A brief history of human blood groups

The proteins and sugars on the surface of your blood cells determine your blood type

The antigens dotting the outside of a red blood cell determine blood type. That's why the four main blood types are A, B, AB, and O, each with positive and negative variations. Secondly, the presence or absence of the Rh factor protein determines whether the type is positive or negative.

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.

An interactive explanation of blood transfusion

The antigens and Rh factors of blood cells (which determines your blood type) must be compatible with your immune system—which is why blood transfusions between patients must have matching types. In a mismatch, the immune system will attack and destroy donor blood cells, triggering a potentially fatal reaction.

Blood evolved many times over hundreds of millions of years

The earliest evidence of a blood-like substance comes from ancient arthropods, which appear to have had copper-based blood. In the 500 million years since then, some creatures have grown to rely on other variants, such as humanity's iron-based blood.

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).

How did segregation in the US affect blood donations?

When the US established its first nationwide network of blood banks in 1941 with the hopes of restoring the dwindling reserves of military members, it was quick to emphasize blood donated by Black Americans wouldn't coat the veins of white servicemen. Historians say this policy was meant to appease white Southerners who believed Black blood was inferior to their own.This policy was leaked to the press that same year.

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.)

Human origins 101

Learn about the over 20 early human species that belong in our family tree and how the natural selection of certain physical and behavioral traits defined what it means to be human.

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.

Every virus is classified into 7 groups based on genetic differences

Viruses infecting humans have been named based on symptoms ("chickenpox") or the location or animal in which they were first discovered ("Bolivian Haemorrhagic Fever" and "Monkeypox"). For clarity among scientists and to reduce stigma, virologists classify the 15,000 known viruses (270 of which infect humans) by their basic genetic material.

How we helped make Aedes aegypti mosquitoes such a problem

Mosquito genome sequencing data suggests that Aedes aegypti mosquitoes first started specializing on human blood around 5,000 years ago—when climates shifted and humans started domesticating plants in Africa and stored large amounts of water that may have attracted the bugs.

Why some people have allergies

Why do some people have allergies while others don’t? One theory suggests allergies are a relic of our evolutionary past. Our immune system, once primed to fight parasites, now mistakes harmless substances for threats.

What we know about aurochs, the ancestors of modern cattle

The relationship between humans and cattle is invaluable and longstanding. Evidence suggests cattle's wild, larger, and now-extinct ancestors, the aurochs, were also linked to early humans. Similarly valuable for their milk and labor power, yet significantly more threatening due to their size, aggression, and speed, auroch domestication was slow and complex. Discover new information about the fascinating ancestors of modern cows and the potential of re-introducing the species with selective breeding.

The anthropological origins of modern race science

The year 1961 saw the launch of The Mankind Quarterly, a new scientific journal of anthropology that hid its political propaganda behind a veneer of academia, expecting readers to assume whatever lay in its pages was scientifically proven. This in-depth article details how this journal pushed race science in the hopes of blocking racial integration in the US and preventing the immigration of those outside of Western Europe.

Ancestry testing matches DNA to known genetic variants found in specific ancestries

After a lab receives a person's sample, the DNA is separated into single strands, which are chemically cut into smaller fragments. The fragments are then fed into an array of variants of known origins, and technicians observe if a person's fragments bind to specific variants.

Genetic blood test offers an estimated clock on when Alzheimer's symptoms may appear

The 2026 research finding from researchers at Washington University School of Medicine in St. Louis—if validated in broader populations—suggests that an already available blood test could estimate when Alzheimer's symptoms may begin within a margin of several years. The test detects a protein called p-tau217 found in blood plasma and the researchers incorporated the findings from that blood test into a statistical model to come up with the symptom timeline predictions.

What is the blood brain barrier?

Every blood vessel is lined with endothelial cells that act as filters between blood and the rest of the body. In the brain, these cells are tightly packed together to keep a close watch on what substances can access the vital organ. This protective measure poses an obstacle to drugmakers looking to deliver drugs to the well-defended brain for conditions like Alzheimer's. Watch a quick overview here.

Autoimmune diseases affect between 5% and 10% of people worldwide, but their causes remain unknown

Autoantibodies—which attack the body—may be detectable in the body years before a patient develops symptoms, but some people may have detectable levels yet never go on to develop an autoimmune disease. This video discusses this and other unsolved mysteries with autoimmune disease.

How winemaking has changed throughout history

Winemaking is an ancient practice, and researchers continue to find evidence that this ritual came even earlier than previously estimated. This article outlines five key turning points in wine’s history, from the fermentation of fruit by our primate ancestors to today’s increasingly popular “New World” wine. Discover the fascinating scientific and cultural factors that led to wine’s changes in flavor and increased symbolic importance.

Bacteria helped scientists realize that DNA was the hereditary molecule, not proteins

Until the mid-1900s, most scientists believed genes were made of proteins, which were known to act as enzymes, hormones, and other chemicals that mediated an organism's traits. The Avery-MacLeod-McCarty and that benign bacteria could be made lethal, where the inherited factor that caused bacterial transformation contained DNA.

The origins of British pub names

An estimated 50,000 pubs dot the streets and countrysides of Britain, many of which have histories going back centuries. This deep dive traces the origins of some of the most common pub names to the medieval era, including favorites Red Lion, Crown, and Royal Oak. Learn why such names were originally chosen and how they have come to evolve in recent centuries in this comprehensive overview.

The enduring history of universal basic income

Distributing money to everyone is a radical idea provoking heated debates. The historical record shows pockets of civilizations exploring the notion around the world. The practice resembles what many prehistoric societies did as well. Trace the history of this income distribution approach with this fascinating overview.

How 'the Iceman' got his tattoos remains a mystery

Ötzi the Iceman, discovered in 1991, is one of the oldest human mummies ever found—and his 61 tattoos remain a mystery. This explainer looks at how researchers believe the tattoos were made, what their placement suggests about ancient medicine and culture, and why we’re still piecing together their true purpose today.

See how antidepressants were discovered

The decadeslong journey to the three major types of antidepressants began with medications designed to treat other maladies. Watch to learn more about how attempts to treat tuberculosis and blood pressure disorders led to new insights about neural chemistry and mood.

The ABCs and FAQs on GMOs from the WHO.

GMOs (or genetically modified organisms) are a subject of great debate in the food world…but how come? GMOs are organisms whose genetic materials have been altered in a way that does not occur naturally in order to create a product that has a...

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

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

At the beginning of the 20th century, a group of young men ate standard American food—replete with food additives like borax and formaldehyde—as part of government research to better understand food safety.

See the evolution of Ebola vaccine and treatment development.

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

A century of Billboard issues documenting the evolution of popular music.

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.

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

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.

Hookworm infection, though risky, may help fight certain autoimmune conditions by tamping down the immune system's inflammatory response.

The original copy of the Declaration of Independence is not a pristine document, and even features a smudged anonymous handprint in the bottom left corner.

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

As of 2025, the most cited papers in science include a review of graphene, methods to improve image recognition, streamlining electron density calculations, and optimizing protein studies.

Animal phobias are likely the most common type of phobias, followed by an extreme fear of heights.

Clever Hans was a 1900s horse that was believed to be able to solve math equations, tell time, and read and comprehend German, until a psychology student discovered how he got his answers.

The hormonal disorder PCOS was renamed PMOS in 2026, a move designed to improve care and research by shifting the focus to the hormonal causes of this condition that affects 1 in 8 women.

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.

The rivalry between Alexander Hamilton and Thomas Jefferson centered on federalism—the question of how much power the federal government should hold relative to the states.

Alzheimer's can lead to brain shrinkage, with an average of around 2% of volume reduction per year

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

A researcher recently discovered an interview from 1967 between groundbreaking journalist Joan Didion and the Grateful Dead, years before the band became an institution.

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

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

Chaos theory—informally known as the butterfly effect—is the reason why weather forecasts are presented with probabilities rather than certainties.

American short story writer Flannery O'Connor raised 40 peacocks, which became potent symbols for her fiction's elegant violence