Why are Jews compatible? It's in the genes
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Jews often think about their identity. Who am I? What does it mean to be Jewish? And as a Jew in the third generation from the Holocaust, I often think about the differences between people — and whether or not these differences matter in any way. One way to answer these questions comes from a surprising source — scientific research into the way our bodies fight disease.
All humans have a very similar set of genes but of course, there’s some variation between each of us. It turns out that the biggest genetic difference is not to do with things that are obviously different — say the genes that control hair, eye or skin colour. Instead, the genes that vary the most are our so-called compatibility genes.
These genes vary so much that in effect, they are a hallmark for our individuality. In a database of 18 million people, there are four with genes similar to mine. And six per cent of people in the 18 million are unique. However you view your place in the universe, some part of your individuality — your uniqueness — comes from the versions of these genes that you have inherited.
These are the genes that doctors try to match for some types of medical transplantation — bone marrow transplants for example — to give the best chance of the operation being a success. But of course, the natural role of these genes in the body can’t be to cause problems in transplantation, because that’s such an unnatural situation. It has taken more than six decades of research to work out what these genes really do.
Out of 18 million people, there are just four like me
First, these genes influence the way in which our bodies fight disease. The particular versions of these genes which you have inherited influence how you’ll fare in battle against all kinds of different infectious diseases. Differences in these genes are one reason why you may recover from a viral infection in a shorter time than somebody else infected with the exact same virus.
But relatively recent, and more controversial experiments indicate that these genes can also play a role in other aspects of human biology, such as influencing the sexual attraction between people and the likelihood of couples having particular problems in pregnancy. From what we know already, it seems that these genes play a role in who gets born and who lives, at several levels; the outcome being to keep lots of different versions of these genes in the population.
Every migration, immigration and conversion, has been written into the fabric of our collective genetic heritage — and especially into our inheritance of compatibility genes. Today, there are versions of these genes that are more frequently found in Jews than non-Jews. And the same could be said for other groups of people with shared ancestry.
So Jewish identity is at least in part written into our compatibility genes. More than this, there is clear variation across different populations of Jews — a fact which can be used to establish our ancestral history. Analysis of Jewish compatibility genes establishes, for example, a clear link between Ashkenazi and Moroccan Jews. Ethiopian Jews lack the versions of these genes common to Middle Eastern ancestry, yet remain distinct from other Ethiopians. In one study of non-Ashkenazi Jews, the Cochin Jews of India were identified as having the most distinct set of these genes.
Does this matter? Yes, because medicine will soon embrace our genetic differences. Some vaccines may, in the future, work better for people with particular versions of these genes. This will bring ethical dilemmas - but it’s nothing to be scared of.
Daniel M Davis is professor of immunology at Manchester University and author of The Compatibility Gene (Penguin Books, 2013)