A 2003 genetic study linked a shared Y-chromosome lineage found across much of Asia to a common ancestor who may have lived around 1000 CE, a period that connects to Genghis Khan's family. The link is circumstantial, and geneticists note important limits on what it shows.
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Brain freeze is a brief headache set off by very cold food or drink on the palate. Its exact mechanism is still debated, involving the trigeminal nerve and blood flow.
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Human blood is always some shade of red, bright with oxygen and darker without it. Veins look blue because of how light interacts with skin and vessel walls.
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In 1854 Snow mapped cholera deaths in Soho, found them clustered around the Broad Street pump, and used interviews and records to explain apparent exceptions.
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Vaccines show the immune system a harmless version or piece of a germ, or instructions to make one, so it makes antibodies and memory cells ready for a real infection.
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The gut microbiome is the community of microbes in your intestines. It aids digestion and immunity, but proof that it causes disease is strong only for a few conditions.
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Sleep is essential, but its core purpose is still unresolved. Several theories, likely overlapping, point to energy saving, bodily and brain restoration, and brain plasticity.
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Researchers have no settled answer. Leading ideas link yawning to brain arousal and cooling, and contagious yawning to empathy, group synchrony and vigilance.
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Waking a sleepwalker does not itself cause medical harm, though confusion or fear can follow. Most sources advise guiding them back to bed, and waking them gently if they are in danger.
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Cats purr in many situations, from contentment and greeting to stress and pain. Scientists still do not fully agree on why, or exactly how, the sound is made.
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Birds combine a compass (sun, stars, magnetic field) with landmarks and smell, and cross-check these cues rather than relying on any single one.
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A forager's figure-eight dance encodes distance in the length of its waggle run and direction in the run's angle from vertical, which stands for the angle from the sun.
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Ageing is mostly explained as a by-product of evolution, since selection weakens after reproduction. Biologists still debate whether it is a side effect or an optimised trade-off.
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Evolutionary mismatch is the idea that a trait shaped by one environment can become harmful when the environment changes faster than evolution can respond.
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The Prisoner's Dilemma shows that one-shot interactions favor defection. Cooperation can evolve when interactions repeat, as with reciprocity strategies like tit-for-tat.
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Watson and Crick built the double helix model in 1953 by combining model building, Chargaff's base ratios and Rosalind Franklin's X-ray diffraction data, including Photograph 51.
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CRISPR uses a guide RNA to lead a Cas enzyme, usually Cas9, to a matching DNA sequence. The enzyme cuts the DNA, and the cell's own repair process then changes the sequence.
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Octopuses use ADAR enzymes to convert adenosine to inosine in their RNA, which ribosomes read as guanine. This changes many proteins without altering the DNA.
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The claim that people swallow several spiders a year in their sleep is a myth. Swallowing one is not strictly impossible, but it would be a rare, random event with no documented case.
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No. Studies comparing habitual knuckle crackers with non-crackers have found no increased arthritis, though forceful cracking can occasionally cause injury.
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No. The head loses heat roughly in proportion to its share of body surface, about 7 to 10 percent. The myth persists because heads are often the only uncovered part in the cold.
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No. Bulls are red-green colorblind and charge at movement and perceived threat, not at red. Why the bullfighter's cape is red is less certain.
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No. The three-second claim is a myth. Research shows goldfish remember for weeks, months and possibly longer, and they can learn routines, cues and tasks.
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No. All bats can see. Their vision varies by species, and many also use echolocation, often together with sight rather than instead of it.
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