How the heart achieves its first beat

Dozens of US research projects focus on the zebrafish's ability to grow new retina cells

The small, striped minnow can repair its optic nerve in just under a week. Scientists are interested in hacking its regenerative capacity to grow new retina cells to treat human eye disorders, including macular degeneration. In 2020, the US National Eye Institute had nearly 80 projects focused on zebrafish.

What does a beating human heart look like?

Tucked behind your rib cage and between your lungs sits your heart. This knot of cardiac muscle will (typically) beat billions of times throughout your lifetime, sending oxygenated and nutrient-rich blood throughout the body, powering countless biological processes that have enabled you to read this very paragraph. This two-minute video provides a glimpse of the mechanics happening inside your chest via an animated anatomical model.

Watch a salamander grow from fertilization to hatching

New microscopy techniques have allowed scientists to image the development of animal embryos with unprecedented detail. This six-minute time-lapse reveals the development of a salamander from initial fertilization to hatching from an egg.

In 1984, a dying infant lived for three weeks with a baboon heart

Pediatric-sized hearts are very hard to find. They're about the size of a walnut. When a premature baby girl was born with a fatal heart defect in 1984 her care team transplanted a 7-month-old baboon's heart into the patient. The organ was not genetically modified but still the infant lived for several weeks. This roughly hour-long documentary from the medical institution, features the patient's mother, clinician, and more discussing the controversial procedure and aftermath.

The hormone that spreads love and helps fish share fear

Scientists consider emotions like fear and empathy to be among the oldest evolutionary behaviors observed in mammals. Yet to date, how these reactions are processed in the brain, regardless of species, is not well understood. A new study reveals how the chemical oxytocin—known as the "love hormone" in humans—helps let fish know when their friends are in danger.

What happens during the first eight weeks of pregnancy?

The first weeks of embryonic development, known as embryogenesis, are one of the most critical phases during pregnancy. This simple breakdown from the Khan Academy illustrates what we know about how the complex process unfolds.

The earliest known cardiovascular system dates to 520 million years ago

The earliest evidence of a cardiovascular system and blood-like substance may date back to the Cambrian period in an ancient arthropod. This 2014 academic article includes images of the ancient cardiovascular system, which remains one of the most detailed samples of Cambrian arthropod anatomy.

'Artificial embryos': The hidden steps in forming a spine

Somitogenesis is the process by which segmented body structures like vertebrae form in embryos. While the process is well understood in animals like mice or zebrafish it is difficult to study in humans. But now, researchers have created a model of somitogenesis, using pluripotent stem cells, called an axioloid.

Scientists first observed a sperm and an egg uniting in 1876

Throughout human history, scholars and researchers have speculated on the origin of human reproduction. It wasn't until the late-19th century that the physical process of egg fertilization via sperm cells was observed (in sea urchins), forming the basis for modern fertility research.

Pig brain cellular activity was restarted hours after death in study published in 2019

Yale University scientists restored basic cellular activity and circulatory function in pig brains about four hours after death with a synthetic cocktail of preservatives and nutrients. This work— which didn't restart electricity activity in the brain or consciousness—could help advance future human stroke and brain injury treatments.

Fruit fly experiments helped identify genes responsible for major body development

The insects' fast life cycle and affordability have allowed geneticists to quickly identify which genes are responsible for limbs, eyes, and other body structures by inducing mutations. The same genes may be responsible for different parts of a species' body, such as limb-building genes being responsible for wing pigmentation in butterflies.

Zika virus shocked scientists because the mosquito-borne disease causes birth defects

This revelation, confirmed in 2016, marked the first time that a mosquito-borne disease was known to cause birth defects. Fetuses exposed to the Zika virus during pregnancy sometimes suffer from neurological complications and microcephaly, a small-headed condition associated with neurological development issues and impairment.

The Lazarus Effect is when a heart begins beating on its own after declared death

Formally called autoresuscitation, this rare phenomenon occurs when someone is declared dead following a cardiac arrest but their heart beats again without help—making it seem like the person came back to life. Doctors don't know the exact cause.

A dispute about the origin of twitching frog legs led to the invention of the first battery

Experiments by Luigi Galvani on exposed frog leg nerves showed activity when they were hung from iron railings and brass hooks, suggesting the existence of "animal electricity" that discharged when connected to metals. Alessandro Volta's voltaic pile, which stacked metals with an inorganic electrolyte, showed that electricity originates from chemical reactions.

Rune Elmqvist forwent practicing medicine to invent the first inkjet printer

The Mingograph recorded real-time physiological signals from a patient's electrocardiogram, helping doctors diagnose heart and brain conditions. Eight years later, in 1958, Elmqvist worked with cardiac surgeon Åke Senning to develop the first fully implantable pacemaker.

Why do dreamers twitch?

This thought-provoking piece highlights newer research suggesting sleep twitches may not be random dream leftovers, but instead a crucial way our brains map and understand our bodies. From sleeping rat pups to dreaming octopi, this biological mapping system appears universal across animal species.

A look at how fish less than two inches long climb up 50-foot waterfalls

Shellears use tiny hooks on their front pectoral fins to grip rock like Velcro and take many pauses to recover energy between bursts of movement. Their pectoral girdle—an arch of bone—supports the muscle system needed for the roughly ten-hour climb.

Mechanical watches measure the passage of time via the vibration of a quartz crystal

When electricity from a battery passes through the crystal inside a watch, the crystal vibrates, creating an electrical signal with a precise frequency of one vibration per second. This signal moves the hand of the watch so that it ticks once per second, allowing it to track the passage of time.

Coral polyps reproduce via broadcast spawning, where entire reefs simultaneously release reproductive cells for about one hour, once a year.

Listen to the earliest known recording of a whale song

A recording of a humpback whale was taken by scientists from the Woods Hole Oceanographic Institution near Bermuda in 1949, but forgotten for decades. When first captured, researchers didn't know what animal they were hearing, and therefore didn't catalogue the recording. The well-preserved audio was found by the team's archivist in 2025.

Learn how your body is, scientifically, like a firework with its own slow, controlled burn.

South American lungfish has the largest animal genome, with 91 billion base pairs

This genome is 30 times larger than a human's due to significant amounts of "junk DNA" and jumping genes, or transposons. Transposons can jump or copy over to other parts of a genome and may aid adaptation.

New blood cells are created by hematopoietic stem cells

Blood is made up of several cells with various functions and short lifespans, so the body must have a constant supply of replacements. These replacements are created by hematopoietic stem cells, rare cells that live in bone marrow and can regenerate themselves and blood cells.

The first nuclear reactor was built three years after nuclear fission was discovered

After learning that large atomic nuclei release energy upon being split apart, scientists quickly researched how to control the reaction to make electricity. Fusion—combining small atomic nuclei—generates massive energy in stars and hydrogen bombs.

How does your body turn food into energy?

Cells get energy via a process known as cellular respiration, which involves turning glucose into ATP or adenosine triphosphate. Breaking the phosphate bonds of ATP results in usable energy being released into cells, which can then use that energy to power biological processes. This 10-minute video explains how glucose turns into ATP, giving the body the energy it needs to survive.

When caught in the mouths of cardinal fish, seed shrimp release glowing, bioluminescent chemicals, which alert predators of the cardinal fish, prompting the shrimp's ejection.

Single-cell organisms have circadian clocks that direct daily biochemical routines

Cyanobacteria, a type of light-sensitive bacteria, use this clock to signal when to alternate between making organic compounds through photosynthesis and when to convert atmospheric nitrogen into usable ammonia. Upregulating photosynthetic machinery before dawn helps ensure efficient photosynthesis.

Fish populations in the Great Barrier Reef have increased after installing waterproof speakers on the ocean floor that played recordings of sounds from healthy coral reefs.

Bone marrow (soft tissue found inside certain bones) generates roughly 500 billion new blood cells each day

Planarian flatworms are small, aquatic worms with exceptional regenerative capabilities. When cut, the worms can regenerate multiple bodies in a matter of weeks.

After 25 people used virtual reality headsets to practice flying with virtual wings—flapping their arms—their visual cortex responded to the wings almost as if they were real arms, treating them as body parts.

See how each of the more than two million known species relates to each other—and to common ancestors—in this zoomable tree of life.

Studies suggest when you sleep is as important as how much you get, and syncing with your circadian rhythms may lead to less fatigue and improved long-term health outcomes

The syncytiotrophoblast is the outer layer of the placenta and the largest human cell, spanning an area about twice that of a king-sized bedsheet.

The animatronic shark from Steven Spielberg's 'Jaws,' the first modern blockbuster, was a complex underwater apparatus called 'Bruce.'

English mathematician Ada Lovelace wrote the first computer algorithm a century before computers existed and hypothesized that computing devices would one day be able to compose music—foreseeing the generative AI systems of today.

Ebola infects and disables immune cells, triggering a cascade of events that leads to small blood clots throughout the body, weakening blood vessels and interrupting blood flow to key organs.

Visualize how CRISPR-Cas9—a type of immune system used by single-celled organisms to attack invasive viruses—targets and makes precise changes to a gene's DNA.

Indefinite cloning of some endangered species may not sustain their longevity because cloning success rates decrease as genetic mutations accumulate.

How Amazon operates a 'flywheel' business model, a self-reinforcing cycle that drives continuous growth

Hear 50 years of iconic hip-hop samples, the genre's foundational looped tracks

The idea for the Federal Reserve was conceived in secret in 1910—with bankers donning duck hunt gear for disguise while traveling to a remote country club on Georgia's Jekyll Island

Long before Major League Baseball began allowing instant replay for balls and strikes, an umpire reluctantly used the technology to determine whether a hit was a home run, a move that inadvertently ushered in a new era for the sport.

Pure water does not conduct electricity because this flow of energy requires the movement of charged particles, and water is a neutral molecule.

Explore chaos in this simulation of two double pendulums, where small differences in the release angles produce wildly different outcomes.

The first image of a black hole was captured by creating an Earth-sized virtual observatory from a network of eight radio telescopes.

The word 'jazz' evolved from 'jasm,' 19th-century American slang for 'energy'

The first steps to rebuilding your credit score include getting to know exactly what's on your credit report and figuring out how far you are from the '700 club,' or 'good score' range.

Venture capital is a form of funding provided to early-stage companies with high growth potential, typically in exchange for an equity (or ownership) stake

The Beatles' US label rejected the band's first two singles, 'Please Please Me' and 'From Me to You,' with one executive calling the band 'dead in the water.'