This article looks at the different blood types of homo sapiens; how they matter and why we don't all have the same type. One in a series of articles I'll eventually post here dealing with the question "Why does it matter for humans to learn about our evolutionary history?" 

This article is not finished yet, but I'm putting it up here anyway. I will be working on it periodically. It starts with the basics, the blood types and how they relate (color coding my idea). It goes on to deal with how this came about. I will be adding more factual, historical data as I go along. 

The reason why blood type O is called the "universal donor" is because it can be accepted by a body which has any of the other blood types...and blood type AB is called the "universal acceptor" because a body with type AB blood can accept all of the other blood types. Ok, that is obvious. Why is that so though? 

It is so because of evolution. There is no reason for the current array and nature of blood types other than the fact that the different blood types have come about over time in different, separated people groups as a result of different genetic mutations which happened in each group. 


The reason why blood type O is the universal donor is related to the fact that it is the oldest. Since it is the oldest and all current groups have descended from the common ancestral group which had that blood type, all current groups can still accept that blood type (recall from above that A and B and AB can accept O) because it is still part of their gene pool.

At one time in our species' history, an A group and a B group got together resulting in the mixed type we now call AB. Since AB is the most recently evolved blood type, and since it is a mixture of A and B (the only other existing blood types beyond O) a body with this blood type can accept any of the other blood types.


In the species Homo Sapiens then, our bodies are only compatible with blood that is from a common ancestor on the same evolutionary branch of the tree of life. Is having different blood types that which separates us into different species though? 

No. The usual marker at which scientists draw the line between species is whether or not they can (or at least whether or not they do in the wild) successfully mate and produce viable offspring. The point at which they can't (or don't) is often enough to say that there is a distinction of species between the two. Like other things in an open system, this is not a hard and fast, absolutist rule, but simply a rule of thumb. There may be exceptions for certain species in certain circumstances, but this is usually the way the lines get drawn. 

Successful sexual reproduction is more important to our species than blood-type compatibility. Though a person with type A or B or AB blood should not give blood to person with type O, they most likely would be able to produce viable offspring despite their blood-type difference. So, in the case of blood types in humans, I guess it's not enough to draw a line between species. However, it sure is an obvious sign of the effects of geographically separated groups of the same species evolving crucial differences that make their bodies incompatible with each other on what seems to me to be a fairly fundamental level. 

So, why is this so interesting to me? It's interesting to me because of how it relates to the evolution of life on Earth, and specifically to the evolution of our species, Homo Sapiens. This blood-type branching in our species has all happened in the span of only the last 100,000 years or so...with one of the types (AB) coming into existence much more recently. 

Though we have evolved different blood-types, there has neither been significant enough changes in our environments, nor significant enough genetic changes in our species, nor has any group spent a significant enough amount of time apart from the others for their genetic changes to result in further speciation....yet. 

Although we see our species continue to grow by leaps and bounds in areas of thought, technology, culture, social structure and such, with the brain size and power that we now have to cope with and adapt to our changing environment, it is probably not very likely that we'll ever notice any further major anatomical evolution. 

Not that it could never happen. It is happening right now as you read this. However, since the mutations are so minute, and since we haven't seen any speciation in the past 100,000 years of our species existence, it is unlikely that we'll ever notice our species evolve until some pretty major environmental change...something on the scale of wiping out 99% of our species.... or perhaps something like leaving Earth to go populate some other planet which has drastically different environmental conditions which would result in revealing those of our species which have accumulated helpful mutations along the way without it ever being known before. 

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