The human body is a miraculous thing. Millennia of evolution: random mutations, trial, and error have resulted in what we are today.
Evolution isn’t a straightforward process, however. There are still a lot of things about the human body we don’t understand. We have features and quirks that don’t always seem to have an obvious purpose or make sense.
Take for example blood types. Why did humans evolve to have separate blood types? Are they of any use? Or are they just an evolutionary throwback?
What is a Blood Type?
Most of us are familiar with the four main blood types, A, B, O, and AB. These blood types were discovered in the early 1900s by the Austrian physician Karl Landsteiner.
Landsteiner discovered that some people’s blood cells were coated with antigens (something that causes a response from the body’s antibodies, such as viruses and bacteria) while some people didn’t have any at all. He found there were two types of these antigens. He used these to split people into four groups.
Type A people have A antigens. Type B people have B antigens. Type AB people have both types. Those who had no antigens at all? Type O.
He found that the blood of types A and B people wasn’t compatible with one another as their bodies produced antibodies that attacked the other blood type. People with type O blood produce no antigens, meaning it provokes no immune response. This makes them universal donors.
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Complicating things further, in the last 100 years scientists have discovered there aren’t just four blood groups. There are actually over 20 known blood groups. The Rh factor denotes whether someone’s blood type is positive or negative. The Rh factors add another wrinkle to whether someone’s blood will be attacked by antibodies when used in a transfusion or not.
Why Do We Have Them?
We know that the blood groups are ancient and that they are a trait we share with other members of the ape family. It is believed the blood types were inherited from a common ancestor at least 20 million years ago or even further back.
It is believed type A blood is the oldest as it has been found in the fossils of very early hominids (pre-humans). It is believed type 0 came next, followed by the others although we have no exact dates.
So what caused the emergence of new blood types? Well, our blood type is inherited from our parents and is governed by a single gene. This gene comes in three flavors, A, B, and O.
So at some point, the A gene mutated and the B and O genes were created. Random mutations in human DNA happen all the time. When we reproduce these mutations are passed down to our offspring. Pretty much every trait that divides us as a species is the result of a random mutation. As is everything that makes us different from our hairier cousins.
It’s important to remember that evolution isn’t planned or sentient. As humans evolved we weren’t following some grand blueprint. There were lots of random mutations.
Those which proved to be beneficial helped those who carried them survive and pass on the mutated gene. The negative mutations? Less likely to be passed on as the holders were less likely to get a chance to reproduce.
The confusing thing about blood types is, at least initially, scientists couldn’t see how they benefited our ancestors. They appeared to be a largely useless trait that somehow became prevalent.
Are There Any Advantages?
As we said above, evolution isn’t planned. More often than not it takes a scattershot approach. This means we often end up with lots of variations of the same thing, some more or less efficient than others.
It is important to understand this is a good thing. If we were all genetically identical and our bodies all worked the same, we wouldn’t last long as species. If something could kill one of us, it could kill all of us.
Scientists have discovered that people with different blood types are resistant to different types of diseases. For example type A people seem to be more susceptible to smallpox. On the other hand type B people struggle to fight off certain types of E. coli.
The most significant example of this is Malaria, a disease that continues to kill hundreds of thousands of people every year and ruin the lives of countless more.
The Duffy blood group has antigens that attract one of the parasites that cause malaria, Plasmodoim vivax. These parasites love nothing more than to latch on to Duffy antigens, causing malaria.
People who don’t have the Duffy antigens tend to be largely immune to this deadly disease. 85% of West Africans are Duffy A and B negative, evidence that people who lack the Duffy antigens tended to survive while those carrying them were killed off by malaria.
As time goes on scientists are discovering more and more diseases that different types of blood groups are resilient/weak to. Without this natural variation in blood types, diseases like malaria and smallpox would have wiped us out long ago.
An Advantage in Diversity
The existence of blood groups often gets a bad rap. Blood groups complicate giving blood transfusions. Giving someone the wrong blood type can have deadly consequences. Without blood types giving and receiving blood would be as simple as giving your car an oil change.
But science has shown us that blood types are just another example of the wonders of evolution. Rather than being a nuisance, it seems that blood types are yet another random mutation that has allowed humans to thrive. They shield our population and help make sure one deadly disease can’t wipe us all out in one go.
Top Image: We have identified 20 different types of blood across our species: why does our blood differ so much? Source: Phonlamaiphoto / Adobe Stock.
By Robbie Mitchell
References
Wayman. E. 2012. The Mystery of Human Blood Types. Smithsonian Magazine. Available at: https://www.smithsonianmag.com/science-nature/the-mystery-of-human-blood-types-86993838/
Spiegel. F. 2013. Blood Purity: How a Bizarre Obsession Advanced Science. ABC News. Available at: https://abcnews.go.com/International/blood-purity-bizarre-obsession-advanced-science/story?id=19296143
Mayer. M. 2022. Dr. Universe: Why are there different blood types? Dr. Universe. Available at: https://askdruniverse.wsu.edu/2017/08/28/different-blood-types/
Farhud. D. Yeganeh. Y. 2013. A Brief History of Blood Types. National Library of medicine. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3595629/
