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How classification works

Capsule of the Day

FactSurgeryTreatment by physical intervention in the body. Surgery was limited for millennia not by knowledge of anatomy but by th…

New in the Library

  • FactTardigrade
  • FactMonarch Butterfly
  • FactSpider

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The library

Capsules

1,028 capsules, each one classified by the strength of its evidence.

All1,028Fact599Proven130Theory89Hypothesis71Contested90Debunked48
geography236biology88physics67history54medicine45astronomy33psychology26mathematics26chemistry20engineering20astrophysics19neuroscience19anthropology18art18

Trending now

Most recent activity

Facteconomics

Banking

Institutions that take deposits and make loans. The central fact about banking is that it creates money rather than merely storing it, and almost every difficulty the industry…

by Capsule · Aug 5, 2026
Factgeography

Selkirk

Selkirk is a city on the Red River about twenty-two kilometres northeast of Winnipeg, with 10,504 residents at the 2021 census. It came close to being the site of the…

by Capsule · Aug 7, 2026
Factbiology

Tardigrade

Tardigrades, also called water bears, are microscopic eight-legged animals forming their own phylum, Tardigrada, with around 1,500 described species. They are famous for surviving…

by Capsule · Aug 7, 2026
Fact

Browse all

Showing 441 to 460 of 1,028

NewestMost votedA to Z
Contested

The Hygiene Hypothesis

The hygiene hypothesis is the proposal that reduced exposure to microbes in early childhood leaves the immune system poorly calibrated, and that this…

byCapsule
biology

Salmon

Salmon are anadromous fish of the family Salmonidae: born in fresh water, grown at sea, and returning to fresh water to spawn, in most cases to the precise stream where they…

by Capsule · Aug 7, 2026
Factgeography

Thompson

Thompson is the largest city in northern Manitoba, roughly 650 kilometres north of Winnipeg on the Burntwood River, with 13,035 residents at the 2021 census. It was built from…

by Capsule · Aug 7, 2026
Factbiology

Monarch Butterfly

The monarch, Danaus plexippus, is a large orange and black butterfly of the Americas, and the migratory population of eastern North America performs a journey no individual…

by Capsule · Aug 7, 2026
Fact· Empirical

Selkirk

Selkirk is a city on the Red River about twenty-two kilometres northeast of Winnipeg, with 10,504 residents at the 2021 census. It came close to…

byCapsule0 votes0 reviewsAug 7, 2026
Fact· Empirical

Tardigrade

Tardigrades, also called water bears, are microscopic eight-legged animals forming their own phylum, Tardigrada, with around 1,500 described species.…

byCapsule0 votes0 reviewsAug 7, 2026

Also new

More from the last few days

biology
Fact· Empirical

Wolf

The grey wolf, Canis lupus, is the largest wild member of the dog family and once the most widely distributed land mammal on Earth after humans. It…

byCapsule0 votes0 reviews
economics
Fact

Accounting

The systematic recording and reporting of financial activity. Double-entry bookkeeping is among the more consequential inventions in the history of…

byCapsule0 votes0 reviews
medicine
Fact

Surgery

Treatment by physical intervention in the body. Surgery was limited for millennia not by knowledge of anatomy but by three specific obstacles, and…

byCapsule0 votes0 reviews
biology
Fact· Empirical

Sea Turtle

Sea turtles are marine reptiles of the superfamily Chelonioidea, seven living species that have been in the oceans for more than a hundred million…

byCapsule0 votes0 reviews
geography
Fact· Empirical

Portage la Prairie

Portage la Prairie is a city in central Manitoba on the Assiniboine River, about eighty kilometres west of Winnipeg, with 13,270 residents at the…

byCapsule0 votes0 reviews
biology
Fact· Empirical

Chimpanzee

The chimpanzee, Pan troglodytes, is one of the two species of the genus Pan and, with the bonobo, the closest living relative of human beings. It is…

byCapsule0 votes0 reviews
medicine
Fact

Nursing

The care of the sick, injured and dependent. Nursing is the largest health profession by a wide margin, its outcomes are measurable and substantial,…

byCapsule0 votes0 reviews
geography
Fact· Empirical

Flin Flon

Flin Flon is a mining city on the Manitoba and Saskatchewan boundary, about 630 kilometres northwest of Winnipeg, built directly on the rock of the…

byCapsule0 votes0 reviews

On this day

A birth or event with an anniversary today

history
Fact· Empirical

Statue of Liberty

The Statue of Liberty is a colossal copper statue on an island in New York Harbor, one of the most famous monuments in the United States and a…

byCapsule0 votes0 reviews

Settled science

Verified facts and proven results

See all
biology
Fact· Empirical

Octopus

Octopuses are eight-armed cephalopod molluscs, around three hundred species, found in every ocean. They have three hearts, blue blood, no skeleton,…

byCapsule0 votes0 reviews
history
Fact· Empirical

Great Wall of China

The Great Wall of China is not a single wall but a vast, discontinuous system of fortifications, walls, watchtowers, garrisons, and beacon towers,…

byCapsule0 votes0 reviews
agriculture
Fact

Traditional Yoruba Agricultural Practices in Southwestern Nigeria

The Yoruba people of southwestern Nigeria developed sophisticated agricultural systems over centuries that integrated intercropping, seasonal…

byCapsule0 votes0 reviews
biology
Fact· Empirical

Elephant

Elephants are the largest living land animals, and there are three species rather than the two most references still give. They have the longest…

byCapsule0 votes0 reviews
biology
Fact· Empirical

Great White Shark

The great white shark, Carcharodon carcharias, is the largest predatory fish, reaching about six metres. It is warm-blooded in a limited and…

byCapsule0 votes0 reviews
biology
Fact· Empirical

Lion

The lion, Panthera leo, is the only truly social cat and the second largest after the tiger. It once ranged from southern Africa through the Middle…

byCapsule0 votes0 reviews
agriculture
Fact

Nitrogen Cycling in Prairie Soils of the Canadian Prairies

Nitrogen cycling in Prairie soils is a well-documented biological and chemical process that determines agricultural productivity across Manitoba,…

byCapsule0 votes0 reviews
biology
Fact· Empirical

Penguin

Penguins are flightless seabirds of the southern hemisphere, around eighteen species, which gave up flight in the air for flight underwater. They are…

byCapsule0 votes0 reviews
physics
Fact

Gravity

Gravity is the universal attractive interaction between masses, described at low energy by Newton's law of universal gravitation and at all energies…

byCapsule0 votes0 reviews
geography
Fact· Empirical

Amazon Rainforest

The Amazon Rainforest is the largest tropical rainforest on Earth, a vast sea of green covering some 5.5 million square kilometres across nine South…

byCapsule0 votes0 reviews
astronomy
Fact· Empirical

The Moon

The Moon is Earth's only natural satellite and the brightest object in our night sky. Large in proportion to its planet and close enough to study…

byCapsule0 votes0 reviews
biology
Fact· Empirical

Domestic Cat

The domestic cat, Felis catus, is the most numerous small carnivore on Earth, with something over six hundred million individuals. It is also barely…

byCapsule0 votes0 reviews

Open questions

Hypotheses under investigation and ideas still debated

See all
engineering
Contested

Renewable Energy and Electrical Grid Stability

Wind and solar generation are non-dispatchable and produce zero rotational inertia, raising legitimate concerns about frequency regulation and…

byCapsule0 votes0 reviews
earth science
Hypothesis

The Gaia Hypothesis

The Gaia hypothesis proposes that life and its physical environment on Earth form a single, self regulating system that keeps the planet suitable for…

byCapsule0 votes0 reviews
psychology
Hypothesis

Social Media Use and Adolescent Depression: Causal Relationship Under Investigation

The proposition that social media use directly causes depression in adolescents remains under active scientific investigation. While correlational…

byCapsule0 votes0 reviews
history
Contested

The Bronze Age Collapse

The Bronze Age collapse was a sudden, widespread breakdown of civilizations around the eastern Mediterranean roughly 3,200 years ago. Within a few…

byCapsule0 votes0 reviews
astronomy
Hypothesis

Planet Nine

Planet Nine is a hypothetical large planet proposed to exist in the far outer reaches of our Solar System, well beyond Neptune and Pluto. It has…

byCapsule0 votes0 reviews
physics
Hypothesis

Wormholes

A wormhole is a hypothetical tunnel through spacetime that could, in principle, connect two distant points in the universe, or even two different…

byCapsule0 votes0 reviews
earth science
Contested

What Causes the Ice Ages

Throughout its history, the Earth has repeatedly cooled into ice ages, when vast sheets of ice spread across the continents, and warmed again between…

byCapsule0 votes0 reviews
astronomy
Contested

Is Pluto a Planet?

Whether Pluto should be called a planet is a question that has divided astronomers and captured the public imagination. Discovered in 1930 and…

byCapsule0 votes0 reviews
biology
Contested

Are Animals Conscious?

Whether animals have conscious experiences, an inner life of feelings and awareness, is a deep and genuinely contested question. That many animals…

byCapsule0 votes0 reviews
biology
Hypothesis

Abiogenesis: The Origin of Life

Abiogenesis is the natural process by which life is thought to have arisen from non living matter, such as simple chemical compounds. How life first…

byCapsule0 votes0 reviews
psychology
Contested

The Origin of Language

How human language first arose is one of the hardest questions in science. That we alone among animals possess full language is clear; when, how, and…

byCapsule0 votes0 reviews
science
Hypothesis

Quantum Entanglement as a Substrate for Consciousness

The hypothesis proposes that quantum entanglement between microtubule subunits inside neurons could provide a physical substrate for unified…

byCapsule0 votes0 reviews

Debunked

Claims the evidence overturned

See all
physics
Debunked

Perpetual Motion

Perpetual motion is the idea of a machine that runs forever without any energy source, or that produces more energy than it consumes. Inventors have…

byCapsule0 votes0 reviews
history
Debunked

Piltdown Man

Piltdown Man was a supposed "missing link" between apes and humans, announced in 1912 from fossil fragments found in England. For decades it misled…

byCapsule0 votes0 reviews
neuroscience
Debunked

The Left-Brain, Right-Brain Myth

The idea that people are left-brained and therefore logical, or right-brained and therefore creative, is one of the most widely believed claims about…

byCapsule0 votes0 reviews
medicine
Debunked

Humorism: The Four Humors

Humorism, or humoral theory, was the belief that human health depends on the balance of four bodily fluids, called humors: blood, phlegm, yellow…

byCapsule0 votes0 reviews
history
Debunked

Astrology

Astrology is the belief that the positions of the Sun, Moon, planets, and stars influence human affairs and personalities, and that they can be used…

byCapsule0 votes0 reviews
criminology
Debunked

Criminal Profiling

Offender profiling infers a perpetrator's characteristics from crime scene evidence. The specific claim that it reliably narrows a suspect pool, and…

byCapsule0 votes0 reviews
astronomy
Debunked

The Martian Canals

The Martian canals were a network of fine, straight lines that some astronomers in the late nineteenth and early twentieth centuries believed they…

byCapsule0 votes0 reviews
science
Debunked

Cold Fusion at Room Temperature

The 1989 Fleischmann-Pons announcement claimed that palladium electrodes immersed in heavy water produced excess heat consistent with…

byCapsule0 votes0 reviews
medicine
Debunked

Do Vaccines Cause Autism?

The claim that vaccines cause autism is one of the most damaging medical myths of modern times. It has been investigated exhaustively and thoroughly…

byCapsule0 votes0 reviews
astronomy
Debunked

Flat Earth

The idea that the Earth is flat is a debunked belief that the planet is a disc or a plane rather than a sphere. It has been contradicted by…

byCapsule0 votes0 reviews
biology
Debunked

Spontaneous Generation

Spontaneous generation was the long held belief that living organisms could arise directly from non living matter. People thought maggots formed from…

byCapsule0 votes0 reviews
astrophysics
Debunked

The Steady State Theory

The steady state theory was a model of the universe, popular in the mid twentieth century, which held that the universe has always looked roughly the…

byCapsule0 votes0 reviews

Theories explained

Well substantiated explanations of how things work

See all
biology
Theory

Mendelian Inheritance

Mendelian inheritance is the set of principles describing how traits are passed from parents to offspring through discrete units we now call genes.…

byCapsule0 votes0 reviews
physics
Theory· Scientific

General Relativity

General relativity is Albert Einstein's theory of gravity, published in 1915. It reimagines gravity not as a force pulling objects together but as…

byCapsule0 votes0 reviews
mathematics
Theory

Set Theory

Set theory is the branch of mathematics that studies collections of objects, called sets. Though it begins with an idea as simple as grouping things…

byCapsule0 votes0 reviews
mathematics
Theory

Topology

Topology is the branch of mathematics that studies the properties of shapes that survive stretching, bending, and twisting, but not tearing or…

byCapsule0 votes0 reviews
biology
Theory

Endosymbiotic Theory

Endosymbiotic theory explains the origin of the complex cells that make up plants, animals, fungi, and other higher organisms. It proposes that key…

byCapsule0 votes0 reviews
physics
Theory

Aerodynamics: How Flight Works

Aerodynamics is the study of how air flows around objects and the forces this creates. It is the science that explains how aircraft fly, how cars and…

byCapsule0 votes0 reviews
earth science
Theory· Scientific

Plate Tectonics

Plate tectonics is the scientific theory that Earth's outer shell is broken into a set of large, rigid plates that drift slowly over the hotter,…

byCapsule0 votes0 reviews
earth science
Theory

The Greenhouse Effect

The greenhouse effect is the process by which certain gases in a planet's atmosphere trap heat, keeping the surface warmer than it would otherwise…

byCapsule0 votes0 reviews
mathematics
Theory

The Theory of Computation

The theory of computation is the branch of mathematics and computer science that asks what problems can be solved by computation, and how…

byCapsule0 votes0 reviews
medicine
Theory· Scientific

Germ Theory of Disease

The germ theory of disease is the scientific theory that many illnesses are caused by microorganisms, living agents too small to see, that invade the…

byCapsule0 votes0 reviews
physics
Theory· Emerging

String Theory

String theory is a theoretical framework that attempts to unify all the forces and particles of nature, including gravity, into a single description.…

byCapsule0 votes0 reviews
computer science
Theory· Mathematical

Information Theory

Information theory is the mathematical study of how information is measured, stored, and communicated. It defines what information actually is in…

byCapsule0 votes0 reviews
0 votes0 reviews
Aug 3, 2026
Theory· Scientific

Autoimmunity

Autoimmunity is the immune system attacking the body it belongs to. Around a hundred distinct autoimmune conditions are recognised, together…

byCapsule0 votes0 reviewsAug 3, 2026
Theory

Herd Immunity

Herd immunity is the protection an unvaccinated person receives when enough of the people around them are immune that a chain of transmission cannot…

byCapsule0 votes0 reviewsAug 3, 2026
Contested

Climate Tipping Points

A climate tipping point is a threshold beyond which part of the Earth system shifts into a different state, and does not shift back when the forcing…

byCapsule0 votes0 reviewsAug 3, 2026
Theory· Scientific

Extreme Event Attribution

Extreme event attribution is the field that answers the question people ask after every flood, heatwave, and storm: did climate change cause this?…

byCapsule0 votes0 reviewsAug 3, 2026
Contested

Climate Sensitivity

Climate sensitivity is the amount of warming that follows from doubling the concentration of carbon dioxide in the atmosphere. It is the single…

byCapsule0 votes0 reviewsAug 3, 2026
Theory· Scientific

Horizontal Gene Transfer

Horizontal gene transfer is the movement of genetic material between organisms by means other than parent to offspring. It is ordinary among…

byCapsule0 votes0 reviewsAug 3, 2026
Contested

The Heritability of Intelligence

How much of the variation in measured intelligence is attributable to genetic variation is among the most technically misunderstood questions in…

byCapsule0 votes0 reviewsAug 3, 2026
Contested

Junk DNA

Only a small fraction of the human genome codes for proteins, something under two per cent. What the rest of it is doing has been argued about for…

byCapsule0 votes0 reviewsAug 3, 2026
Proven· Replicated

CRISPR Gene Editing

CRISPR is a method for cutting DNA at a chosen location, which makes editing a genome a routine laboratory procedure rather than a specialist feat.…

byCapsule0 votes0 reviewsAug 3, 2026
Theory· Scientific

Epigenetics

Epigenetics is the study of changes in how genes are used that do not involve changes to the DNA sequence itself. Every cell in a body carries the…

byCapsule0 votes0 reviewsAug 3, 2026
Theory

Stratigraphy

Stratigraphy is the study of layers, and the principle that where deposits lie undisturbed the lower ones were laid down before the upper ones. It…

byCapsule0 votes0 reviewsAug 3, 2026
Contested

The Indus Script

The Indus Valley Civilisation left behind thousands of inscribed objects, mostly small stone seals, carrying sequences of signs that nobody can read.…

byCapsule0 votes0 reviewsAug 3, 2026
Contested

Gobekli Tepe

Gobekli Tepe is a complex of monumental stone enclosures in southeastern Turkey, built around eleven thousand years ago by people who had not yet…

byCapsule0 votes0 reviewsAug 3, 2026
Proven· Replicated

Radiocarbon Dating

Radiocarbon dating measures how much carbon-14 remains in something that was once alive, and converts that into an age. Developed by Willard Libby in…

byCapsule0 votes0 reviewsAug 3, 2026
Contested

Dunbar's Number

Dunbar's number is the proposal that humans can maintain roughly 150 stable social relationships, and that the limit is set by the size of the brain.…

byCapsule0 votes0 reviewsAug 3, 2026
Theory

Kinship Systems

Kinship is the study of how societies organise relatedness, and it was for a long time the central preoccupation of anthropology. The finding that…

byCapsule0 votes0 reviewsAug 3, 2026
Contested

Cultural Relativism

Cultural relativism is the principle that a culture should be understood on its own terms rather than judged against the standards of another. It…

byCapsule0 votes0 reviewsAug 3, 2026
Theory

Anomie

Anomie is the condition of a society whose norms have weakened or become unclear, leaving individuals without adequate guidance about what to want or…

byCapsule0 votes0 reviewsAug 3, 2026
Contested

The Protestant Ethic Thesis

In 1905 Max Weber argued that the Protestant Reformation, and Calvinism in particular, produced a cultural disposition toward disciplined work and…

byCapsule0 votes0 reviewsAug 3, 2026
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