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333 entries
The universe has an age
The observable universe is 13.8 billion years old, measured from the cosmic microwave background under ΛCDM.
Nothing outruns light in vacuum
The speed of light in vacuum is invariant, and since 1983 it is defined as exactly 299,792,458 metres per second.
Black holes are real
Spacetime can curve so steeply that light cannot escape. Mergers of such objects have been heard in gravitational waves and imaged in radio light.
The sky still glows from its first light
A nearly isotropic microwave background of 2.725 K fills the sky and is the leftover radiation from recombination.
Every cell on Earth is kin
All known terrestrial life shares a common ancestor. The evidence is a nested hierarchy of traits plus a shared genetic code.
Heredity is a molecule
DNA is the hereditary material of cellular life. Its double helix stores sequence information that is replicated and transcribed.
Selection writes the fit
Heritable variation plus differential reproduction produces adaptation. This is natural selection.
Memory is a reconstruction
Human episodic memory is not a recording. It is rebuilt at recall and can be systematically distorted.
Judgment has a shape
Human judgment departs from normative logic and probability in systematic, replicable ways — not as random error.
Thought has a narrow desk
Working memory holds only a few items at once — on the order of four chunks in typical adults, not an inner theatre of unlimited space.
Writing is five thousand years old
True writing — a system that can record language, not only tallies — appears in southern Mesopotamia around 3200 BCE.
Farming began after the ice
The first durable agricultural economies appear in the Fertile Crescent about 11,500 years ago, after the last glacial period.
Half of us eat from the air
Industrial ammonia synthesis (Haber–Bosch) now supplies the reactive nitrogen for roughly half of the protein in the global diet.
Atoms are almost empty
An atom’s mass sits in a tiny nucleus. The rest of its volume is a cloud of electrons; ordinary matter is mostly void.
Entropy does not volunteer to fall
In a closed system, entropy does not decrease. Useful energy dissipates. This is the second law of thermodynamics.
The ground moves
Earth’s lithosphere is broken into plates that move over the mantle. Continents drift, seafloor spreads, and mountains rise at the boundaries.
Clocks disagree on purpose
GPS satellite clocks run faster than identical clocks on Earth’s surface by about 38 microseconds per day, as general and special relativity predict. The system corrects for it or it fails.
Rocks keep time by decay
Radioactive isotopes decay at measured rates. Isochron and concordia methods date rocks from thousands to billions of years.
The future is the higher-entropy direction
The thermodynamic arrow of time — why we remember the past and not the future — is the universe’s low-entropy beginning plus the second law.
A living language keeps an old grammar
Lithuanian is among the most conservative living Indo-European languages, retaining archaic phonology and morphology that illuminate the parent tongue.
You are transparent to most of the sun
Hundreds of trillions of solar neutrinos pass through your body every second, and almost none of them hit anything.
The sun is losing millions of tonnes a second
Sunlight is mass. Fusion converts about four million tonnes of the sun into energy every second, and a solar wind carries still more away.
The universe is wider than its age allows
The observable universe is about 93 billion light-years across, even though it is only 13.8 billion years old.
Saturn would float
Saturn’s mean density is about 0.69 grams per cubic centimetre, less than liquid water.
A teaspoon can outweigh a mountain
Neutron-star matter has a density around that of an atomic nucleus. A teaspoon of it would have a mass of order a billion tonnes.
The moon is leaving
Lunar laser ranging shows the Moon receding from Earth by about 3.8 centimetres a year.
The hottest planet’s neighbour keeps ice
Mercury, closest planet to the sun, holds water ice in craters at its poles that sunlight never enters.
There are lakes that are not water
Saturn’s moon Titan has stable lakes and seas of liquid methane and ethane, mapped by Cassini and landed on by Huygens.
An ocean hides under the ice
Saturn’s small moon Enceladus vents salt water from a subsurface ocean, sampled in flight by Cassini.
Giant planets can orbit in days
Planets with the mass of Jupiter orbit some stars in a few days, far inside the distance at which they were expected to form.
Antimatter falls down
Antihydrogen, released in a magnetic trap, accelerates downward under Earth’s gravity, as ordinary hydrogen does.
Gravity keeps the same speed as light
The neutron-star merger GW170817 and its gamma-ray burst arrived within about two seconds after 130 million years of travel. Gravity and light share a speed.
Neutrinos change costume in flight
A neutrino born as one flavor — electron, muon, or tau — can be detected as another. The change requires that neutrinos have mass.
A day on Venus outlasts its year
Venus takes 243 Earth days to spin once relative to the stars, and only 225 Earth days to orbit the sun.
Dead stars keep better time than watches
Pulsars are rotating neutron stars. Their radio beams sweep like a lighthouse, some of them with a stability that rivals atomic clocks.
The bricks of protein fall from the sky
The Murchison meteorite, a carbonaceous chondrite that fell in 1969, contains amino acids that formed in space, not in Earth soil.
A tree is built mostly from air
The dry mass of a tree is chiefly cellulose and lignin made from carbon dioxide. The carbon came out of the atmosphere, not out of the soil.
Sharks were swimming before trees stood
Shark-like fishes appear in the fossil record before the earliest trees. Teeth and scales of chondrichthyans predate Archaeopteris.
Birds are dinosaurs
Birds sit inside Dinosauria. They are the living continuation of theropod dinosaurs, not a neighbouring class that merely resembles them.
The whale’s closest living cousin is the hippo
Molecular phylogeny places whales inside the even-toed ungulates, with hippos as their nearest living relatives.
Your mitochondria used to be free
Mitochondria descend from bacteria that took up residence inside another cell. They still carry their own circular genome.
Ants invented farming long before we did
Leafcutter ants grow a fungus on harvested leaves and have done so for tens of millions of years. The fungus is their crop.
A slime can solve a maze
The plasmodium of Physarum polycephalum finds the shortest path through a maze by growing toward food and letting dead ends starve.
Some animals survive the vacuum
Tardigrades in a dried tun state have survived exposure to open space on a satellite, including vacuum and, with some shielding, solar ultraviolet.
Wombat dung is a cube
Bare-nosed wombats produce roughly cubic feces. The corners are formed by a stiff intestine of uneven elasticity, not by a square hole.
A shrimp punch boils the water
The peacock mantis shrimp’s club strike is so fast it cavitates seawater. The bubble collapses and adds a second blow, with a brief temperature of thousands of degrees.
A snap in the ocean is briefly as hot as the sun
The pistol shrimp’s claw collapses a cavitation bubble that reaches about 5,000 K and emits a flash and a crack louder than a gunshot.
A jellyfish can age backwards
Turritopsis dohrnii can revert from a free-swimming medusa to a juvenile polyp, rewriting its life cycle instead of dying after spawning.
A shark can be older than a nation
Eye-lens radiocarbon dates Greenland sharks at lifespans of centuries. One large female was estimated at about 400 years, with a wide uncertainty.
A bird flies an ocean without landing
Satellite-tracked bar-tailed godwits fly nonstop from Alaska to New Zealand, more than 11,000 kilometres, in about eight or nine days.
Some birds sleep while flying
Great frigatebirds sleep in flight, mostly with one hemisphere at a time, for minutes at a stretch, on trips that last weeks.
Bees tell each other where the flowers are
A honey bee’s waggle dance encodes the direction and distance of food. Other bees read it in the dark and fly the route.
A cat cannot taste sugar
Cats lack a working sweet receptor. The Tas1r2 gene that encodes one half of it is a pseudogene in all felids tested.
Every clownfish starts as male
Clownfish are protandrous hermaphrodites. Juveniles mature as males. The dominant fish in a group becomes the female.
A dragon can reproduce alone
Female Komodo dragons can produce viable offspring by parthenogenesis. It has been documented in zoos in females kept without males.
Most of an octopus thinks in its arms
About two thirds of an octopus’s neurons are in the arms, not the central brain. Each arm can organise reaching and touch locally.
Some blood runs blue
Octopuses, horseshoe crabs, and many other animals carry oxygen with copper-based hemocyanin. Oxygenated, it is blue.
Almost none of your genome is genes
About one to two percent of the human genome codes for proteins. The rest is regulatory sequence, introns, and a great deal of repeats.
You cannot tickle yourself
A self-produced touch is cancelled by a prediction from the cerebellum. The same touch from someone else is not, and it tickles.
There is a hole in your vision
Each eye has a blind spot where the optic nerve leaves the retina. There are no photoreceptors there. You do not see the hole.
You go blind every time you look around
During a saccade — the jump of the eye from one point to another — vision is suppressed. You do not see the smear the motion would produce.
A gorilla can cross the room unseen
When attention is spent on a demanding visual task, a person in a gorilla suit can walk through the scene and about half of viewers do not report it.
What you hear depends on what you see
A voice saying “ba”, dubbed onto a face mouthing “ga”, is often heard as “da”. The syllable is a compromise the brain invented.
Some blind people can point at what they cannot see
After damage to the primary visual cortex, some patients report no sight in part of the field and still discriminate location or motion there above chance.
A human eye can catch one photon
Dark-adapted people can detect a single photon in a laboratory, above chance, and their confidence tracks the trials where the photon was actually sent.
You glow, too faintly to see
The human body emits a steady trickle of visible photons, brightest in the late afternoon and strongest on the face. The light is real and far below vision.
Swearing raises the pain threshold
People who repeat a swear word keep a hand in ice water longer than people who repeat a neutral word.
A sugar pill can change the body
Placebo analgesia is partly opioid. A drug that blocks opioid receptors also blocks some of the pain relief of a sham treatment.
Coffee does not give you energy
Caffeine keeps you alert by blocking adenosine receptors. It does not supply energy to the brain. It hides the signal that you have been awake.
Rats laugh when they are tickled
Rats emit ultrasonic chirps near 50 kilohertz during play and tickling. The calls track reward and approach.
Your nostrils take turns
In most people the two sides of the nose alternate congestion across a few hours. One side leads, then the other.
Cold water on the face slows the heart
Submerging the face in cold water, while holding the breath, triggers the mammalian dive reflex: heart rate falls and blood shifts toward the chest.
Cleopatra lived closer to us than to the pyramids
Cleopatra died in 30 BCE. The Great Pyramid was finished about 2,500 years before that. The Moon landing was about 2,000 years after.
Oxford is older than the Aztec Empire
Teaching at Oxford is recorded from 1096. The Aztec Empire, as a triple alliance, was founded in 1428.
The oldest complaint we have is about bad copper
A clay tablet from Ur, about 1750 BCE, records a customer named Nanni berating the merchant Ea-nasir for sending low-grade copper.
The Greeks built a computer
The Antikythera mechanism is a geared device from the second or first century BCE that computed calendars and the positions of the Sun and Moon.
The size of the Earth was known in antiquity
Eratosthenes, in the third century BCE, measured Earth’s circumference from the angle of the Sun at two cities and the distance between them.
Roman concrete heals itself
Ancient Roman marine concrete contains lime clasts that dissolve into cracks and recrystallise, sealing them. The process has been reproduced.
A war lasted about thirty-eight minutes
The Anglo-Zanzibar War, on 27 August 1896, ran from roughly 9:02 to 9:40 in the morning. It is the shortest war on record.
Towns are older than the wheel
Permanent settlements such as Jericho were inhabited thousands of years before the first wheeled vehicles, which appear around 3500 BCE.
Chess is larger than the observable universe
The number of possible chess games is on the order of 10 to the 120. The number of atoms in the observable universe is on the order of 10 to the 80.
A spoken language was brought back from books
Hebrew, used for scripture and scholarship for centuries, was rebuilt as a daily spoken language in the late nineteenth and early twentieth centuries.
Crystals can be impossible
Quasicrystals show sharp diffraction and a symmetry — including five-fold — that classical crystallography had proved a repeating lattice cannot have.
Absolute zero cannot be reached
The third law of thermodynamics implies that no finite sequence of steps can cool a system to absolute zero.
Helium refuses to freeze
Helium-4 at ordinary pressure stays liquid down to absolute zero. It does not become a solid unless the pressure exceeds about 25 atmospheres.
Liquid helium climbs out of its cup
Below 2.17 kelvin, helium-4 becomes a superfluid and creeps as a thin film up and over the walls of an open container.
Lakes freeze from the top because water is heaviest at 4 °C
Liquid water reaches its maximum density at about 4 °C. Colder water floats, so a lake loses heat at the surface and ice forms there, insulating the life below.
Lightning is hotter than the surface of the sun
A lightning return stroke heats its channel to about 30,000 kelvin. The Sun’s photosphere is about 5,800 kelvin.
A proton is heavier than its parts
The quarks inside a proton account for only about one percent of its mass. The rest is the energy of the gluon field and the motion of the quarks, via E = mc².
The sun runs on a reaction that is classically forbidden
Proton fusion in the sun requires quantum tunnelling. At solar-core temperatures the protons do not have the energy to cross their mutual electric repulsion.
A phone remembers by breaking a rule
Flash memory stores bits by letting electrons tunnel onto an isolated conductor. They should not be able to cross the insulator. A thin enough insulator is not a veto.
Atoms can be seen
A scanning tunnelling microscope images individual atoms by measuring a tunnelling current between a sharp tip and a surface.
A cloud of atoms can become one wave
In a Bose–Einstein condensate, thousands of atoms occupy the same quantum state and behave as a single matter wave. It was made in a gas in 1995.
The floor holds you up by a rule about electrons
You do not fall through the floor because the Pauli exclusion principle keeps electrons from all occupying the same low-energy state. Electrostatic charge is not the whole story.
A sheet of carbon can be one atom thick
Graphene is a single layer of carbon atoms in a honeycomb. It is strong, an excellent conductor, and it was isolated with adhesive tape.
A magnet will float above a cold metal
A superconductor expels magnetic fields. A magnet placed over it levitates, held by the currents the field itself induces.
Entanglement does not send a message
Entangled particles show correlations that no local classical story can match. Those correlations cannot be used to send information faster than light.
Empty space can pull two plates together
The Casimir effect is an attractive force between two uncharged metal plates in a vacuum, caused by the way the plates change the quantum field between them.
You are radioactive
A typical adult body contains enough potassium-40 and carbon-14 to undergo several thousand nuclear decays every second.
Hospitals use antimatter
A PET scan detects pairs of gamma rays produced when positrons — antielectrons — annihilate with electrons in the body.
A day is not 24 hours
Relative to the stars, Earth rotates once in 23 hours, 56 minutes, and about 4 seconds. The 24-hour day is noon to noon, which includes the orbit.
Coral kept the time of ancient days
Growth bands in Devonian corals show about 400 days in a year. The year had more days because each day was shorter.
You are moving thirty kilometres a second
Earth orbits the sun at about 29.8 kilometres per second. Sitting still is a description of the chair, not of the ride.
A particle lives longer because it is moving
Cosmic-ray muons reach the ground in numbers that only make sense if their clocks run slow. Their half-life in flight matches special relativity.
The second is a number of wiggles
Since 1967 the second has been defined as 9,192,631,770 periods of the radiation from a particular transition in caesium-133.
Andromeda is coming
The Andromeda galaxy is moving toward the Milky Way at about 110 kilometres per second. A collision in roughly four to five billion years follows from that velocity.
There is no universal now
In special relativity, whether two distant events are simultaneous depends on the motion of the observer. Nature does not supply one shared present.
The ground at the equator is moving at 1,670 kilometres an hour
Earth’s equatorial circumference and its sidereal day give a ground speed of about 1,670 km/h. A point near the pole barely moves.
The day is getting longer
Tidal friction slows Earth’s spin. The length of the day increases by a few milliseconds per century, measured with ancient eclipses and with lasers.
A year does not divide into days
The tropical year is about 365.2422 days. The fraction is why the calendar needs leap days, and why no integer calendar stays honest forever.
The Earth is not a sphere
Earth is an oblate spheroid. The equatorial radius is about 21 kilometres longer than the polar radius.
Antarctica is a desert
The interior of Antarctica receives so little precipitation that it is the largest desert on Earth.
The Sahara was green
Between about 11,000 and 5,000 years ago the Sahara held lakes, grasslands, and people.
A lake sits under four kilometres of ice
Lake Vostok, in East Antarctica, is a liquid freshwater lake about 250 kilometres long, sealed under roughly four kilometres of ice.
The longest mountain chain is underwater
The mid-ocean ridge system runs about 65,000 kilometres, longer than the Andes and the Rockies combined, and almost all of it is submerged.
A lake emptied across a province
Near the end of the last ice age, glacial Lake Missoula burst repeatedly and sent floods across what is now eastern Washington, carving the Channeled Scablands.
The Earth rings after a great earthquake
A very large earthquake sets the whole planet into free oscillation. The tones can be recorded for days.
Most fresh water is ice
About two thirds of the fresh water on Earth is locked in ice sheets and glaciers, and almost all of that ice is in Antarctica.
A cloud weighs hundreds of tonnes
A modest fair-weather cumulus, about a kilometre on a side, holds on the order of a few hundred tonnes of liquid water.
Raindrops are not tears
Small raindrops are spheres. Large ones are flattened on the bottom, like hamburger buns. None of them are teardrops.
Some dunes sing
Certain dry sand dunes emit a loud, sustained low note when sand avalanches down their slip face.
Some lightning never comes down
Above large thunderstorms the upper atmosphere flashes upward: red sprites, blue jets, and elves, kilometres above the cloud tops.
A volcano cancelled a summer
The April 1815 eruption of Tambora cooled the planet enough that 1816 was, in many places, the year without a summer.
Some rivers never find the sea
In an endorheic basin, rivers end in a lake or a salt flat. The Okavango dies in a delta in the Kalahari and does not reach an ocean.
The blood in your veins is not blue
Venous blood is dark red. Veins look blue through the skin because of how tissue scatters light, not because the blood changed colour.
You are taller before breakfast
Most adults lose about a centimetre of height between morning and night, as the spinal discs compress, and regain it lying down.
Half your bones are in the hands and feet
A typical adult skeleton has 206 bones. Fifty-four are in the hands and fifty-two in the feet, just over half the total.
The stomach is a vat of acid
Resting gastric juice has a pH around 1.5 to 3.5, in the range of battery acid, strong enough to denature protein.
The liver grows back
After a large part of a healthy liver is removed, the remnant regrows toward the original mass.
You are not outnumbered ten to one
Bacterial cells in the body and human cells are in the same order of magnitude. The famous ten-to-one ratio was an overestimate.
You can see your own blood cells
Against a clear blue sky, many people see tiny bright dots darting on short paths. Those are white blood cells moving through capillaries in the retina.
A baby has more bones than an adult
A newborn skeleton has on the order of 300 bony elements. Many fuse, so a typical adult has 206.
Adults still have a furnace of brown fat
Adult humans keep deposits of brown adipose tissue that burn fuel to make heat when the body is cold.
Most of your serotonin is not in your brain
About ninety percent of the body's serotonin is made in the gut, largely by enterochromaffin cells.
The window of the eye has no blood
The cornea has no blood vessels. It takes much of its oxygen from the air, through the tear film.
A human egg can be seen without a microscope
A human oocyte is about a tenth of a millimetre across, just large enough to see as a speck in good light.
The marrow replaces the blood without pause
A typical adult produces on the order of two million red blood cells every second to replace those that are retired.
Flavour is mostly smell
What is called flavour is largely retronasal smell — odorants from the mouth reaching the nose — together with taste, touch, and temperature.
A mushroom is closer to you than to a rose
Fungi share a more recent common ancestor with animals than either does with plants.
The largest organism is a fungus
A single honey fungus in Oregon, Armillaria ostoyae, occupies on the order of ten square kilometres of forest floor.
A frog freezes and then walks away
The wood frog spends northern winters frozen. Its heart stops, ice forms between its cells, and in spring it thaws and moves.
A living tree is older than the pyramids
At least one Great Basin bristlecone pine alive today germinated before the Great Pyramid was built.
The ocean holds more viruses than the sky holds stars
A standard estimate puts on the order of 10 to the 30 virus particles in the oceans. The observable universe holds on the order of 10 to the 22 or 10 to the 24 stars.
Half of photosynthesis happens in the water
About half of Earth's net primary production — the carbon fixed by photosynthesis — takes place in the ocean.
The platypus lays eggs, makes milk, and carries venom
The platypus is a mammal that lays eggs, feeds its young on milk secreted through the skin, and, in the male, has a venomous spur.
The father gives birth
In seahorses, the male carries the pregnancy. The female deposits eggs in his brood pouch, and he bears them until they are born.
A fish returned from the fossil record
The coelacanth was known as a Cretaceous fossil until a living one was caught off South Africa in 1938. A second species was later found in Indonesia.
A polar bear is not white
The hairs of a polar bear are unpigmented and translucent. The skin underneath is black. The coat looks white because the hairs scatter visible light.
An octopus keeps three hearts
Two branchial hearts pump blood through the gills. A third, the systemic heart, pumps it through the body. During jet swimming the systemic heart pauses.
A beetle fires a boiling spray
The bombardier beetle mixes reactants in a reaction chamber and ejects a pulsed spray of hot quinones, near the boiling point of water.
Almost none of the universe is made of atoms
In the standard cosmological model, ordinary atomic matter is about five percent of the universe. The rest is dark matter and dark energy.
There are more trees on Earth than stars in the galaxy
A 2015 census estimated about three trillion trees on Earth. The Milky Way contains on the order of one to four hundred billion stars.
The stars you can see are still there
Light from the bright naked-eye stars has usually been traveling for decades to a few thousand years. Those stars live for millions to billions of years. Almost none of them have died while the light was in flight.
A black hole can be less dense than air
If density means mass divided by the volume inside the event horizon, then a sufficiently massive black hole is less dense than water, and a still larger one is less dense than air.
A day on Mercury lasts two years
Mercury orbits the Sun in about 88 Earth days. Sunrise to sunrise on Mercury takes about 176 Earth days, which is two of its years.
Saturn's rings are thinner than a city
The main rings span hundreds of thousands of kilometres and are, over much of their extent, only tens of metres thick.
The Sun is white
Above the atmosphere the Sun's light is white. It looks yellow or red from the ground because air scatters the blue end of its spectrum.
The perfect eclipse is a coincidence of this era
The Sun is about 400 times wider than the Moon and about 400 times farther away, so their discs nearly match. Total solar eclipses are a temporary accident.
A storm on Jupiter is larger than the Earth
The Great Red Spot is an anticyclone observed for more than a century and a half, and for most of that time its long axis has been larger than Earth's diameter.
We have made places colder than space
The cosmic microwave background is 2.7 kelvin. Laboratories have cooled matter to nanokelvin, far below the temperature of deep space.
A comet's tail does not stream behind it
Comet tails point roughly away from the Sun. A comet on its way out of the inner solar system can travel tail-first.
Astronauts come home taller
Without the daily load of gravity the spine lengthens. Astronauts gain a few centimetres in space and lose them again after landing.
Glass is not a slow liquid
Window glass is an amorphous solid. Medieval panes are thicker at the bottom because they were made that way, not because the glass has flowed.
A metal melts in a warm hand
Gallium melts at 29.8 °C. A solid piece of it liquefies on a palm.
Gold is yellow because of relativity
Without special relativity, gold's electron structure would make it white, like silver. Relativistic contraction of the inner orbitals shifts the absorption that gives gold its colour.
Most ordinary matter is plasma
In stars, and in much of the gas between them, atoms are ionised. Plasma is the state of most ordinary matter in the universe.
Water can boil and freeze at the same time
At the triple point — 0.01 °C and a pressure of 611 pascals — ice, liquid water, and vapour coexist. Change the volume and the liquid boils and freezes together.
A solid can be lighter than air and still not float
Silica aerogel can be made with a solid network less dense than air. It does not float away, because its pores are full of air.
The smell of rain is a molecule
The scent of rain on dry earth is largely geosmin, made by soil bacteria and thrown into the air by the impact of drops.
Tin can crumble in a cold winter
Below about 13 °C, white tin is metastable and can transform into grey tin, a brittle form that makes an object crumble.
A diamond will burn
Diamond is carbon. Heated in oxygen to roughly 700 to 900 °C, it oxidises and is gone. It does not melt in any ordinary fire.
A drop of water can skate across a hot pan
Above a critical temperature a drop does not wet the surface. It floats on its own vapour and lasts much longer than it would on a merely hot pan.
A metal can remember a shape
Nitinol, an alloy of nickel and titanium, can be bent while cool and returns to a trained shape when warmed through a phase change.
Gold can be made, and it does not pay
Nuclear reactions transmute other elements into gold. Accelerators have done it. The yield is atoms, often radioactive, and the cost exceeds the metal.
Mercury is the only metal that is liquid in a cool room
At 20 °C and ordinary pressure, mercury is the only metallic element that is a liquid. Every other metal is a solid.
A memory can be planted
People can be led to remember, with confidence and with sensory detail, an event that never happened.
The brain spends a fifth of the budget
The human brain is about two percent of body mass and, at rest, uses about twenty percent of the body's oxygen and metabolic energy.
A split brain can disagree with itself
When the corpus callosum is cut, the two hemispheres can be shown different things and can give different answers, each missing the other's stimulus.
A missing limb can still hurt
After an amputation, most people feel the limb still present. Many feel pain in it. The sensation is generated by the nervous system, not by tissue that is gone.
For some people, letters have colours
A subset of people experience stable colours for specific letters or numbers. The pairings pass consistency tests years apart. This is synesthesia.
You can miss a change happening in front of you
If a change coincides with a brief interruption — a flicker, a blink, a cut — people often fail to see it, even when it is large.
Mammoths were still alive when the pyramids were new
Woolly mammoths survived on Wrangel Island until about 2000 BCE, centuries after the Great Pyramid was finished.
The Norse reached America five centuries before Columbus
A Norse site at L'Anse aux Meadows, Newfoundland, was occupied in 1021. It is the archaeological anchor for the Vinland sagas.
The Hundred Years' War lasted 116 years
The conflict called the Hundred Years' War ran from 1337 to 1453.
The Great Wall cannot be seen from the Moon
The Great Wall of China is not visible to the naked eye from the Moon. From low orbit it is hard to pick out at all.
Napoleon was not short
Napoleon's height was about 1.68 to 1.70 metres — short by some standards now, ordinary for a Frenchman of his time.
The metre was a slice of the planet
The first definition of the metre, in 1791, was one ten-millionth of the distance from the North Pole to the equator, along the meridian through Paris.
Zero became a number, not just a gap
A placeholder for an empty column is ancient. Treating zero as a number you can add and subtract, with rules, is later. The clearest early statement is Brahmagupta's, in 628.
Your head is older than your feet
A clock higher in a gravitational field runs faster. Over a human life the difference between head and feet is less than a microsecond.
Ten days were skipped
In the Catholic world in 1582, Thursday 4 October was followed by Friday 15 October. Ten dates were removed to realign the calendar with the Sun.
The Sun you see is already eight minutes old
Sunlight takes about eight minutes and twenty seconds to reach Earth. The disc in the sky is the Sun as it was that long ago.
Some minutes have 61 seconds
Since 1972, UTC has occasionally inserted a leap second, so that 23:59:60 is a real timestamp and noon stays near the Sun.
The week is an invention
The year, the month, and the day are anchored to astronomy. The seven-day week is not. No celestial cycle completes in seven days.
A photon's journey takes no proper time
Along a light ray the proper time is zero. There is no inertial frame in which a photon sits still and wears a clock.
A fridge-bulb is still talking from the stars
Voyager 1’s transmitter radiates about 22 watts. From interstellar space, a 70-metre dish on Earth still locks onto it.
The blade runs hotter than its own melting point
In a modern jet engine the gas hitting the turbine is hotter than the melting point of the nickel alloy the blades are made of. The metal survives because it is cooled from the inside.
A lock everyone can close, and only you can open
Public-key cryptography lets you publish the method of locking a message. Strangers can lock things to you. They cannot unlock them.
A heater can move more heat than the energy it consumes
A heat pump often delivers two to four units of heat for one unit of electricity, because it is moving heat, not making it.
The pellet outran the laser, not the power plant
On 5 December 2022 a fusion target at the National Ignition Facility released 3.15 megajoules, more than the 2.05 megajoules of laser light that hit it. The building used far more energy than the pellet returned.
A four-kilometre ruler reads a fraction of a proton
LIGO’s arms are four kilometres long. A gravitational wave changes that length by a fraction of the diameter of a proton, a shift on the order of 10⁻¹⁸ metres.
The head flies a few nanometres above the disc
Inside a hard drive, the reader does not touch the platter. It flies on a film of moving air, or helium, a few nanometres up.
A reactor is steerable because some neutrons are late
About 0.65 percent of the neutrons from uranium-235 fission are born seconds later, from the decay of fission products. That delay is what control rods can keep up with.
A telescope the size of the Earth
The Event Horizon Telescope is radio dishes on separate continents, timed as one instrument. Its aperture, for the 2019 image of a black hole, was the planet.
A mirror on the Moon still answers
Retroreflectors left by Apollo crews return laser pulses sent from Earth. The round trip takes about two and a half seconds, and the distance is measured to about a millimetre.
The rocket is mostly fuel
On a typical launch to low orbit, on the order of nine tenths of the mass on the pad is propellant. The payload is a few percent.
Fissioning one gram matches tonnes of coal
Complete fission of one gram of uranium-235 releases about as much energy as burning around three tonnes of coal.
The finest chips are drawn by light that glass cannot pass
Extreme-ultraviolet lithography patterns chips with 13.5-nanometre light. Air absorbs it. Glass absorbs it. The lenses are mirrors, and the machine is a vacuum.
Noise has a speed limit
A channel with a given bandwidth and a given noise has a highest rate at which information can be sent with arbitrarily few errors. Shannon proved it in 1948. Modern links run close to it.
The navigation signal is quieter than the noise
The GPS signal at a phone’s antenna is weaker than the thermal noise in that antenna. The receiver finds it by correlating against a code it already knows.
A message can survive losing pieces of itself
Reed–Solomon codes add extra symbols so a receiver can rebuild ones that were erased or corrupted. Voyager used them. A compact disc uses them. A scratch need not be a click.
Light in a glass fibre travels at about two thirds of c
The refractive index of the glass in a communications fibre is about 1.5, so a signal in the fibre moves at about two thirds of the speed of light in vacuum.
Nearly all intercontinental traffic is on the seabed
The large majority of data between continents travels on submarine cables, not by satellite. A modern cable is about as thick as a garden hose.
The amplifiers under the ocean are powered from shore
Repeaters on a submarine cable, sitting in the dark every fifty kilometres or so, are fed by direct current sent down a copper conductor from the landing stations. On the longest routes the voltage reaches the order of ten thousand volts.
The space telescope’s mirror is a hundred nanometres of gold
The James Webb Space Telescope’s mirror is beryllium coated with a layer of gold about 100 nanometres thick, thin enough to be almost nothing, chosen because gold reflects infrared.
Sunlight pushes, and a sail has flown on it
Light carries momentum. A sail can accelerate a spacecraft with no propellant. Japan’s IKAROS demonstrated it in interplanetary space in 2010.
A book has been written in DNA and read back
In 2012 a team encoded a book of about 53,000 words, and images, into DNA, stored it, and read it back with a few errors per million bits.
The scan never saw the slice
A CT scanner does not look at a slice of you. It measures how X-rays dim along many lines through the body, and a computer solves for the densities that would cast those shadows.
The white lamp starts out blue
A common white LED is a blue diode of gallium nitride under a phosphor that turns part of the blue into yellow. The eye reads the mix as white.
The electrons take the long way around
In a lithium-ion battery the ions cross the cell. The electrons cannot. They leave the terminal, do the work in your device, and come back the other terminal.
A laboratory clock would lose less than a second since the beginning
Optical atomic clocks have reached fractional uncertainties around 10⁻¹⁸. Kept up across the age of the universe, that fraction is less than a second.
One chip holds more switches than the Earth holds people
Published counts for the densest processors of the early 2020s run past a hundred billion transistors. About eight billion people are alive.
A cosmic ray can flip a bit
Neutrons from cosmic-ray showers, and alpha particles from the materials of the chip itself, flip bits in memory. At the scale of a fleet, this is a design constraint, not a curiosity.
The medicine can be a recipe the cell cooks
An mRNA vaccine delivers a temporary recipe, inside a droplet of fat, and the cell makes the protein. The recipe is not written into the genome.
The collider’s magnets are colder than the afterglow of the Big Bang
The Large Hadron Collider’s superconducting magnets run at 1.9 kelvin. The cosmic microwave background is 2.7 kelvin. The magnets are the colder of the two.
A shape can throw a radar echo away
A faceted or smoothly curved form can send a radar reflection somewhere other than back to the transmitter. That, more than a coat of paint, is what ‘stealth’ is.
The crystal is purified, then deliberately contaminated
Electronic-grade silicon is refined to roughly one stray atom in a billion. The behaviour of a chip comes from putting a chosen impurity back, at a dose of one atom in millions to billions.
One blade is a hundred metres long
The largest offshore wind turbines fly blades longer than 100 metres. A single blade is a hollow composite wing, and three of them sweep a circle wider than many runways are long.
To turn, a spacecraft spins a wheel the other way
A reaction wheel turns a spacecraft by spinning up in the opposite direction. Angular momentum is conserved, so the body rotates the other way. No propellant is used for the turn itself.
A fuel nozzle was grown, because a drill could not reach
The fuel nozzle of the LEAP jet engine is printed in metal, as one piece, with internal passages that a drill cannot reach because they do not open in a straight line.
A centimetre is a thirtieth of a nanosecond
Light in vacuum travels 299,792,458 metres a second, so in one nanosecond it covers about thirty centimetres. A lidar measures distance by timing that trip.
The beam steers without the antenna moving
A phased array points its beam by timing. Many small antennas, each delayed by a programmed amount, add in one direction and cancel in others. The panel stays still.
The body is imaged with radio, not with X-rays
MRI maps hydrogen nuclei in a magnetic field, using radio waves. The scan itself is not ionizing radiation. The word ‘nuclear’ was dropped from the name because it frightened people.
A spacecraft can steer by dead stars
In 2017, on the International Space Station, NASA’s SEXTANT experiment fixed its position from the X-ray pulses of millisecond pulsars, without using GPS.
The quantum computer is colder than space, and it forgets
Superconducting quantum bits run near 15 millikelvin, far colder than the cosmic microwave background. They lose their state in microseconds to milliseconds. Error correction, not the cold, is the unsolved part.
Andromeda is wider in the sky than the Moon
The disk of the Andromeda galaxy spans about three degrees, roughly six times the Moon’s width. The eye only picks out the bright centre.
Australia is wider than the Moon
The Australian mainland, east to west, spans about 4,000 kilometres. The Moon’s diameter is about 3,475. The Pacific is several times wider still.
The planets fit between us and the Moon only at the far end
Lined up by their mean diameters, the eight planets span about 393,000 kilometres. The Moon’s distance runs from about 356,000 to about 406,000. They fit when it is far. They do not fit when it is near.
A neutron star’s mountains are centimetres tall
On a neutron star, a bump a few centimetres high is already at the limit of what the crust can hold. The mountains that are likely are smaller.
The Mediterranean dried up
Around six million years ago the Mediterranean basin largely evaporated, leaving salt kilometres thick. When the Atlantic broke back in, the sea returned in a flood.
The solid core is about as hot as the Sun’s face
Iron at the boundary of the inner core is estimated near 6,200 kelvin, comparable to the surface of the Sun. The pressure keeps it solid, and the ball is growing.
A diamond carried a wet mineral up from the mantle
Ringwoodite trapped inside a diamond contained about one percent water by weight. If the mantle’s transition zone is like that sample, it holds as much water as the oceans.
The Earth hums when no earthquake is happening
The planet oscillates continuously, at periods of a few minutes, with amplitudes of nanometres, even in the absence of large quakes.
One ocean current beats every river
The Florida Current carries about thirty million cubic metres of water a second. All the rivers on Earth, together, carry about one million.
Eight percent of the genome is old virus
About eight percent of human DNA is the remains of retroviruses that inserted themselves into the germline and were inherited. Nearly all of it is broken.
The fungus steers the ant through its muscles
Ophiocordyceps makes an infected ant climb, bite, and die in a place that suits the fungus. The fungal network surrounds the muscles. It does not fill the brain.
A lungfish sleeps through the drought
When its pool vanishes, an African lungfish burrows, secretes a cocoon of mucus, and estivates. Animals have been watched in that state for many months, and the classical accounts run past a year.
A chameleon changes colour by retuning a crystal
The rapid colour shift is a change in the spacing of guanine crystals in a skin cell, which changes which wavelength they reflect. It is a lattice, not a dye being pumped.
A young albatross does not land for years
After it fledges, a wandering albatross stays at sea continuously for three to seven years before it returns to a colony.
The heart beats without orders from the brain
The impulse that starts each heartbeat is made in the muscle itself, in the sinoatrial node. Nerves can speed it or slow it. They do not originate it.
The stomach replaces its lining every few days
The surface cells of the stomach turn over in a few days. The acid and the enzymes would digest the organ if the lining were a permanent structure.
The gut has as many neurons as the spinal cord
A careful count puts about 170 million neurons in the human enteric nervous system, on the same scale as the spinal cord. The gut can coordinate digestion without instructions from the brain.
There is an ice hotter than a forge
At the pressures inside a giant planet, water forms a solid oxygen lattice with liquid-like hydrogen flowing through it. Experiments have made this superionic ice at thousands of kelvin.
Squeeze sodium hard enough and it turns clear
Near two million atmospheres, sodium ceases to be a shiny metal and becomes transparent, and an insulator. Release the pressure and the metal returns.
For a few seconds a burst can outshine its galaxy
A gamma-ray burst pointed at Earth can, briefly, outshine the galaxy that hosts it. The energy is beamed. Most of the universe never sees that particular jet.
A blue whale’s heart can fall to two beats a minute
A tagged blue whale, diving off California, had a heart rate of four to eight beats a minute at depth, and at moments two. At the surface the same heart reached the high thirties.
A bacterium can be longer than a fly
Thiomargarita magnifica, from Caribbean mangroves, has cells averaging longer than nine millimetres. They are visible without a microscope. The DNA sits in membrane-bound compartments.
The most abundant photosynthetic thing was missed until 1988
Prochlorococcus is a cyanobacterium smaller than a micrometre, and it is the most numerous photosynthetic cell in the ocean. It was described in 1988 because it slipped through the nets.
A whale was still carrying a nineteenth-century harpoon
Bowheads landed in the late twentieth century contained harpoon points of a kind last made in the nineteenth. Lens chemistry puts some of these whales past a hundred years, and a few estimates near two centuries.
A date seed from Masada sprouted
A date seed excavated at Masada, radiocarbon-dated to the first century, was germinated in 2005 and grew like an ordinary date seedling.
Water has sat in the crust for a billion years
Brine from a mine in Timmins, Ontario, has a minimum residence time of about 1.5 billion years. The dating is from xenon isotopes that match an ancient atmosphere.
The sailing stones are pushed by ice the thickness of a window
Rocks on Racetrack Playa leave long trails across flat mud. In 2013 they were watched moving, shoved by thin sheets of ice in a light wind.
The ozone overhead would make a layer three millimetres thick
If every ozone molecule above you were brought to sea-level pressure and zero celsius, it would form a layer about three millimetres thick. Spread out, that is the shield.
The solid in the funnel is a liquid, and it drips
Pitch poured into a funnel in 1927 has been dripping since the stem was cut in 1930. A drop takes the better part of a decade. The experiment is still running.
A gecko sticks without glue
A gecko’s toe is covered in hundreds of thousands of hairs, split at the tips into still smaller pads. The force holding it to the wall is intermolecular attraction, and the toe lets go by changing its angle.
Saturn’s north pole is a hexagon
A jet stream around Saturn’s north pole has six straight sides. It is about 30,000 kilometres across, and it has kept the shape since Voyager photographed it in 1980.
A sunset on Mars is blue
The Martian daytime sky is butterscotch. Around the setting sun it turns blue. Fine dust scatters the red light out of the beam and lets the blue continue forward.
A volcano on Mars is the size of a state
Olympus Mons is about 600 kilometres across and about 22 kilometres high, roughly two and a half times the height of Everest. The slope is so gentle that from the base the summit is over the horizon.
Uranus rolls around the Sun on its side
Uranus is tilted by about 98 degrees. Its poles take turns pointing at the Sun, and a season there lasts about twenty-one years.
A cicada spends seventeen years underground, then comes up with all the others
Periodical cicadas live as nymphs below ground for 13 or 17 years, feeding on the sap of roots. Then a whole brood emerges within days, mates, and is gone in weeks.
The brain itself cannot feel the surgeon
The cerebral cortex has no pain receptors. Surgery on it can be done with the patient awake, speaking, while the scalp and the lining around the brain are the parts that hurt.
A dreamer can signal, with eye movements, that the dream is lucid
People trained to notice they are dreaming can, during confirmed REM sleep, make a prearranged pattern of eye movements. The pattern shows up on the recorder. The dream continues.
In some anglerfishes, the male fuses to the female
In certain deep-sea anglerfishes a tiny male bites a female and the tissues join. His blood supply becomes hers. He lives on as a source of sperm, fed by her bloodstream.
Europa holds an ocean under the ice
Jupiter’s moon Europa has a shell of ice over a global ocean of liquid water. Magnetic measurements from Galileo are the evidence. The ocean may hold more water than all of Earth’s seas.
In a reactor pool, particles outrun light
Light in water travels at about three quarters of its speed in vacuum. A charged particle from a reactor can go faster than that. The result is a blue glow.
A nuclear reactor ran in Gabon with no one to build it
About 1.7 billion years ago, uranium ore at Oklo went critical. Groundwater was the moderator. The fission products are still in the rock.
Light has been slowed to the speed of a bicycle
In a cold cloud of sodium atoms, a light pulse crawled at 17 metres a second. That is about sixty kilometres an hour. In vacuum it still does 300,000 kilometres a second.
Bacteria keep a file of the viruses that attacked them
A CRISPR array is a list, written in DNA, of snippets taken from viruses. The cell uses the list to recognise those viruses and cut them. The gene-editing tool is that immune system, borrowed.
A turtle’s shell is its ribs
The carapace is not a house the animal sits in. It is the backbone and the ribs, grown outward and fused into bone the shoulder blades end up inside.
A fish in the Antarctic has no haemoglobin
Icefish have no red blood cells and no haemoglobin. The blood is clear. Oxygen rides in the plasma, and the cold sea holds enough of it for that to work.
A sea slug keeps the chloroplasts of the algae it eats
Elysia takes chloroplasts from its food and holds them inside its own cells, where they go on absorbing light for weeks to months. The slug does not make them, and it does not become a plant.
A Venus flytrap counts to decide whether the meal is real
Two touches on the trigger hairs, within about twenty seconds, shut the trap. Further touches — about five — start the digestive glands. The tally is a series of electrical impulses.
A thousand amoebae can become one crawling thing
When Dictyostelium runs out of bacteria, the separate cells signal, stream together, and assemble into a slug that migrates as a single body. Then some of them die to build a stalk.
A dolphin sleeps with one half of the brain
In slow-wave sleep, dolphins put one hemisphere to sleep at a time. The other stays awake, one eye stays open, and the animal surfaces to breathe.
An Arctic tern flies nearly twice around the Earth in a year
Geolocators on Arctic terns recorded annual trips of about seventy thousand kilometres, and more than eighty thousand for some birds. The circumference of the Earth is forty thousand.
A wild bird recruits people to open a bees’ nest
The greater honeyguide leads honey-hunters to a hive it cannot open, with a call and a flight from tree to tree. The people smoke the bees and break in. The bird eats the wax.
A bird’s breath does not come back the way it went
Air flows through a bird’s lung in one direction, from back to front, both when the bird inhales and when it exhales. The air sacs, not the lungs, are the bellows.
Dragonflies arrive across open ocean, where no larva could have lived
Globe skimmers turn up on islands and ships hundreds of kilometres from the nearest fresh water. Their young can develop only in fresh water. The adults crossed.
A wave twice as high as the sea around it was measured
On 1 January 1995 a laser on the Draupner platform recorded a wave 25.6 metres high, in a sea whose significant wave height was about 12 metres. It was the first rogue wave caught by an instrument.
In deep water a tsunami is a low swell moving at jet speed
A tsunami in the open ocean is often under a metre high and hundreds of kilometres long, travelling at about 700 to 800 kilometres an hour. It stands up only when the sea becomes shallow.
A salamander grows the limb back, bones and all
An axolotl that loses a leg regrows the leg: skeleton, muscle, nerves, and skin, in the right pattern, without a scar. The cells at the stump remember what tissue they were.
A bacterium can have its genome shattered and stitch it back
Deinococcus radiodurans survives acute radiation of thousands of grays, which shatters its chromosomes into hundreds of pieces. It then reassembles them. A few grays kills a person.
An octopus edits its RNA, especially in the nervous system
Cephalopods recode RNA transcripts at tens of thousands of sites, heavily in the nervous system, far beyond what a vertebrate does. The genome says one thing. The message that is read often says another.
A reindeer’s eyes change colour in winter
The mirror behind a reindeer’s retina is gold in summer and deep blue in winter. The shift tracks the months of darkness, and it changes which light is reflected back through the retina.
A Portuguese man-of-war is not one animal
Physalia is a siphonophore: a colony of specialised individuals — the float, the stinging tentacles, the feeding parts, the reproductive parts — budded from one larva and unable to live apart.
The compass has pointed south
Earth's magnetic field has reversed, many times. The ocean floor is striped with the record: rock that froze while the compass pointed the other way.
The iron in blood was made in a star
The Big Bang made hydrogen, helium, and a trace of lithium. Iron was forged later, in massive stars, and scattered when those stars died. The iron in haemoglobin is that debris.
Gold is forged when dead stars collide
The collision of two neutron stars, watched in 2017, produced a cloud of the heavy elements. Gold is in that family. How much of Earth's gold came that way is still a share, not a census.
An aphid can be born already pregnant
In the summer generations, a female aphid gives live birth to daughters who already contain embryos. A grandmother, a mother, and a granddaughter are nested in one body.
A goose flies over the Himalayas under its own power
Bar-headed geese climb from near sea level to between 4,000 and 6,000 metres in a single day, flapping, often at night, without needing an updraft to do it.
A sponge pushed through a cloth can assemble itself again
Separate the cells of a sponge and, left in seawater, they crawl back together and rebuild a sponge, with the cell types sorted into the right layers.
Bread wheat is three grasses that never came apart
The wheat in a loaf carries three complete ancestral genomes. Two wild hybridisations stacked them, and the plant kept all three instead of choosing.
Maize cannot scatter its own seed
The wild ancestor of maize shatters its seed head and sows itself. The cob does not. The kernels wait to be picked. Without people, the plant does not travel.
The export banana is one clone, and the last one died of a fungus
The banana of international trade, Cavendish, is propagated by cuttings, so each plant is genetically the same plant. The clone it replaced, Gros Michel, was wrecked commercially by Panama disease.
The remote Pacific was settled without a compass
Navigators in oceangoing canoes reached islands scattered across millions of square kilometres, steering by stars, swell, birds and clouds. The magnetic compass was not part of the kit.
The Moon rang for about an hour after a strike
Apollo seismometers recorded the shock of impacts reverberating in the lunar crust for tens of minutes, sometimes about an hour. The Moon is dry, and dry rock does not damp a wave the way Earth does.
The air above you weighs about a kilogram on every square centimetre
Sea-level pressure is about 101,000 pascals. That is the weight of a kilogram pressing on each square centimetre of you, from every direction at once.
A dung beetle steers by the Milky Way
On moonless nights, a dung beetle rolls its ball in a straight line by keeping a heading against the band of the Milky Way. Hide the sky and the path curls.
A bird navigates a cave by clicking
The oilbird nests in caves and finds its way in the dark by echolocation. The clicks are slow enough to hear. The system is coarser than a bat's, and it works.
An Antarctic fish stays liquid in water colder than its freezing point
The sea under the ice is about minus 1.9 degrees. The blood of a notothenioid fish would freeze at a higher temperature than that, except for proteins that bind tiny ice crystals and stop them growing.
A locust is a grasshopper that changes its body when the crowd arrives
The desert locust has two forms. Alone, it is a cryptic grasshopper. Crowded, it changes colour, shape, brain and behaviour, and it swarms. Same genes. Different life.
A bee can find the Sun through cloud, by the polarisation of the sky
Sunlight scattered by air is polarised in a pattern that points back to the Sun. A bee can see that pattern, and can steer by it when the Sun itself is behind cloud, so long as some blue sky remains.
An elephant keeps spare copies of the gene that stops a tumour
Elephants carry about twenty copies of TP53, the gene whose protein makes a damaged cell stop or die. Humans have one working copy. Elephants still get cancer. They get less of it than their size predicts.
A salmon finds its river by the smell
Young salmon imprint on the chemistry of their home stream. Years later, coming back from the ocean, they choose that stream by its odour. Block the nose and the choice fails.
Thunderclouds fire beams of antimatter upward
A terrestrial gamma-ray flash in a storm makes pairs of electrons and positrons. NASA's Fermi telescope has caught the positrons travelling out along Earth's magnetic field, including from storms over the horizon.
The Amazon is fertilised by dust from the Sahara
Satellite measurements trace a plume of African dust across the Atlantic and onto the Amazon, carrying on the order of twenty thousand tonnes of phosphorus a year. The forest's soil is poor. The desert makes up some of the difference.
A virus was filed as a bacterium because it was big enough to see
Mimivirus is about 0.4 micrometres across, visible in a light microscope, with a genome larger than some bacteria. It was stained, named as a microbe, and only later recognised as a virus that infects amoebae.
A virus can be infected by a smaller virus
Sputnik replicates inside the factory that a giant virus builds in an amoeba. Where Sputnik is present, the giant virus produces fewer and deformed particles. The small one is a parasite of the large one.
A bacterium in an insect can turn males into females
Wolbachia is passed only through eggs. Males are a dead end for it. In different hosts it kills male embryos, lets females reproduce without mating, or converts genetic males into females.
A fungus replaces a cicada's abdomen, and the cicada keeps flying
Massospora consumes the rear of an adult cicada and turns it into a mass of spores. The insect, abdomen gone, continues to fly and to seek mates, and in doing so spreads the fungus.
A caterpillar, eaten hollow, stays to guard the wasp's young
After parasitic wasp larvae chew out of a caterpillar and pupate beside it, the dying caterpillar thrashes at anything that approaches them. Caterpillars that do this lose fewer of the pupae to predators.
A plant with no leaves finds its victim by smell
Dodder seedlings grow toward the volatile chemicals of a host plant. They prefer a tomato to a wheat stalk, and they do it before they have touched either.
A lichen is not two organisms. In many, it is three
For a century a lichen was a fungus farming an alga. In 2016 a second fungus, a yeast, was found living in the cortex of many common lichens, and its abundance tracks how the lichen looks.
The nerve to your voice box loops down through the chest
The recurrent laryngeal nerve leaves the skull, descends into the chest, passes under a vessel by the heart, and climbs back to the larynx. In a giraffe the same detour is a path of metres, to reach a target a few centimetres from where the detour began.
Two bones of your middle ear used to be part of the jaw
The malleus and the incus, which pass sound across the middle ear, are the articular and the quadrate, the jaw joint of a reptile. Mammals bite with a different pair of bones. The old pair was free to hear.
An electric eel leaps out of the water to deliver the shock
When a threat is partly out of the water, an electric eel rises, presses its chin against it, and uses the lifted body as the live path of the circuit. The current no longer leaks away through the river.
A mole locates food by the difference between its two nostrils
The common mole's nostrils sample slightly different air. Block one, or cross the scent with tubes, and the animal can no longer turn toward the smell. It was using the difference.
A pit viper sees warm bodies with an organ that is not an eye
The pit between eye and nostril is a pinhole camera for infrared. It forms a crude image of heat, on a membrane, and the brain overlays that image on vision. The molecular sensor is a channel that in you helps feel pain.
A cuttlefish's skin responds to light without the eyes
Chromatophores in cuttlefish skin expand when the skin itself is lit. The response does not require the eyes, or a signal from the brain. The skin has light-sensitive pigments of its own.
A glass sponge coordinates its whole body, and it has no nervous system
Hexactinellid sponges are a syncytium, one continuous cytoplasm. A single electrical impulse crosses the body and stops every feeding chamber at once. There are no neurons to carry it.
Io is melted by the flexing of its orbit, not by the Sun
Jupiter's innermost large moon is the most volcanic body in the solar system. The heat is tidal. The orbit is kept slightly squashed by the other moons, so Io is kneaded, continuously, as it goes around.
A frog swallowed her eggs and gave birth through her mouth
The gastric-brooding frog shut down her stomach acid, swallowed the fertilised eggs, raised the young in her stomach, and opened her mouth to let froglets out. Both species are extinct.
A horseshoe crab's blood is how drugs are checked for bacterial debris
Cells in Limulus blood clot when they meet endotoxin, a fragment of bacterial wall. That clot became the standard test for whether an injectable drug or a device was contaminated. A recombinant copy is now replacing the crabs.
A grove of aspens can be one tree
Quaking aspen spreads by roots that send up new trunks. A stand of thousands of stems, covering hectares, can be a single genetic individual. The famous one in Utah is a forest you can walk through, and it is one plant.