Blood

by Read Listen Learn

“Everybody is a book of blood; when we are opened, we’re red.” - Clive Barker

Our blood is literally vital. It carries nutrients and oxygen around the body and takes away waste. Blood is seen as sacred in many religions; it is the ‘seat of the soul’ which is why it must be drained from any meat in the Islamic and Jewish faiths. And, of course, blood is a little different from animal to animal and may be adapted to their special needs. The camel, for example, has special blood cells that allow it to survive sudden, dramatic changes of temperature typical in the desert at dawn and dusk. Some animals also have a kind of natural anti-freeze in their blood to resist sub-zero temperatures.

And even within one species there may be several different types of blood. Cows have as many as eight hundred. Fortunately, the situation is a little less complicated for us: there are four basic types, A, B, AB and O. However, it’s not as simple as all that because each of these can be what’s called ‘rhesus positive’ (Rh+), or ‘rhesus negative’ (Rh-) which now gives us a total of eight. But what does all this mean for human beings in practical terms?

Well, not a lot really, given that we survived for about half a million years as a species without the least idea about these blood types and are able to reproduce with each other. We are, after all, the same species.

However, it does matter in the context of modern medicine. First, in the area of blood transfusions; these have been a great life-saver for about a hundred years, allowing mothers in childbirth, badly wounded soldiers or injured motorists to survive what would otherwise be fatal moments. The problem is that you can’t give any person’s blood to just anyone else. Some types, like O-, do work for everyone (or, should we say: ‘every body’?), and these types are called ‘universal donors’. But some types of blood will be rejected by people with other types needing a transfusion.

In some cases, a mother’s blood will be incompatible with her unborn child’s, who will be of the father’s blood type. Essentially, the mother’s body will see the baby inside her as a ‘foreign body’ and her immune system will go on the attack, which leads to a natural abortion. Luckily, these days, doctors can give women in this situation special medicines to stop their immune systems from doing this.

Until the full development of DNA in the last fifteen to twenty years, blood type was the only way to settle paternity cases. It was not as accurate as DNA but did give a very good idea in many cases and virtual certainty (99.99%) in some.

Some tribes have developed special blood to resist blood parasites like malaria and dengue. Many people coming from West Africa and the Eastern Mediterranean and their descendants have something called ‘sickle cell trait’ which doesn’t stop them catching malaria but reduces the symptoms of the disease, otherwise often fatal, to a head cold.

Sickle cell trait is no mystery. We know how and why it developed, but the big mystery of human blood is the rhesus negative category. Scientists categorised our blood into its types based on the blood of our evolutionary cousins, the rhesus monkey, but then discovered that, in some cases, there was no trace of ‘rhesus’ in the blood. One theory to explain this is that ‘not rhesus’ or Rh- humans may not be descended from the rhesus monkey. This is 15% of the human population.

The worrying part is that human Rh- blood doesn’t resemble the blood of any other mammal, let alone monkeys. In fact, it closely resembles the structure and style of lizard blood. People who are Rh- are not found in equal numbers all over the earth. They are only one per cent of the population of China, for example, but up to twenty per cent of the Irish and Basque populations.

Theories about the origin of Rh- blood are not in short supply. There is no time to consider them all here but let’s look at two extremes. Some scientists have suggested that it is the result of a genetic mutation of the sort that created red-haired people. At the other end of the line of argument, some people say that this blood type comes from a race of lizard-like aliens who visited our planet many thousands of years ago and, against all the odds, managed to have children with some of our human females.

Of course, this last idea seems, well, a little improbable, to put it politely, but, just the same, the origin of Rh- blood is a mystery that modern science is still powerless to solve.

Finally, and on a romantic note, the Japanese see blood types as a good indicator of personality type. People with AB are sociable but bad at making decisions; those with O are leaders and very ambitious and so on. So, in Japan, when you chat someone up, you don’t ask for their zodiac sign, you ask their blood type to see if you will be compatible.