Is Type O The Oldest Blood Type?

No, Type O is not the oldest blood type. The ABO blood group system, which includes types A, B, AB, and O, is roughly as old as modern humans themselves — all four types have been present in human populations for tens of thousands of years. The idea that Type O came first and other types evolved later is a popular story, but it does not match what the genetic and anthropological evidence shows.

Is Type O The Oldest Blood Type?

All ABO blood types are ancient. Genetic studies of the ABO gene suggest it has been around for millions of years — long before modern humans existed. Variations that produce A, B, and O have been found not just in humans but in other primates, including chimpanzees and gorillas.

That matters because it means the ABO system did not appear in a single human ancestor and then branch out into different types over time. The variants existed side by side in ancestral populations. Type O is not a newer version of A. It is one of the original versions.

What makes Type O look “oldest” to some people is its frequency. Type O is the most common ABO type in many populations worldwide, including among Indigenous peoples of the Americas, many European groups, and parts of Africa. High frequency is not the same as older origin. It often reflects natural selection, population history, or genetic drift.

How Did the ABO Blood Types Actually Evolve?

The ABO gene sits on chromosome 9. It carries instructions for an enzyme that adds sugar molecules to the surface of red blood cells. Small changes in that gene produce different versions, called alleles. The A and B alleles add slightly different sugars. The O allele produces a non-functional enzyme, so no sugar gets added at all.

That last point is important. Type O is not a distinct “type” in the way A and B are. It is the absence of the A and B sugar markers. The O allele is essentially a broken version of the gene. It arose from a mutation that disabled the enzyme.

Geneticists have estimated that the O allele appeared at least a few hundred thousand years ago, and possibly much earlier. The A and B alleles are older still. So if you line them up by age, O is not the front-runner.

What is genuinely interesting is that all three alleles have survived for so long. In most cases, a broken gene would fade out of a population. The O allele did not. That suggests it has been maintained by some evolutionary pressure — though what that pressure is remains debated.

Where Did the Idea That Type O Is Oldest Come From?

The “Type O is oldest” claim comes from a mix of pop science, diet culture, and early blood type research that got oversimplified.

One source is the blood type diet, popularized in the 1990s. Its central claim was that Type O is the “ancestral” type, dating back to Paleolithic hunter-gatherers, and that people with Type O should eat like cavemen. No clinical trial has confirmed that eating according to blood type produces health benefits. The theory has been criticized by nutrition researchers for lacking supporting evidence.

Another source is older anthropology writing that described Type O as more common in older populations. That framing confused frequency with ancestry. A trait can be common for many reasons — including random chance in a small founder population, or selection for a trait that happens to travel with the ABO gene.

There is also a persistent idea that blood types appeared in sequence: O first, then A, then B, then AB. There is no genetic or fossil evidence for that sequence. The alleles do not appear in a neat order.

Does Type O Offer Any Real Health Advantages?

Some associations between ABO type and disease risk are real and well documented. The strongest is the link between blood type and venous thromboembolism — blood clots in the veins. People with non-O blood types (A, B, and AB) have a higher risk of venous clotting than people with Type O. This is one of the more consistently reproduced findings in blood type research.

Type O is also linked to a somewhat lower risk of certain cardiovascular events, likely because of the clotting relationship. But “lower” is relative. Type O does not confer protection from heart disease in any absolute sense.

On the other side, some studies have found that people with Type O may have a slightly higher risk of certain bleeding-related conditions, including some gastrointestinal bleeding. The effect sizes in this area are modest and not always consistent across studies.

What is not established:

• That Type O people should eat a specific diet
• That Type O protects against severe infections across the board
• That Type O people have different exercise needs
• That knowing your ABO type should change routine medical decisions outside of transfusion, pregnancy, and a few specific clinical situations

Some research early in the COVID-19 pandemic suggested Type O might be slightly less susceptible to infection. Later studies were mixed. The effect, if real, appears small compared to factors like age, vaccination status, and underlying health conditions.

Why Are Blood Types Distributed Differently Around the World?

Blood type frequencies vary widely by region. Type O is most common in many Indigenous populations of Central and South America, where it can reach very high percentages. Type B is more common in parts of Asia. Type A is common in parts of Europe and among some Indigenous North American groups.

These patterns reflect population history — migration, isolation, and mixing. They also reflect selection. Certain blood types may have offered advantages or disadvantages against specific infectious diseases in specific environments.

One well-supported example involves malaria. The Duffy blood group, which is separate from ABO, affects susceptibility to one type of malaria parasite. The near-absence of the Duffy antigen in many sub-Saharan African populations is a textbook case of infectious disease shaping blood group genetics. Similar pressures may have acted on ABO, though the details are less clear.

The takeaway is that blood type distribution is not a timeline. It is a map shaped by many forces at once.

What Is the Actual Oldest Blood Group System?

ABO is not the only blood group system. There are more than 40 recognized systems, including Rh, Kell, Duffy, Kidd, and MNS. Each involves different genes and different red blood cell markers.

Some of these systems are older than others in evolutionary terms. The Rh system, for example, is also ancient and has been studied in primates. But asking which blood group system is “oldest” is a bit like asking which organ is oldest. They evolved at different times for different reasons.

Within the ABO system, the A and B alleles predate the O allele. If you want to be precise, A and B are older than O — though all three have been around long enough that calling any of them “new” would be misleading.

Does Knowing Your Blood Type Matter for Your Health?

Your ABO type matters in specific clinical situations. It matters for blood transfusions, organ transplants, and pregnancy (because of Rh incompatibility, which is a separate system but often checked alongside ABO). It matters for certain clotting risk assessments.

For most everyday health decisions, ABO type is not a major factor. It does not determine what you should eat, how you should exercise, or whether you will get a particular disease. The associations that exist are statistical and modest. They describe risk at the population level, not destiny at the individual level.

If you are curious about your blood type, a simple lab test can tell you. If you are considering any health decision based on your blood type, the evidence base is thin. Talk to a clinician rather than relying on blood type diet books or internet personality quizzes.