Blood types have long fascinated scientists and medical professionals. Of the many different blood types that exist, O blood is the most common around the world. But when and how did O blood first originate in humans? Understanding the evolution of blood types like O can provide useful insights into human history and biology.
The Basics of Blood Types
Human blood comes in four main types: A, B, AB, and O. These blood types are determined by the presence or absence of antigens – substances that can trigger an immune response – on the surface of red blood cells:
- Type A blood has A antigens
- Type B blood has B antigens
- Type AB blood has both A and B antigens
- Type O blood has neither A nor B antigens
People can only receive blood transfusions from a type that matches their own. For example, a person with type A blood can only receive type A or O blood. This is because unmatched antigens on transfused blood can provoke an immune reaction.
The majority of humans have one of the main four blood types. Distribution varies around the world, but O blood makes up the highest percentage globally. Around 63% of Asians, 51% of Europeans, 47% of Americans, and 43% of Africans are type O.
The Appearance of the O Gene
Blood types depend on inherited genes that control antigen production. The gene for type O blood is thought to be the ancestral or original gene shared by all humans. Around 1-2 million years ago, mutations occurred in this gene that produced the A and B antigens.
So while O type blood has no antigens, it also lacks the mutations that lead to the antigenic types A and B. This is why O blood is considered the universal donor – it contains no antigens for other blood types to react to.
So when did humans first develop the O blood type? Research indicates it arose alongside the early evolution of our species:
- Around 200,000 years ago, the first anatomically modern humans, Homo sapiens, emerged in Africa.
- Some of the earliest known remains of Homo sapiens, dated to around 100,000 years ago, show traits consistent with type O blood.
- Genetic studies suggest all humans shared a common ancestor in Africa around 200,000 years ago, inheriting the O gene.
In other words, the O blood type appears to be as old as our species itself. It was the first and only blood type among early modern humans. All human populations inherited and share this blood type from our common African ancestors.
The Spread of A and B Blood Types
For the first 100,000 years or so of human history, O positive was the dominant and only blood type on Earth. So when and how did A and B blood types emerge and spread? Here’s what we know:
- Around 80,000-100,000 years ago, a mutation in the O gene occurred that produced type A blood.
- About 20,000 years ago, another mutation produced type B blood.
- Both mutations likely first occurred somewhere in Asia or Europe before spreading worldwide.
These genetic mutations created new antigen types A and B that provided additional variety. Over many generations, the mutations spread through populations and became common in certain parts of the world.
Distribution of Blood Types Today
Here is an overview of the distribution of blood type frequencies around the world today:
| Blood Type | Region/Ethnicity | Frequency |
|---|---|---|
| O+ | Europe, Americas, Australia | 37% |
| O+ | Africa | 47% |
| O+ | Asia | 35% |
| A+ | Europe, Americas, Australia | 36% |
| A+ | Africa | 27% |
| A+ | Asia | 27% |
| B+ | Europe, Americas, Australia | 8% |
| B+ | Africa | 18% |
| B+ | Asia | 26% |
| AB+ | Europe, Americas, Australia | 4% |
| AB+ | Africa | 4% |
| AB+ | Asia | 9% |
While O continues to be the most common worldwide, the frequencies of A and B blood types can vary dramatically between regions and ethnicities. For example, B blood type is found in 26% of Asians but just 8% of Europeans.
Advantages of Different Blood Types
Although all humans originally had O blood, the development of A and B blood types offered some potential benefits:
- Greater diversity in blood types allows for more successful blood transfusions between people with matching types.
- Some blood types appear to provide resistance to certain diseases like malaria. For example, the A allele is associated with higher malaria resistance.
- Rare blood types can provide a degree of protection from pathogens adapted to more common blood types in a population.
The emergence of new blood types thus increased overall genetic and antigen diversity within the human species. This provided humans with a survival advantage by enhancing defenses against infection and disease.
The Appearance of Rhesus Blood Types
In addition to ABO antigens, human blood also contains another important antigen class known as Rhesus or Rh factor:
- If your blood has the Rh antigen, you are Rh positive.
- If your blood lacks Rh, you are Rh negative.
- Around 85% of humans are Rh positive. The remaining 15% are Rh negative.
The roots of Rh factor trace back around 30,000-50,000 years to populations in Europe and Asia. An ancient mutation removed the Rh antigen from some individuals. This mutation persisted and spread due to benefits like increased fertility. But its origin likely occurred tens of thousands of years after the emergence of ABO blood types.
Conclusion
In summary, the O blood type traces its ancestry back hundreds of thousands of years to the origin of our species. It was the universal blood type of early humans. Around 80,000-100,000 years ago, mutations produced new A and B antigens, creating additional blood type diversity. Rhesus blood types emerged much later, about 30,000-50,000 years ago.
Understanding the long history of O blood and other blood types provides insights into humanity’s deep evolutionary past. Blood types illustrate how dynamic evolutionary forces have continued shaping human biology and diversity long after the emergence of modern humans.