Blood evolved many times over hundreds of millions of years

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.

The history of blood, as told by a hematologist

Since ancient times, blood has been seen as a semi-magical substance. Alchemists theorized it was a mixture of the four elements. Others proposed it was one of four bodily fluids whose balance dictated health. This 2019 essay by a hematologist reviews blood's reputation across cultures and centuries.

When was the first blood transfusion?

In the 1600s, an English doctor transferred the blood from one dog to another via quills. The procedure ended when one of the dogs died. This article details the early days of blood transfusions, which turned toward humans shortly after the 1666 dog experiment and involved putting the blood of a sheep into a human recipient (who reportedly survived the encounter).

The economics of horseshoe crab blood

Horseshoe crabs are older than dinosaurs and have survived five mass extinctions that wiped most life from the planet. But it's only now that their future as a species is in danger. This blood, worth about $60,000 per gallon, is hyper-sensitized to certain bacteria that are fatal to humans. This 17-minute podcast dives into humanity's pursuit of horseshoe crab blood, a "somewhat magical" mixture heavily relied on by the pharmaceutical industry.

Evidence of cancer has been found in a 1.7-million-year-old fossil

Cancer has existed as long as humans have, with some of the earliest evidence found among fossilized bone tumors, human mummies in ancient Egypt, and ancient manuscripts. The oldest example was uncovered in a toe—millions of years old—from an ancestor of modern-day humans.

Vampire bats are the only mammal to feed exclusively on blood

Scientists believe their ancestors may have eaten parasites and insects off larger animals until vampire bats started feeding directly from those animals. Colonies work together to stay fed, as a vampire bat can die without just two days of eating.

Genetic analysis suggests Anopheles mosquitoes fed on humans some 1.8 million years ago

The 2026 paper, based on 11 species of Anopheles mosquitoes found in Southeast Asia, suggests that mosquitoes in the region likely developed their human blood preference between 2.9 million and 1.6 million years ago, overlapping with when scientists believe Homo erectus arrived there. (Some users may encounter a paywall.)

Why don't we synthesize blood?

We're trying. Scientists are currently working on creating viable synthetic blood, an alternative to the presently relied-upon donations that manage to fall short of demand. More than half of the world's nations struggle to meet their population's need for blood. This article details current and historical efforts to develop synthetic blood, a venture that started more than 400 years ago.

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 word 'vampire' appeared in the English-speaking world in the 1730s

However, earlier mentions of creatures with similar characteristics existed throughout Medieval Europe. For example, people often spoke of revenants—restless dead creatures who tormented the living. Historians believe these stories grew in popularity in part because of influence from the Catholic Church, which was emphasizing the idea of purgatory. These older revenant stories eventually influenced modern vampire folklore.

Human anatomy provides evidence for evolution

Throughout history, scientists have used anatomy to support the Theory of Evolution in three main ways. Homologous structures, or similar physical features in organisms that serve different functions, can help scientists understand common ancestors....

Evidence suggests the first cells on Earth were bacteria

About 4 billion years ago, these single-celled organisms harvested carbon dioxide and sunlight to produce their own food and oxygen, setting the stage for the evolution of oxygen-breathing life forms. Archaeabacteria, which thrive on inorganic molecules in extreme habitats on Earth today, were also among the earliest organisms.

Snake venoms are repurposed proteins responsible for other bodily functions

Just as saliva aids digestion in humans, proteins responsible for bioactivities such as digestion and blood clotting were eventually secreted in the glands and fangs of snakes across evolutionary history. Organisms that could not withstand the effects of these molecules (e.g., excessive bloodstream clotting) became ideal prey for snakes.

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

Here's how early humans lived

Explore the evidence of early human behavior—from ancient footprints to stone tools and the earliest symbols and art – along with similarities and differences in the behavior of other primate species.

The tongue evolved in animals roughly 350 million years ago

Creatures like fish rely on suction to consume food, flexing their gills to create water currents that vacuum up their meals. The evolution of the tongue enabled vertebrates to completely cut ties with the sea, moving onto land where they could sample new foods and ways to eat them.

Three examples of how humans are still evolving

For much of nature, natural selection and "survival of the fittest" still play a dominant role; only the strongest can survive in the wild. As little as a few hundred years ago, the same was true for humans, but what about now?

The origin of cyborgs

The term "cyborg" was coined in a 1960 academic paper discussing what alterations humans would need to undergo to survive in extraterrestrial environments, a venture far "more logical than providing an earthly environment" in space. According to authors Manfred E. Clynes and Nathan S. Kline, Cyborgs with a capital C have incorporated exogenous components that extend their ability to adapt to new environments. Read the paper here.

New evidence suggests the eruption's victims died as their blood boiled

While most Pompeii victims suffocated or were crushed, spectroscopic analysis of bones from a nearby town indicates something more extreme: exposure to superheated gas that instantly boiled blood and caused deadly internal trauma.

Red blood, skin, hair, and nail cells destroy their DNA upon maturing

To maximize the amount of oxygen they carry and more easily alter their shape to fit into narrow blood capillaries, red blood cells destroy their own nuclei. Cornified cells found in hair, nails, and the outermost layer of skin destroy their nuclei and other cellular contents to make room for keratin, which provides durability and structural support.

The ultrarare 'Er' blood type has been documented only about 40 times

In 2022, the tragic loss of a pregnancy led researchers to the discovery that the rare "Er" blood type could potentially cause a mismatch in blood types between mother and fetus during pregnancy, with devastating consequences. (Some users may encounter a paywall.)

The ancestors of ostriches and emus could fly

The discovery of a 56 million-year-old fossil bone helps explain how this (mostly) flightless family of birds spread to so many different continents.

What did it take to eat like a gladiator?

If you think gladiators were all rippling muscle, think again. Evidence suggests fighters weren't as cut as we've been led to believe. This article dives into the diets of ancient Roman gladiators, who may have eaten mostly vegetarian. Archaeological evidence gathered from the skeletons of 68 gladiators found in a 2,000-year-old Turkish grave suggests the fighters' diets mainly relied on barley and legumes, with little animal protein.

Horror evolved from Gothic literature

Although creepy tales can be found in nearly every folk tradition, the roots of modern horror can be traced back to Gothic literature, which focused on the battle between humans and unnatural, evil forces.

A four-billion-year-old meteorite reignited the debate about life on Mars

Recovered from Antarctica in 1984, ALH84001 contained organic compounds, magnetite and iron sulfide grains of potential biological origin, and features that resembled fossilized bacteria. With technological advancements, scientists found abiotic origins for these features in the following decades.

More than 100 types of beer are produced around the world

Beer dates back to ancient times, and since then, the fermented drink has taken on many different styles around the globe, depending on the grain and ingredients used. See how pilsners, IPAs, Sours, and other types evolved from the drink's early history.

The first line of 'immortal' human cells, which can divide indefinitely and are used in scientific research, was nonconsensually taken from a Black woman.

Scientists have struggled to pin down Ebola's natural reservoir species for decades, but the available evidence suggests that it's very likely fruit and insect-eating bats found in Africa.

The Dracula character, now seen as the vampire archetype, was inspired by a seafood-induced nightmare its creator experienced.

See these 16 pieces of art evoking phobias of snakes, flying, spiders, and more. 

Tattoos remain visible on your skin thanks to immune cells called macrophages

Larger animals like giraffes, elephants, and blue whales have developed a unique defense against cancer, a phenomenon known as Peto's Paradox

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.

The American cockroach is actually from Africa, an apparent hitchhiker aboard ships carrying enslaved people, with evidence suggesting the bug may have arrived in the New World as early as the 1600s.

The concept of phantom limbs, the perception that amputated limbs are still present, dates back to a French military surgeon in the 16th century.

Read a deep dive on the 'all-purpose healing' peptide BPC-157.

Volcanic activity may have triggered the Black Death by spewing gases that led to crop failures in Europe, thus forcing the import of grain ships with plague-infested fleas.

Before humans, the Soviet Union and the United States sent animals—including apes, dogs, and cats—to space during the Space Race.

Crows are believed to have intelligence on par with a seven-year-old child and demonstrate complex behaviors, from problem-solving with tools to recognizing human faces.

While atoms are normally made of protons, neutrons, and electrons, exotic ones have been built with antimatter—alternate versions of normal matter that live for fractions of a second and are about a billion times as rare.

The Great Salt Lake's distinct dual coloration results from high-salinity organisms that only live in the northern portion and produce a purple protein.

Budweiser stores yeast derived from the original 1800s strain in a secret bunker, which only the Head of Yeast Management can access—not even the CEO

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

Urushiol, the oily toxin in poison ivy, can remain allergenic on clothing for years.

Graffiti dates back to at least ancient Pompeii, where citizens scrawled messages to one another on public walls

For centuries, it was common to sleep in two shifts: a few hours at the beginning of the night, and a longer period beginning around midnight

Scientists can determine Earth's past climate conditions by analyzing air trapped in microscopic bubbles within ice cores—columns of compressed snow layers that build up over hundreds of thousands of years.

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

While the first exchange-traded fund (a 'basket' of different assets that can be bought and sold on a stock exchange) in the US only launched in 1993, the global ETF market has grown to more than $10T in the short time since.

The Brothers Grimm were lawyers before they were storytellers, but became interested in fairy tales as they began investigating how rules and customs had been passed down through cultures.