What's a fast way to clue the audience into a character's super-intelligence, either inborn or suddenly-gained? Why, give them a swollen (and often hairless) cranium, apparently housing a grossly enlarged brain. Variants include the head being fissured like a human brain, or the enlarged brain being exposed. The head may or may not pulsate, and the rest of the body be comparatively weak and underdeveloped. Often related to Evolutionary Levels or dubious experiments done For Science!. May involve the development of Psychic Powers if it's big enough.
This is also sometimes used as a generic "alien trait" and not a specific indicator of intelligence. The Greys are a prominent example.
While this may seem like Truth in Television, since animals with larger brains do tend to have a higher intellect than those with smaller cerebra, it turns out that intelligence is much more complicated than that (otherwise blue whales, with brains the size of fully-grown adult humans, would be the most intelligent species on the planet). Turns out that intelligence is a function not so much of how large an organism's brain is, but how densely interconnected it is. The denser the brain tissue and the more neural pathways within an organism's brain, the higher its intellect. Obviously, however, a larger brain does have more room for such connections, but it's not as straightforward as this trope would have you believe.
See Also Forehead of Doom, which may be used to show this in a more realistic light.
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Anime and Manga
Void, the leader of the God Hand from Berserk is a particularly nightmarish example.
Exedore/Exsedol's retconned form from the Macross universe (left out of the Robotech continuity).
Evil telepath and Fearsome Five member Psimon has his exposed brain covered by a clear shell. In Salvation RunThe Joker can't help but smash it.
Green Lantern villain Hector Hammond's brain is huge — to the point that his neck can't support it. As such, he's confined to a special chair. Over the last few years, he's gone from "unusually large, ovoid head" to "big square head twice the size of the rest of his body."
The Leader, one of the Incredible Hulk's main villains, whose Ultimate Marvel version combines this with a totally useless body. He even needs a metal frame to keep his head from snapping his neck. While other gamma radiation mutated characters had their physical strength enhanced, the Leader instead was given Super Intelligence.
Brainchild, the ringleader of the Savage Land Mutates. He's also short, skinny, and physically feeble.
Uatu the Watcher. In his first appearance, his head was only slightly out of proportion with the rest of his body, but his design evolved until he was a tall skinny man whose head made up half his body mass.
The Futurist and Alpha the Ultimate Mutant were both hyper-evolved into bighead superintelligence. This is lampshaded when they are both prisoners on an alien planet and become friends.
Yuri's son Kondrati, who inherited his father's deformity (and capacity for Evil Genius), chose to blame the Hulk for his father's death, and became the villainous Gremlin. As the second Titanium Man, he died during Iron Man's Armor Wars rampage.
Reed Richards did this to himself once in Fantastic Four: 1234 by Grant Morrison. In order to defeat Doctor Doom in a 4-dimensional chess game that was threatening to destroy the Fantastic Four, Reed used his stretching powers to literally grow new structures in his brain in order to out-think Doom.
The Mekon of Mekonta, arch-villain of the British Dan Dare comics (once the page image), specially bred to be his civilization's Supreme Scientist and ruler, exemplifies this trope with his huge head and withered body.
An early storyline in Bongo's The Simpsons comics had most of the cast becoming superheroes; Maggie became "Brainbaby"
DN Agents villains Ape-X and Doctor Vlasov both had huge craniums; Vlasov's was under a huge glass bubble helmet for full Squicky visibility.
E-Man 's first foe, The Brain From Sirius, was nothing but a gigantic Brain in a Jar the size of a house!
Appropriately, this is the appearance of Veidt's fake alien in Watchmen
One of Charon's "ligis-bearers" in Negation has a big brain. By an amazing coincidence, he's also the team's telepath.
The cover story in issue 93 of Tales of the Unexpected involved this guy who invented an "evolution-devolution" ray then accidentally got caught in both beams at once, resulting in his head "evolving" into larger and more grotesque versions while his body was "devolving" into that of a prehistoric man/ape/etc. Eventually, his brain became so super-advanced that he was able to repair the broken device telepathically.
In All Fall Down, IQ and IQ Squared had extra-large heads while they were super-geniuses. Their craniums were reduced to normal in The Fall.
Played straight in Invincible with Angstrom Levy, after an accident left him with brains bulging out of his skull (and two more on his shoulders, though he had those removed with surgery).
In Big Bang Comics, the Pantheon of Heroes mirrors the Legion of Super Heroes; their equivalent of Brainiac 5 is Brain Boy, whose bald head holds a huge brain. Thinking hard enough makes it get even bigger.
The iconic Metalunan Mutants from This Island Earth; their humanoid masters might also qualify as a more subdued example of the "super-smart" type.
Possibly an inversion, as the Mutant didn't seem to be very smart.
Explicitly invoked in Mars Attacks!! - though possibly a subversion as when the scientists later actually study a Martian corpse they find the head seems to be full of green slime.
Brains typically are near-liquid, anyway.
In Sky High Dr. Medulla, who teaches Mad Science, has a huge head.
The Coneheads are extremely intelligent and have huge heads shaped like cones.
In the 1969 movie Le Cerveau, David Niven plays the role of the master-criminal known as The Brain. While his head isn't any larger than normal, his brain is apparently so heavy that when he is stressed out, his head falls to one side.
Megamind. One of the taglines was "It's big for a reason."
Starship Troopers 3: Marauder. The huge brain bug that takes up an entire planet, "Brain of Brains," also known as "Behemecoatyl".
"The bug is big."
In Edmond Hamilton's The Man Who Evolved, a scientist has accelerated his own evolution. Five examples are shown; first a giant human, then two cases of the trope, then a naked brain.
Taken to its logical conclusion in Last and First Men where the Fourth human species were basically giant, immobile brains. They were created as the equivalent of computers, and naturally rebelled against their creators. But in an interesting subversion, having wiped out the Third species they realized that their intellectual powers were crippled by the lack of bodies and created a Fifth species that was closer to natural humanity.
Earlier in the novel, we meet the Second human species early in their evolution, when they had evolved larger brains than the First Men (that would be us) but unfortunately hadn't yet evolved larger skulls. It basically drove their entire species insane and almost wiped them out, leaving behind only a very twisted literary corpus for future generations.
Chessmen of Mars, one of the John Carter of Mars books, gave us the Kaldanes, who look like oversized heads with crab legs and tend to travel around on rykors, creatures that look like idealized human bodies without heads. The result appears as this trope.
In "The Giant of Mars", the novella forming the first half of the final book in the series, this trope is inverted with Pew Mogel, an Evil GeniusArtificial Human, who keeps his brain elsewhere and thus has a ridiculously tiny head.
Used horrifically in C.S. Lewis' That Hideous Strength, where the evil scientists have taken the head of an executed criminal and are keeping it alive(-ish) it to channel demonic forces; they've removed the top of the head and its "augmented" brains are bulging out over the top, pulsating under membrane.AAARGH.
It's a plot point in Evolution's End, a 1941 short story by (IIRC) Robert Arthur. In a far future, humans have evolved into huge-headed, hyperintelligent and emotionally devoid beings. One of them invents a machine that accelerates evolution, tries it on some volunteers and is horrified to discover that in 100,000 years human brains will grow big enough to collapse under their weight. Also a textbook example of Evolutionary Levels.
December 1953 edition of Mechanix Ilustrated magazine. In the article "How Nuclear Radiation Can Change Our Race", Otto Binder speculated that the radiation from a nuclear war might cause mutations that could lead to the creation of a new species, Homo Superior. Among other differences, they would have brains (and heads) 50% larger than a normal human's. See the original article here: page 1◊, page 2◊, page 3◊ and page 4◊.
Jeeves's head bulges out slightly at the back, and Bertie believes that this is a sign of his intelligence. He also attributes the size of Sir Roderick Glossop's head, which resembles "the dome of St. Paul's", to his vast intellect: "I suppose he must have taken about a nine or something in hats. Shows what a rotten thing it is to let your brain develop too much.”
Similarly, in 'The Adventure of the Blue Carbuncle', Sherlock Holmes deduces that the owner of a certain hat must be an intellectual because his head is bigger than Holmes's. "It is a question of cubic capacity. A man with so large a brain must have something in it."
Happens temporarily to Xander as the result of a "spell of intelligence" in Power Rangers Mystic Force. It was depicted with a fishlens effect distorting part of the actor's head instead of prosthetics.
Calvin and Hobbes. In one arc this is an "unanticipated physiological consequence" of the thinking cap Calvin uses to give himself an intelligence boost. Strangely, this doesn't seem to alarm his parents. Then again, they never notice anything, anyway.
One comic had the cops rushing into the villain's headquarters, which had your typical My Brain Is Big guy as well as some huge-bodied, tiny-headed mooks and shouting, "Who's the brains of this operation?" And here it is◊.
In another strip, Larson inverted it, by having a student with a head half the size of everyone else asking to be excused from class because his "brain was full".
And in another inversion, a stegosaurus lectures other dinosaurs:
"The picture's pretty bleak, gentlemen. ... the world's climates are changing, the mammals are taking over, and we all have a brain about the size of a walnut."
Mortasheen subverts this with the Abcoulix, which has a giant brain not for purposes of intelligence, but rather for the purpose of generating electricity, as the Abcoulix was designed as an organic battery. This is played straight, however, for Krankenhyde.
Warhammer 40,000 has Tyranid Zoanthropes which have stunted bodies with tiny vestigial limbs and a xenomorph like head with extra brain sticking out the back. It uses its psychic powers to float around and act as psionic artillery.
Double Subverted with Orkses. Their brains are bigger but are less intelligent than humans. However, the larger ones are more intelligent than the smaller ones.
Champions adventure V.O.I.C.E.. The villain Le Maistre has a bulging head, is highly intelligent and has psychic powers to boot.
In GURPS, using Brain Tissue Grafts (from the Bio-Tech sourcebook) to increase your intelligence has the side effect of giving you a bulgy forehead. For a more cinematic option, there's the Genius Machine in Warehouse 23; the higher setting replaces the user's cranium with a big transparent dome, giving others a good view of his pulsating rebuilt brain.
Ghostbusters adventure Hot Rods of the Gods. If a Ghostbusters fires his proton pack at Meera at the same time as Meera shoots at him with the red devolvo ray, it will reverse the polarity,causing the Ghostbuster to evolve into a superior being with increased intelligence and a large head.
Averted in the Resident Evil series. Lickers have a large, exposed brain but while they're more intelligent than the zombies they were made from (to the point where they can follow orders), this isn't saying much.
The Spider Mastermind and the Arachnotrons from Doom and Doom II
Also, the Terachnoids from Ratchet & Clank Future: A Crack In Time ... Who actually have multiple brains. They've been voted smartest race in the universe for 3,000 years, and weakest race for 4,000 years.
The Nihilanth from Half-Life. There are also similar enemies called Alien Controllers.
Immediately subverted though: whatever that organ is, it's probably not where they keep their brains, given what they proceed to do with their heads.
Heimerdinger in Leagueof Legends has this in quite ridiculous proportion since he is a very small humanoid with a very large brain.
In Pajama Sam: No Need to Hide When It's Dark Outside, the titular Sam can mix up some chemicals to create a potion that increases his intelligence - and his brain size, to the point that it weighs too much for him to lift his head from the table.
Dr. Neo Cortex and Dr. Nitrus Brio of the Crash Bandicoot series fit this trope.
The aptly named "Cranium Rats" from Planescape: Torment have large brains partly sticking out of their skulls. They also form psychic networks when near each other. One of the sort-of Big Bads of the game is a colony of THOUSANDS of these rats, aptly named "Many as One".
Not to mention Master Billy Quizboy, Boy Genius. Really a middle-aged little person with hydrocephaly, but in all fairness he's a competent surgeon and good with mechanical prosthetics.
A few episodes of Big Guy and Rusty the Boy Robot had a giant scientist that got in the way of a particle beam and a spider (or something) that could suck out people's brains. With each brain that he absorbed, his head got bigger. Also, the company's CEO's nephew (a teenage Expy of the CEO) also got in the way of the particle beam, and received the same power.
The super-intelligent Omnitrix aliens in Ben 10 and Ben 10: Alien Force, Grey Matter and Brainstorm respectively, have proportionally larger heads than Ben's other forms. Brainstorm can actually open the top of his head to shoot lightning from his brain as his main mode of attack, and its brain makes up something like 90% of its body.
Fridge Logic actually makes Grey Matter more of an inversion: his eyeballs are so huge in comparison to the rest of his face that there can't be that much room for a brain left over.
In The Penguins of Madagascar, Kowalski invents a device to make himself smarter, and it gives him an inflated cranium. Unfortunately, not only is the effect temporary, it actually deflates his head entirely, leaving him a dimwitted pinhead.
Happens to Skeeter during an Imagine Spot in "Doug's Brainy Buddy" because Doug didn't understand any of his attempt to explain Kant's A Critique of Pure Reason, and also it never occured to him (or anyone else) that Skeeter was that smart.
Cybron from Skysurfer Strike Force complete with glass dome head. Only the brain is cybernetic and stolen from his old job, an A.I. lab.
The Leader◊ from The Avengers: Earth's Mightiest Heroes, much like his comic book version. Notably, in his first appearance he's exposed to gamma radiation at the moment of his defeat, enlarging his brain further to the point he can't stand up.
This has been the cause of much dispute among the scientific community about whether or not size really does matter. On one hand humans have a larger brain than most of the world's creatures, then again, so do sperm whales and elephants note although humans have most vertebrates beat in brain-to-body mass ratios.
Women on average have smaller brains than men, but they make up for it with denser neuron distribution. Proportionate to body mass, there's little difference between men's and women's brain mass. Especially when you exclude fatty tissue (which women have more of due to breasts being almost entirely fat, and which don't contribute much in the way of sensory input for the brain to process) from the body mass.
Subverted by Neanderthals: While they had a brain size comparable and even slightly larger that those of modern humans, the shape of the skull was quite lower that ours, and the visual effect was the opposite of this trope.
An old theory credits this trope with why the Industrial Revolution occurred in Europe. Since Europeans are outsized by the Xhosa, Buryats, Iroquois, Eskimos, and Mongols, it's obviously long since been discredited.
The Corvidae, crows and ravens have brains the size of a walnut, yet are almost as intelligent as the great apes. Which just shows that the Brain/Body ratio is a lot less reliable when applied to non-mammals. (Also, why you shouldn't say "bird brain" to mean "stupid".) Birds use different brain regions for "thinking" than other creatures, so you really can't judge them by the size of their frontal lobes.
The brain has to process the sensory input from the whole body, and elaborate an appropriate motor response. Seeing that cell size and cerebral cortex structure don't change with body size, and that larger animals have quite a bunch more of sensorial structures; the brain has to be larger and with an even more folded surface just to process the incoming information. Doesn't take away the fact that Hominids, Elephantids, Delphinids or Corvids have larger than expected brains and extensive processing areas.
This is often a consequence of hydrocephalus, which is caused by cerebrospinal fluid being prevented from draining out of the brain. This enlarges the ventricles that normally hold the fluid and pushes the rest of the brain outwards. If it occurs during development, the skull enlarges to accommodate the larger brain. However, the buildup of pressure actually compresses the brain tissue and in severe cases can cause mental retardation.
Conan who self deprecatingly refers to his "big fat Irish head" studied history at Harvard and wrote a thesis on the use of children as symbols in the works Of William Faulkner and Flannery O'Connor.
In his book The Dragons Of Eden, Carl Sagan notes that the species with large brain-mass to body-mass ratios tend to be those that most biologists think of as the most intelligent. Then again, this is based on subjective perception (scientists still disagree about how to measure animal intelligence), so another possible interpretation is that humans are subconsciously Wrong Genre Savvy.
Research has shown that people with autism can have as many as 60% more neurons in their brains than most people. A major theory is that the "pruning" of excess neurons that normally occurs in development goes awry, leading to an overburdened and disorganized system.
To an extent, a big brain helps a species of smaller mammals (below 10 kg or so) avoid extinction when the environment changes, according to a study reported in an article in Nature.