Intelligence on Earth

Also see: Intelligence, Development of intelligence

The hypothetical rise of intelligence is of great interest in speculative biology projects, not only among alien beings, but also here on Earth, where there already are a number of species that could, one day, develop greater and greater cognitive capabilities.

As established here, evolution of intelligence has five main requisites: See here a related discussion on the forum.
 * a complex nervous system (possibly not necessary for genetic sentience);
 * an energy-rich metabolism that supports said nervous system (best with high-energy food);
 * manipulator organs to hold and use tools;
 * a social organization with extensive brood care (necessary for culture, non intelligence per se);
 * an incentive to complex thinking (changing environment, hard-to-obtain food, strategic socialization, etc.).

Mammals
Mammals have some features that give them an advantage on other animal groups when it comes to intelligence: their metabolism is much faster than in every other group besides birds, they have a well developed brain, and their reproduction is based on a strong physical bond between mother and offspring, which makes easier the transmission of acquired knowledge through generations.

Primates
Of course, primates have very advanced cognitive abilities, especially apes: these include an extensive use of tools, complex comunication (mostly based on voice), traces of metacognition, a well-developed empathy and a remarkable ability in mind theory, which allows them to take part in a complex social structure with subtle political games of rivalries and alliances (except for orangutans, which are mostly solitary but not less intelligent). The most studied species among primates is the common chimpanzee, able to manipulate a wide range of tools - including rocks, sticks, branches, leaves - and to learn a great number of words to communicate through written pictograms (see here). Primates' prehensile hands are among the best manipulating organs in the animal kingdom. All the great apes, though, are highly endangered, and they probably won't produce other sapient species in the future.
 * Manipulators: grasping hands with opposable thumbs, prehensile tail in some species.
 * Feeding habits: omnivorous, almost continuous search of small quantities of food.
 * Society: very complex groups with (usually male) hierarchies and political alliances.
 * Typical EQ: 1.5 - 2.5

Cetaceans
Cetaceans notoriously include the living species with the second highest EQ after man - the bottlenose dolphin, with an astonishing EQ of 5.6. The cetacean brain has also a thick and rich neocortex, and in some of the larger dolphin species can weigh several kilograms. Their language, mostly based on high-frequency sounds that in some cases can travel for thousands of kilometres, can be very complex and culturally diversified (different populations of the same species "speak" different dialects . Baleen whales, living on an abundant and passive foodsource (krill and plankton) tend to be less intelligent than toothed whales, that actively hunt fish and seabirds.
 * Manipulators: none (dolphins hold objects with the snout).
 * Feeding habits: active aquatic hunters (toothed whales) or carnivorous filterers (baleen whales).
 * Society : solitary (most baleen whales) to small family groups; extensive offspring care.
 * Typical EQ: 0.5 - 2.5

Dolphins use specific calls as proper nouns, and take part both in highly coordinated hunt and in complex playing behaviours, such as producing bubble vortexes; though often violent and aggressive with other sea mammals or even other dolphins, they have a well-developed sense of empathy and they're able to recognise themselves in a mirror. Their largest fault with regard to intelligence is the lack of specialized manipulation organs, which greatly hinders tool-using abilities.

Elephants
The brain of an adult elephant can weigh up to 5 kg and has an extensive neocortex. Elephants are able to express a wide range of emotions and go through a particularly long childhood (up to 10 years long), which allows the effective teaching of learnt skills. Especially well-developed abilities include memory (they appear to suffer from PTSD), self-consciousness and empathy: the elephant brain, like the primate brains, contains a great number of mirror neurons (the brain cells that fire both when an individual performs an action and when it sees it performed by someone else, easing the identification between self and others); they also seem to have simple mathematical skills. Finally, elephants are the only non-human animals that maintain ritual behaviours associated with death. The muscular trunk is a good manipulation organ, though less versatile than a pair of hands.
 * Manipulators: a single boneless trunk, dexterous and versatile.
 * Feeding habits: constant browsing of low-energy leaves, grasses and bark.
 * Society: small matriarchal groups with calves, solitary males.
 * Typical EQ: 1.5

Canids
Dogs, and most of their close relatives, are by nature pack animals, and they have an extensive understanding of hierarchies and mutual obligations, something that could help developing the mind theory. They can easily be taught many specific and complex behaviours, though they often need to have an innate disposition, and they appear to be able to interpret human facial expressions. Still, most of these skills are a product of domestication, and they all partake in social behaviour, with little regard for problem solving. Wolves are not as responsive to study as dogs, but they seem to have a remarkable ability in connecting events (for example, recognising humans approaching from the noise of vehicles). Cooperative pack hunting of large preys stimulates simple strategic thought, which in turn can be a powerful source of cognitive development.
 * Manipulators: none (can only hold objects with the mouth).
 * Feeding habits: often hunt of large preys in packs, strategic behaviour.
 * Society: usually large packs, often territorial, with a hierarchical structure, complex communication.
 * Typical EQ: 1.0 - 1.5

Raccoons
Most studies on raccoon intelligence are over a century old, so they might not be very reliable today. According to a 1907 study, found them to be much more apt to problem-solving (specifically, escaping from puzzle-boxes) than cats or dogs, even on par with monkeys. Raccoons display a great curiosity about their environment and forage in a similar way to small primates; if they developed a more complex social structure they could get very close to monkeys in their behaviour.
 * Manipulators: grasping semi-prehensile hands.
 * Feeding habits: omnivorous, mostly plants and small preys.
 * Society: sometimes small groups of unrelated males or females, otherwise solitary.
 * Typical EQ: 1.5

Bears
Different bear species have a surprisingly high EQ, sometimes comparable to that of a monkey. Besides their great sensorial acuity, they have great navigational and food-finding skills and display a remarkable curiosity, on par with primates - the interest in exploring is a necessary step towards possible sapience. Their lifestyle is partially similar to that of apes, except for their solitary leanings. The largest bears, such as the grizzly and the polar bear, are not as smart as the smaller ones, while the giant panda - besides being endangered - feeds on plant matter extremely poor in energy. The best contestants for greater intelligence are the medium-sized, omnivorous species, especially the black bear (Ursus americanus): this seems to be able to distinguish different numbers.
 * Manipulators: can hold small objects with the paws.
 * Feeding habits: usually omnivorous, mostly plant matter, occasional hunt.
 * Society: mostly solitary, sometimes small groups of unrelated young individuals.
 * Typical EQ: 1.0 - 1.5

Pinnipeds
Seals, walruses and sealions are other animals with a remarkably high EQ, perhaps outcome of their active hunting lifestyle. The California sea lion (Zalophus californianus) Rio showed the ability to classify object in abstract categories, associating different pictures of animals according to similarity, or by transitivity (if A→B and B→C, then A→C) : this primitive logical skill is a prerequisite, and possibly a precursor, to true language; and also an excellent memory, remembering the categories after ten years. In a less stunning way, walruses can learn their calls to other individuals and modify them according to responses. Pinnipeds don't have manipulator organs, though many species still retain distinct fingers which could possibly be readapted for manipulation.
 * Manipulators: none.
 * Feeding habits: carnivorous, usually hunt of small aquatic animals.
 * Society: large undifferentiated groups, play behaviour.
 * Typical EQ: 1.0-1.5

Pigs
Wild pigs also have some features in common with primates: they form groups where each individual needs to keep track of others, and they forage often on a variety of foods. Though they don't recognise themselves in a mirror, they are able to use said mirror to find food hidden behind them, provided that they already was taught how it works. Pigs have a good memory, especially for food sources, and they can easily be trained. Anyway, they lack manipulation organs, though it's been suggested that their sensitive snout could evolve in an elephant-like trunk with the right selective pressure (for example, to strip branches of their leaves).
 * Manipulators: none.
 * Feeding habits: extremely omnivorous, mostly rooting in vegetation, rarely scavengers.
 * Society: matriarchal groups with common breeding, strong hierarchies from birth.
 * Typical EQ: 1.0

Birds
Birds have a metabolic activity similar to that of mammals (and sometimes even higher) and their neurons are more densely packed in the brain, allowing them to rival large mammals in intelligence with much smaller bodies. Some groups, including corvids and parrots, also show extensive offspring care, a prerequisite (and perhaps a cause?) to the development of a culture.

Parrots
Parrots have very similar to corvids regarding intelligence: several species have to practice it often for social interaction, and they display complex playing behaviour. The kea (Nestor notabilis) and the grey parrot (Psittacus erithacus) are especially curious and clever. In an experiment that compared keas with New Caledonian crows by allowing them to solve a puzzle in different ways, both with and without tools, keas experimented more freely with unfamiliar materials, and often solved the puzzle sooner than the crows, though they didn't show the same skill with the tools they used. The grey parrot Alex was successfully taught to use words to identify, count and describe objects, correctly answering questions such as "How many red squares?" . Having a short and curved beak, parrots cannot wield object with the same precision crows have, but they make up for this with their prehensile feet.
 * Manipulators: none specialized (they can hold tools with the beak and the feet).
 * Feeding habits: mostly herbivorous (seeds, fruit, nectar), rarely small preys.
 * Society: some solitary, some live in large flocks; prolonged offspring care.
 * Typical EQ: 1.5 - 2.0

Corvids
Most corvid species (crows, jays, ravens, magpies) have an EQ on par with elephants, great apes and dolphins, and their body-to-brain ratio is even higher than in humans (see the second table here). Crows, and especially the New Caledonian crow (Corvus moneduloides), are exceptionally innovative, being able to manipulate materials never seen before, use tools to safely examine potentially dangerous objects , and even using tools to obtain other tools. Newborn corvids are raised for a long period of time by different adults: this allows for an effective transmission of culture and learnt behaviours. Their greatest hindrance is, yet again, the lack of specialized manipulation organs, though the beak is somewhat useful to this end and the feet can also handle objects to some extent.
 * Manipulators: none specialized (they can hold tools with the beak and the feet).
 * Feeding habits: usually omnivorous, mostly small preys and plants.
 * Society: some solitary; some live in organized groups with a strong hierarchy; cooperative offspring care.
 * Typical EQ: 1.5

Reptiles
Reptiles are not usually as intelligent as birds or mammals: since they are mostly ectothermic (cold-blooded), they have a much lower consumption of energy; besides, their brain is generally much smaller and much less rich in structures and connections. Furthermore, they almost never look after their offspring after the hatch, and often even just after having laid the eggs. While no living reptile has specialized manipulation organs, some of them have prehensile tails (adaptations to live among the trees), while chameleons have feet with opposable toes. Still, there are rudiments of tool use: both crocodiles and alligators have been observed baiting birds with sticks (used in nest-building).

Still, there are many reptile species that manage to match and even outdo warm-blooded vertebrates in many areas. The Puerto Rican emerald anoles (Anolis evermanni) are able to solve new problems (reach food hidden under plastic covers), remember the solution for future use and adapt their techniques in different conditions (even faster than most birds and mammals). Tegus (Tupinambis sp.), large South American lizards, also show similar skills when they interact with humans; they have the largest brains of the reptilian world in terms of absolute mass, show cooperation and distinct personalities to each individual they are approached by.

Monitor lizards

 * Manipulators: a prehensile tail in arboreal species.
 * Feeding habits: mostly carnivores, a few omnivorous species.
 * Society: mostly solitary; sometimes cooperative hunting; almost no offspring care.
 * Typical EQ: less than 0.1

Despite their low EQ, these large lizards are among the most intelligent reptiles. Monitor lizards are able to, among other things, count up to six, distinguish distinct quantities and show engagement in play. Nile monitors (Varanus niloticus) have been observed hunting cooperatively, with one acting as a decoy to lure a crocodile away from her nest and then both return to feast on the eggs; Komodo dragons (Varanus komodoensis) can recognize different people; Varanus albigularis can quickly learn to obtain food from problem apparatuses.

Cephalopods
Cephalopods (members of the class of mollusks that comprises octopuses, squids and cuttlefish) are surprisingly intelligent, more than any other invertebrate: they have a mostly gangliar nervous system, but the main ganglia form a sort of central brain with very thick nervous fibres. Different species of squids, all active hunters, communicate effectively by rapidly changing colour, and the Humboldt squid (Dosidicus gigas) takes advantage of this ability to coordinate pack hunting. Octopuses manipulate a variety of tools with their boneless arms (among the best manipulating organs in the animal kingdom) : they can protect themselves with mollusks' and coconut shells, unscrew jars, pick up pebbles for future use (thus showing capacity of pianification).
 * Manipulators: several dexterous prehensile tentacles and arms.
 * Feeding habits: carnivorous (small preys on the seabottom).
 * Society: usually solitary; some squids live in groups or shoals; no offspring care.
 * Typical EQ: 1.0 - 1.5

Anyway, cephalopod intelligence seems to be very different from vertebrate intelligence. They show a lack of physiological emotional responses that would be unnatural for a vertebrate, and two thirds of an octopus' neurons are in its arms, making them partially independent from the brain. Furthermore, all cephalopods have a very brief lifespan: octopuses live alone, and they usually die right after reproducing, without tending to their offspring. When they do breed more than once, they live no more than five years.

Arthropods
Like cephalopods, arthropods have a gangliar nervous system, which limits greatly their chances to develop intelligence. Their body plan, based on an external skeleton with periodic moults and respiratory tracheae that directly connect the tissues with the outside, prevents them to become as big as vertebrates: the largest arthropod on Earth, the japanese spider crab, weighs up to 19 kg, while the largest land arthropod, the coconut crab, only weighs about 4 kg. In the Paleozoic era, when the air was richer in oxygen, the largest arthropods were the millipede-like Arthropleura on land and the sea-scorpion Jaekelopterus in the sea, both estimated to weigh up to 180 kg.

Jumping spiders
Spiders have concentrated part of their nervous system frontally, forming a sort of brain. Though they're usually ambush predators, the jumping spiders have adoptet a lifestyle as active hunters, and they coordinate their movements through a brain that reaches the 2% of the body mass (the same as ours). Those who hunt other spiders, such as Portia, can lure them by mimicking the movements of a prey trapped in the net; while their basic tactics are probably built on instinctive behaviours, Portia is believed to build upon these a learnt hunting strategy through trial-and-error.
 * Manipulators: none.
 * Feeding habits: active hunters, often baiting their prey.
 * Society: completely solitary.
 * Typical EQ: less than 0.1

Swarm intelligence
Decentralized, self-organizing systems can produce swarm intelligence, a emergent collective behaviour that allows to the group to "intelligently" interact with the environment, simply thanks to the interaction of a large number of members which act in a local and, to a certain extent, random way. In a way, individual intelligence is the swarm intelligence of many (in themselves unkthinking) neurons.

The features of collective intelligence are described here, as are those of a hypothetical "genetic sentience". On Earth, such a form of intelligence can be observed in swarming insects, schooling fish, flocking birds and herding mammals. When moving to a new nest, honeybees can collectively act on the information discovered by scouting individuals; travelling ant swarms choose the briefest path, singnaled with a self-renforcing trail of pheromons; bees, paper wasps, ants and termites build large and complex nests, sometimes with regular geometry, simply because the independent actions of each individual follow those of the others (stigmergy).

Not only swarms of social insects displar remarkable abilities of spatial orientation and problem-solving, but they also show traces of cultural lore: when the paths followed by ants around a nest are erased by winter, old ants remember them the following year and guide to younger ants, without having to discover anew the trails. Leaf-cutter ants even practice a simple form of agriculture, tending fungi that they feed with chewed leaves and protect from parasites.

Even slime molds, fungus-like colonies of single-celled protists, despite not having a nervous system at all and being able to sense the environment only through basic chemical cues, are surprisingly able to guide themselves through labyrinths, remembering past events and even predicting them. In an experiment in Japan (2010), the slime mold Physarum polycephalum was placed in a Petri plate with corn flakes arranged like the Tokyo subway stops (and flashing signals as obstacles). In 26 hours, extending tendrils and reabsorbing the less efficient ones, it reconstructed the subway map.

Examples in speculative biology

 * This discussion on the forum presents some intentionally unlikely sapients descended from terran animals, both as future evolution and alternate evolution, including sapient turtles, slugs, clams, horses and snakes.
 * A dicussion about alternate sapient sloths.
 * Ornosapien, future sapient descendant of parrots.