strain on human bones and joints. Whereas running, jumping, climbing and virtually all other forms of land-based physical activity put undue and often injurious strain on human joints, swimming is rarely, if ever, deleterious to the human skeleton.
Swimming among humans and apes is not innate, and must be learned. Infants are capable of the equivalent of underwater paddling and breath hold. Humans have slight webbing between the fingers.
Humans parallel marine mammals in having multiple medullary pyramids in their kidneys. To avoid the deleterious effects of saline water dehydration, marine mammals have adaptively thickened the medullas of their kidneys – which enhances their ability to concentrate excretory salts in the urine. However, the lobulation of the kidney’s medullary region in marine mammals appears to be an adaptation to expand the surface area between the medulla and the enveloping outer cortex in order to increase the volume of marine dietary induced hypertonic plasma that can be immediately processed for the excretion of excess salts and nitrogenous waste.
A phylogenetic review of freshwater aquatic mammals suggests that most, if not all, nonmarine aquatic mammals inherited the medullary pyramids of their kidneys from ancestors who originally inhabited, or frequented, marine environments. So this suggests that most, if not all, aquatic mammals exhibiting kidneys with lobulated medullas are either marine adapted – or are descended from marine antecedents. Additionally, a phylogenetic review of nonhuman terrestrial mammals possessing kidneys with multipyramidal medullas suggests that bears, elephants and possibly rhinoceroses, also, inherited their lobulated medullas from semiaquatic marine ancestors.
Multipyramidal medullas are rare in the kidneys of terrestrial mammals and are-- non existent-- in catarrhine primates-- except for humans. And those terrestrial mammals that do have them either have coastal marine ancestors (bears, elephants, rhinos) or are capable of drinking salt water (bovines).
Most marine mammals avoid drinking sea water. And experiments have shown that when sea water is inserted into the stomachs of pinnipeds, they usually regurgitate. Most of the intake of hypersaline fluids in marine mammals is from the ingestion of marine invertebrates whose bodies are usually isotonic with their marine environments. The human kidney, however, is fully capable of excreting water with a salinity up to 3.6% salt which is higher than most marine environments. However, since the body also produces hypotonic metabolic water, any hypertonic fluids ingested would be partially diluted by the hypotonic water produced from the oxidation of ingested proteins, fats, and carbohydrates.
The human spleen, an organ that stores oxygen-rich blood, is relatively large in humans, serving as a kind of biological "scuba tank". This is suggested after studying physiological changes in freedivers; The contracted and compressed spleen adds extra oxygenated blood to the circulation.[18] The German physiologist Max Westenhöfer already noticed the resemblance of the human spleen with aquatic mammals
And heres an interesting fact. Moken can see underwater better than any other breed of Human.
And some African people have the Epicanthal eyefold. Weird.